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Isopod parasites of Pygocentrus piraya (Characiformes: Serrasalmidae) in the lower São Francisco River, Brazil
research-article
Author(s):
André Mota Alves ,
Marcos Vinícius Teles Gomes ,
Uedson Pereira Jacobina ,
Marcelo Fulgêncio Guedes Brito
Publication date (Print and electronic):
2024
Journal:
Nauplius
Publisher:
Sociedade Brasileira de Carcinologia
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Abstract
Abstract Isopods of the suborder Cymothoida include ectoparasite species that cause physical damage and affect the development of the host by feeding on blood and tissues. On fishes, these parasites attach themselves to the skin, fins, gills, and oral cavity using claws on articulated legs. The ability to remain hidden in cavities even after the fish is caught enables isopods to be transported to new areas along with the host, making these parasites potential co-invaders. Understanding the role and environmental impact of parasites is essential, although research on parasitism in the context of biological invasions lags in comparison to general research on such invasions. Previous records indicate only two species of parasitic isopods in the São Francisco River basin. However, the present study reports the first record of two other species (Braga patagonica and Braga nasuta) on Pygocentrus piraya and in the basin itself. This demonstrates a lack of knowledge regarding fish parasites in the region, despite the presence of other parasites. Collaborations with research groups conducting fish sampling in the basin can contribute to expanding knowledge on these parasites and the training of human resources in fish parasitology. The present study provides important information on the presence of unidentified parasitic isopods on fishes in the São Francisco River basin, underscoring the need for further studies and expanding the geographic distribution of these parasites, as well as the host list for these isopods.
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Most cited references48
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The Fishes of the Amazon: Distribution and Biogeographical Patterns, with a Comprehensive List of Species
Fernando C.P. Dagosta, Mário Pinna (2019)
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Co-invaders: The effects of alien parasites on native hosts
1 Introduction Invasive species are alien (non-native) organisms that have been introduced into an area outside of their natural range, established self-sustaining populations and spread beyond their initial point of introduction, with deleterious impacts on the environment, the economy or human health (Kolar and Lodge, 2001). Human population growth, increasing transport capacity and economic globalisation have accelerated the rate of introductions of alien species throughout the world (Vitousek et al., 1997; Sakai et al., 2001). Invasive species are now recognised as a major cause of biodiversity loss and associated changes in ecosystem function, leading to biotic homogenisation as native species are replaced by widespread alien species (Pimentel, 2002; Rahel, 2002; Simberloff, 2011). There has been a dramatic growth in the study of biological invasions in the last twenty years, with a concomitant and confusing amplification of terminology (Falk-Petersen et al., 2006; Blackburn et al., 2011). Blackburn et al. (2011) proposed a unified framework for biological invasions that describes the status attained by alien species as they progress through a series of barriers in their new environment. In this framework, an alien species must surmount geographic barriers to be introduced into a new area, then barriers to survival and reproduction to become established within the expanded range, and finally barriers to dispersal to become invasive (Table 1; Fig. 1a). No specific terms have been proposed to distinguish alien species which adversely affect the environment, economy or human health from those which do not have adverse effects, but in practice the term “invasive” usually connotes negative impacts, particularly on the environment (Falk-Petersen et al., 2006). Invasive species may affect native species directly, through competition or predation, or indirectly, by altering habitat or changing disease dynamics. Parasites may play a key role in mediating the impacts of biological invasions at any of the three phases of introduction, establishment or spread. Introduced alien hosts often have fewer parasite species and a lower prevalence of parasites than native hosts, which may provide them with a competitive advantage (enemy release; Mitchell and Power, 2003; Torchin et al., 2003). Once introduction has occurred, parasite transmission may occur from native hosts to alien hosts, leading to an increase in infection of natives if aliens amplify transmission (spillback; Kelly et al., 2009; Mastisky and Veres, 2010) or a decrease in infection of natives if aliens reduce transmission (dilution; Paterson et al., 2011; Poulin et al., 2011). If alien hosts introduce new parasites, then these may be transmitted to native hosts, leading to the emergence of new disease in the natives (spillover or pathogen pollution; Daszak et al., 2000; Taraschewski, 2006). To threaten native hosts in a new locality, alien parasites must overcome the same barriers to introduction, establishment and spread as free-living aliens and, in addition, they must be able to switch from alien to native hosts. We propose using the terminology of co-introduced for those parasites which have entered a new area outside of their native range with an alien host, and co-invader for those parasites which have been co-introduced and then switched to native hosts (Table 1; Fig. 1b). It does not seem useful to make a distinction between introduced and established alien parasites, in the same way that this distinction is made for free-living aliens, because, except in very special circumstances (e.g., MacLeod et al., 2010), introduced parasites which do not establish are unlikely to ever be recorded. Similarly, we see little value in distinguishing between alien parasites in established alien hosts and those in invasive alien hosts if they have not switched to native hosts, as this is the crucial step in parasites adversely impacting the new environment. Although co-invading parasites are often considered to be important causes of disease emergence, producing high morbidity and mortality in native hosts (Taraschewski, 2006; Peeler et al., 2011), the extent to which co-introduction and co-invasion occur and the magnitude of the threat posed to native species have not been well documented (Smith and Carpenter, 2006). In this paper we will review previous studies on co-introduced parasites, examine the characteristics associated with host switching and compare the relative pathogenicity of co-invaders to native and alien hosts. 2 Recognising alien parasites It is not always straightforward to determine whether a newly discovered parasite is alien or native to a region. Cryptogenic species, those that are not demonstrably alien or native, appear to be remarkably common in terrestrial, freshwater and marine ecosystems (Carlton, 1996). This is partly because human-mediated transport of organisms began long before taxonomic surveys and species monitoring programs, and partly because many species, particularly of parasites, are difficult to identify or have ambiguous taxonomies (Thomsen et al., 2010). For cryptogenic species, there are a number of historical, biogeographic, genetic, taxonomic and ecological criteria that can be used to determine alien or native status. Chapman et al. (2012), for example, inferred that the parasitic isopod Orthione griffenis, which infects mud shrimps, had been introduced to North American coastal waters based on its conspecificity with disjunct Asian populations, earliest collections in Asia, late discovery in North America, and appearance coincident with extensive ballast water traffic from Asia. Gaither et al. (2013) inferred the introduced status of the nematode Spirocamallanus istiblenni in native and cultured alien fishes in Hawaii through its phylogenetic similarity to a disjunct lineage in French Polynesia, low genetic diversity, indicating a founder effect, and a lag between alien host and parasite geographic distribution in Hawaii. 3 Introduction and establishment of alien parasites Parasites may occasionally be introduced into a new locality without their host(s). For example, it is likely that free swimming stages of the isopod O. griffen is were transported in ballast water to North America (Chapman et al., 2012). Similarly, eggs and juveniles of the swimbladder nematode Anguillicola crassus, a parasite of the Japanese eel Anguilla japonica, were introduced by aquaculture transport vehicles into the United Kingdom, where they have successfully parasitised native European eels, Anguilla anguilla (Kirk, 2003). Alien parasites may also be introduced with native hosts, if those hosts have been translocated, acquired infection with a new parasite species and then been re-introduced into their original habitat. For example, the natural host of the parasitic brood mite Varroa destructor is the Asian bee Apis cerana. The European honeybee Apis mellifera acquired the mite when it was introduced to Asia early in the 20th century. Although the details are unclear, it appears likely that the mite was then introduced into Europe with infested European honeybees, rather than with the alien Asian bee (Oldroyd, 1999; Anderson and Trueman, 2000). Most alien parasites, however, are co-introduced with an alien host species. A literature survey identified 98 examples of co-introductions of alien hosts and parasites, across a wide range of taxa (Fig. 2; Supplementary data, Table S1). The most common co-introduced parasites found in published studies were helminths, making up almost 49% of the total, with arthropods at 17% and protozoans at 14% (Fig. 2a). This is likely to reflect, at least in part, our selection criteria for studies that had good evidence for parasite co-introduction with an alien host. Although viral and bacterial microparasites are generally considered to be much more important than macroparasites as emerging pathogens in wildlife, in many cases their origin is unclear (Daszak et al., 2000; Dobson and Foufopoulos, 2001) and they made up only 9% of parasite co-introductions that we found. Fishes were by far the most common alien hosts in published studies, making up 55% of the total (Fig. 2b), with 81% of fish hosts being either freshwater or diadromous. This may reflect a taxonomic bias in studies, but is also likely due to the propensity for freshwater ecosystems to be particularly affected by invasive fishes (García-Berthou, 2007; Johnson and Paull, 2011). It is now well established that introduced alien species usually harbour significantly fewer parasites than native species (Mitchell and Power, 2003; Torchin et al., 2003; Lymbery et al., 2010; Roche et al., 2010). This may arise because founding populations of aliens do not carry the complete range of parasites found in the source location or because co-introduced parasites are unable to complete their life cycle (i.e., to establish) in the new environment. Ewen et al. (2012) found that avian malaria parasites (Plasmodium spp.) that have successfully invaded New Zealand are more prevalent in their native range than related species of Plasmodium that have not invaded, and Torchin et al. (2003) reported similar findings across a range of host and parasite taxa. This may argue in favour of the importance of arrival with the host, as a higher prevalence means a greater probability of being present in host founders (Ewen et al., 2012), but a higher prevalence may also indicate a greater transmission efficiency and therefore a greater ability to persist in the new environment. Distinguishing between these two processes is not usually possible because data on host and parasite founding populations are lacking. MacLeod et al. (2010) used a host/parasite system for which such data were available – chewing lice on introduced birds in New Zealand – and found that failure to persist in the new environment was a much more important source of loss of parasite species than was failure to arrive with their hosts. It is usually considered that the establishment of parasites in a new environment is much more likely to occur in those species with simple, direct life cycles (vertical transmission or horizontal transmission without the need for intermediate hosts; Dobson and May, 1986; Bauer, 1991; Torchin and Mitchell, 2004). Dobson and May (1986), for example, suggest an order of magnitude difference in the establishment of directly transmitted parasites compared to those with an indirect life cycle. There have been no empirical tests, however, of this hypothesis, because of the difficulty in obtaining data on parasite founding populations, prior to establishment. Mitchell and Power (2003) found that invasive plant species had proportionally more viral than fungal co-introductions (24% fewer viruses and 84% fewer fungi than in their natural range) and suggested that this reflects, in part, a greater tendency for viruses to be seed-transmitted. In the 98 examples of parasite co-introductions in Table S1, 64% of parasites had a direct life cycle and 36% had an indirect life cycle (Fig. 2c). This suggests that parasites with a direct life cycle might establish more readily in a new environment, but it is not a proper test of the hypothesis because we have no data on parasite co-introductions which failed to establish. The data are also affected by a taxonomic bias. Twenty-two of the parasites (22.4%) were monogeneans, all of which have a direct life cycle. If these are excluded, then the ratio for published examples of co-introductions becomes 54% with a direct life cycle and 46% with an indirect life cycle. For co-introduced parasites with an indirect life cycle, successful establishment requires an alternative host which is already present in the recipient locality. For example, native copepods can act as intermediate hosts for the introduced nematode S. istiblenni, infecting fishes in Hawaii (Gaither et al., 2013), and native dragonflies and damselflies are intermediate hosts for the introduced trematode Haematoloechus longiplexus in American bullfrogs (Lithobates catesbeianus) on Vancouver Island, Canada (Novak and Goater, 2013). The surprising aspect from published studies is the frequency with which co-introduced parasites with indirect life cycles can establish in the new environment, with examples of successful co-introductions in protozoan, myxozoan, trematode, cestode, nematode, acanthocephalan and pentastomid parasites. 4 Host switching by alien parasites Parasites which are co-introduced with their hosts may establish and spread geographically in their new range with their original, alien host, without switching to native hosts. Although 78% of the 98 examples of co-introduced parasites in Table S1 were recorded in native hosts (i.e., became co-invaders), this is likely to overestimate the real incidence of host-switching, as null studies are generally less likely to be reported (Arnqvist and Wooster, 1995). Co-introduction without host-switching has been found, for example, in monogenean parasites of invasive pumpkinseed fish (Lepomis gibbosus) in the Danube River Basin, Central Europe (Ondrackova et al., 2011), the lungworm Rhabdias pseudosphaerocephala in cane toads (Rhinella marina) in Australia (Pizzatto et al., 2012), and the trematode H. longiplexus in American bullfrogs in Canada (Novak and Goater, 2013). We found no evidence from published studies of an effect of life cycle on host switching. Of the 98 parasite co-introductions in Table S1, 76.2% of parasites with a direct life cycle, and 80.0% of parasites with an indirect life cycle successfully switched to native hosts (Fig. 2c). This does not represent a particularly strong test of the influence of life cycle on propensity to switch hosts, because it does not control for parasite or host phylogeny or for many of the other factors which may influence the propensity for host-switching to occur. These factors include host specificity and the similarity of host fauna and environmental conditions between source and recipient localities (Bauer, 1991; Kennedy, 1993). Nevertheless, it appears that not only are many parasites with complex, indirect life cycles able to be co-introduced and establish readily in a new environment, they are also no less likely to infect native hosts and become co-invasive than are parasites with direct life cycles. 5 Virulence of co-invaders to native hosts Of the 76 examples of co-introduced parasites that switched to native hosts, we were able to obtain information on relative virulence in 16 of them, from estimates of pathogenic effects in either naturally or experimentally infected hosts. Of these 16 parasites, 14 (85%) were more virulent in native hosts than in the co-introduced alien host, while for the other two, there was no evidence of any difference in virulence between native and alien hosts. The effect of the swim-bladder nematode A. crassus on the Japanese eel (A. japonica) and the European eel (A. anguilla), provides a clear example of increased virulence in native, compared to alien hosts. A. crassus is a common parasite of Japanese eels in east Asia, but is generally found at low intensities, with no obvious adverse effects on the swim-bladder or the general condition of infected eels (Nagasawa et al., 1994). The parasite was introduced to Europe with imported Japanese eels in the 1980’s and successfully colonised European eels (Kirk, 2003). Worm intensities are typically greater in naturally infected European eels than in Japanese eels, and infection is associated with enlargement of the swim-bladder, thickening and fibrosis of the swim-bladder wall, haemorrhage, secondary bacterial infections and acute and chronic inflammatory responses (Kirk, 2003). Infected European eels have reduced appetite and poor body condition (Nagasawa et al., 1994). Knopf and Mahnke (2004) experimentally infected eels with A. crassus larvae and found that, compared to Japanese eels, worms in European eels had significantly greater survival rate and faster development, leading to a greater adult worm burden. It has been proposed that parasites which switch from introduced host species to native host species will have greater pathogenic effects in native hosts, with which they have no coevolutionary history (naïve host syndrome, Mastitsky et al., 2010; novel weapon hypothesis, Fassbinder-Orth et al., 2013). The coevolution of parasites and their hosts is often viewed as a contest between parasite virulence (parasite-induced reduction in host fitness; Combes, 2001) and host resistance (ability to prevent infection) or tolerance (ability to limit the damaging effects of infection) (Best et al., 2008; Svensson and Råberg, 2010). The naïve host theory is that parasites and hosts with a long coevolutionary history will be co-adapted; when alien parasites are introduced to a new area they meet naïve hosts which lack coevolved resistance or tolerance, and therefore are more likely to become infected and/or to suffer greater pathogenic consequences from infection (Allison, 1982; Mastitsky et al., 2010; Fassbinder-Orth et al., 2013). Although the naïve host theory appears to be implicit in many discussions of the impacts of co-invading parasites on native hosts (e.g., Daszak et al., 2000; Prenter et al., 2004; Peeler and Feist, 2011; Peeler et al., 2011; Britton et al., 2011a), there are at least two reasons why it should be viewed sceptically. First, we often cannot assume a coevolutionary relationship between a parasite and the alien host with which it is introduced, particularly for widespread alien hosts which may have acquired the parasite relatively recently (Taraschewski, 2006). Second, and more importantly, there is no a priori reason to expect the consequences of infection to be more severe in immunologically naïve host species, than in host species with which the parasite has coevolved. Because parasites generally have larger population sizes and shorter generation times than their hosts, they are expected to be ahead in the coevolutionary arms race and therefore to have greater mean fitness in local than in foreign host populations (Kaltz and Shykoff, 1998; Dunn, 2009). Parasite fitness, however, may be enhanced either by increased or decreased virulence, depending on the circumstances of transmission (May and Anderson, 1983; Ebert and Herre, 1996). Indeed, if the new host is not phylogenetically closely related to the coevolved host, then any level of virulence might result, because virulence expressed in an unusual host will not necessarily relate to parasite fitness (Ebert, 1995). Nevertheless, co-invading parasites may exhibit greater virulence to new, native hosts than to the alien hosts with which they were introduced, simply by chance. The probability of introduced hosts surviving the translocation process is likely to be inversely related to the virulence of any parasites they carry into their new range, because most introductions involve a few individuals being transported over difficult geographic barriers or escaping from captivity (Blackburn et al., 2011). As a consequence, parasites with lower virulence in their natural host will be much more likely to be co-introduced (Strauss et al., 2012). If virulence of the parasite differs between the coevolved alien host and the new, native host, it is therefore more likely to be in the direction of increased virulence in the new host. The introduction and spread of a new, virulent parasite may have catastrophic effects on native host populations. Both theoretical and empirical studies have demonstrated that parasites can provide density dependent regulation of their host populations through effects on host mortality and fecundity rates (Anderson and May, 1992; McCallum and Dobson, 1995; Hudson et al., 1998). If the parasite is relatively avirulent in the co-invading alien host, then this host can act as a reservoir of infection for native hosts, even as their populations decline (McCallum and Dobson, 1995; Daszak et al., 2000; Holt et al., 2003). There are, unfortunately, many apparent examples of this phenomenon. On the International Union for Conservation of Nature list of the world’s worst invasive species, infectious disease is the main driver behind the impact of invasion in almost 25% of cases (Hatcher et al., 2012). In many instances, these diseases are caused by co-introduced parasites that have switched from alien to native hosts. Plasmodium relicta (causing avian malaria), for example, was introduced to Hawaii with alien birds (and the primary mosquito vector, Culex quinquefasciatus) in the early 20th century. Native bird species are much more susceptible than alien species, suffering mortality rates of 65–90%, contributing to the extinction of almost half of the endemic bird fauna of Hawaii (Warner, 1968; Woodworth et al., 2005). Squirrel parapoxvirus (Chordopoxviridae; uncertain taxonomic status) is likely to have been introduced into the UK with grey squirrels (Sciurus carolinensis) from North America. The virus has no clinical effects on grey squirrels, but can also infect red squirrels (Sciurus vulgaris), causing high mortality rates and a decline in red squirrel populations (Tompkins et al., 2003; Rushton et al., 2006). Crayfish plague, caused by the fungus Aphanomyces astaci, has caused dramatic population declines in freshwater crayfish species throughout the world (Holdich and Reeve, 1991; Söderhäll and Cerenius, 1999; Evans and Edgerton, 2002). The parasite is largely asymptomatic in its natural North American freshwater crayfish hosts, but when spread with these hosts (or with ballast water or fish vectors) to new localities, has proved to be virulent in many European, Asian and Australian crayfish species (Holdich and Reeve, 1991; Söderhäll and Cerenius, 1999; Evans and Edgerton, 2002). 6 Control of invaders and co-invaders Invasive species are recognised as a major threat to biodiversity and much effort is extended in their control (Hauser and McCarthy, 2009; Sharp et al., 2011; Britton et al., 2011b). The intended outcome of such control programs is the recovery of native species or ecosystems, although control of invasive species may have unintended consequences that prevent this outcome being realised (e.g., Bergstrom et al., 2009; Walsh et al., 2012). The effect of control programs on co-invading parasites has rarely been considered, but should be included in risk assessments prior to management interventions to control invasive species, because both invasive hosts and their co-invading parasites may fundamentally alter ecosystem function (Roy and Lawson Handley, 2012; Amundsen et al., 2013). In standard models of microparasite population dynamics, transmission rate is inversely related to virulence (Anderson and May, 1992), so we should expect that if introduced parasites are usually more virulent in native hosts, then alien hosts will act as reservoirs of infection, amplifying the effects of the parasite in native hosts. This seems to have occurred, for example, with avian malaria in Hawaii, the squirrel poxvirus in the UK and crayfish plague throughout Europe, where the natural, alien hosts increased transmission to native hosts (Dunn, 2009; Hatcher et al., 2012). If invasive aliens are more competent to transmit infections than native species for a co-invading parasite, then control of the alien will reduce the infection pressure on native hosts. The situation may not be so straightforward for many macroparasites, however. The expected inverse relationship between virulence and transmission rate arises from a simple mass action model of transmission, where transmission rate depends on the numbers (or densities) of infected and susceptible hosts, and increasing virulence removes infected hosts from the population (McCallum et al., 2001). In reality, the transmission process is likely to be much more complicated, particularly for parasites with complex life cycles, and there is limited theoretical or empirical support for a general trade-off between virulence and transmission rate (Ebert and Bull, 2003). Alien hosts, therefore, may not always act as amplifying reservoirs, even when the parasite is less virulent in them than in native hosts. If invasive aliens are less competent to transmit infections than native hosts, then control of the alien may inadvertently amplify infection of natives. Whether this is likely to constitute a real problem for the control of alien species is not known, because there are very few empirical data on the relative competencies of different hosts for the transmission of any multi-host parasites (Haydon et al., 2002), let alone for alien and native hosts in transmitting co-invading parasites. 7 Conclusions It appears from published studies that co-introductions of parasites with alien hosts occur over a wide range of parasite and host taxa and often involve parasites with complex life cycles that require an alternative host in the new locality. Parasites of freshwater fishes are particularly well represented in the literature and this may reflect the susceptibility of freshwater environments to alien introductions. Once established, infection of native hosts is common and, from the limited data available, virulence is usually greater in native hosts than in the alien host with which the parasite was introduced. Successful control of the alien host may reduce the impact of the parasite on the native host population, if lower virulence in the alien host is associated with greater transmission efficiency, but we have little information on this point.
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Global diversity of fish parasitic isopod crustaceans of the family Cymothoidae
Nico Smit, Niel L. Bruce, Kerry A. Hadfield (2014)
1 Introduction Cymothoid isopods are obligate fish parasites, occurring in all oceans with the exception of polar waters. The family is primarily marine, with limited occurrence in African and Asian freshwaters, but a moderate diversity in tropical South American river systems, notably the Amazon and its tributaries. Most cymothoids occur on hosts within the 200 m bathymetric, with fewer than 10 species extending beyond 500 m in depth. The family is among the larger of the isopod families comprising some 40 genera and more than 380 species (Ahyong et al., 2011). Greatest diversity occurs within the tropics, with a rapid attenuation in diversity towards high latitudes. The Cymothoidae belongs within the suborder Cymothoida Wägele, 1989, and the superfamily Cymothooidea Wägele, 1989. This superfamily forms a clade of families that show a gradient from commensal and micropredation in the families Corallanidae, Aegidae and Tridentellidae to obligate parasitism in the Cymothoidae (Brandt and Poore, 2003). Cymothoids are large isopods, with few species below 10 mm in length or more than 50 mm in length. Characteristic of the family is that the females are far larger than the males, this trait being most strongly expressed in the buccal and gill attaching genera. Cymothoids are one of the best-known groups of isopod among the general public. They are familiar to fishers and anglers as sea lice (incorrectly – not to be confused with arguloid or caligoid copepods), tongue-biters and fish doctors, and are of interest to fish biologists and to the aquaculture industry as potential pests or disease vectors. The account of the tongue-replacing isopod (Brusca and Gilligan, 1983) achieved widespread and sustained publicity. 2 History of discovery The family Cymothoidae is unique in being among the first isopods described and being the first isopod family subjected to a comprehensive world revision (Schioedte and Meinert, 1881, 1883, 1884). Cymothoids, being relatively large (10–50 mm), came to the attention of taxonomists early in the history of crustacean taxonomy, in large part through the work of the early fish taxonomists, notably Pieter Bleeker, who would have seen and collected this ‘by-catch’. Fish collections today are still a source for undescribed cymothoids. The Cymothoidae differ significantly from all other free-living isopod families in the large number of genera and species described before 1900 and before 1950. As Poore and Bruce (2012) showed, there was a spike in the documentation of isopod species in the period 1970–1990. The Cirolanidae are typical of free-living families with 12% and 28% of species described by 1900 and 1950, respectively. In contrast approximately 42% of Cymothoidae (depending on accepted synonymies) were described by 1900, 55% by 1950 (Fig. 1). William Elford Leach (1813–1814, 1815, 1818) was the first significant contributor naming nine cymothoid species and establishing the family name Cymothoidae Leach, 1818. Earlier described species such as Cymothoa ichtiola (Brünnich, 1764), the first post-Linnaeus species to be described and Ceratothoa imbricata (Fabricius, 1775) predate the family and its genera. Leach achieved particular fame through naming eight genera based on the name Caroline and Carolina (after Queen Caroline of Britain, 1768–1821; see Bruce, 1995). Milne Edwards’ (1840) Histoire naturelle des crustacés comprenent l’anatomie, la physiologie et la classification de ces animaux can be taken as the practical start to the discovery for the Isopoda including the Cymothoidae as that publication was the first world-wide review of the Crustacea, at which point 30 species names of Cymothoidae had been proposed. Others from that era made individual contributions such as Risso (1816), Say (1818), Otto (1828) and Perty (1833). The period following Milne Edwards' (1840) work saw several taxa described, but the most significant contribution was a single work by the fish taxonomist Pieter Bleeker (1857) describing 14 species; both Edward John Miers (1877, 1880) and G. Haller (1880) each described five species. The great work of the Danish co-authors Jœrgen Christian Schioedte and Frederik Vilhelm August Meinert fixed the concept of the family that stands today, and provided a largely unambiguous concept for the Cymothoidae. This work is an outstanding contribution by the standards of the day and nothing since has come close to that breadth of coverage. Schioedte and Meinert undertook a comprehensive world revision of what is now the superfamily Cymothooidea, including the families Corallanidae, Aegidae (Schioedte and Meinert 1879a,b) and Cymothoidae (Schioedte and Meinert 1881, 1883, 1884) in an age that had no ‘rapid communication’, no rapid shipping and no rapid international travel. Schioedte and Meinert borrowed specimens from the major museums of the western world of Europe and the USA. Again, ahead of their time, they specified both the provenance and the holding institutions of the specimens that they examined. Schioedte and Meinert also offered a detailed classification for the family, proposing several sub-family and tribe names. Some of these reflected perceptible differences in the morphology of the species and genera, but their classification caused some subsequent confusion, and these family group names have subsequently been largely ignored. Although the descriptions and drawings may be regarded as too brief and simple by the standards of today, this does not detract from their outstanding contribution. The completion of their body of work brought the total number of species proposed to 146 in 33 genera. The comprehensive nature of their monographs is demonstrated by the fact that of the genera accepted today 35% are attributed to Schioedte and Meinert. Since 1884 only 17 genera have been described, and 16 genera are junior synonyms or otherwise invalid. The decades following Schioedte and Meinert’s work saw little sustained activity, the most significant contribution being the accumulated works of Carl Bovallius [1855–1887] describing seven cymothoid species (among other taxa). The early Twentieth Century in contrast saw considerable activity with contributions from the major isopod taxonomists of the period such as the Reverend Thomas Roscoe Rede Stebbing [1893–1923; two species], Harriet Richardson [1884–1914; 24 species], Hugo Frederik Nierstrasz [1915–1931; five species], and Herbert Matthew Hale [1926–1952; three species], the last named whose work continued past World War II. The 1970s saw the start of a period of sustained research on the family, with a number of authors working for sustained periods both regionally and globally. Slightly pre-dating this period were Thomas Elliot Bowman [1962–1983; 13 species] who published a series of detailed descriptions and redescriptions of cymothoids and Jean-Paul Trilles [1961–present; seven species] who published on diverse aspects of the Cymothoidae, and in a taxonomic context is particularly noted for his compilations of synonymies and museum holdings (Trilles, 1994). Ernest H. Williams and Lucy Bunkley-Williams [1978–2006; 27 species] were prolific in publishing on the Caribbean fauna and also that of Japan and Thailand. These authors also provided a synopsis of fish-parasitic isopods and corrected many of the problems and errors encountered in the fish-parasitic literature (Bunkley-Williams and Williams, 1998; Williams and Bunkley Williams, 2000). The late Vernon Thatcher [1988–2009; 15 species] made a huge contribution to what had been an almost unstudied region and habitat – the South American freshwaters. V.V. Avdeev [1973–1990; 15 species] and Niel L. Bruce [1982–present; 39 species] both made a significant contribution to the documentation of Indo-Pacific Cymothoidae, Bruce notably attempting to revise and restrict generic concepts within the family. Richard C. Brusca [1977–1983; 2 species] documented the Cymothoidae of the tropical East Pacific, culminating in an influential monograph (Brusca, 1981) that presented the first phylogeny and evolutionary hypothesis for the family. Regional documentation of the Cymothoidae has been highly inconsistent on a global basis. Proximity to major population centres clearly influenced progress in this regard. The major centres of post-Linnaean taxonomy were the museums and universities (parsonage in Stebbing’s case) of Europe and North America, and the Cymothoidae of those regions were consequently well documented by the Twentieth Century. The age of European expansion and empire played its part in documentation of tropical faunas, notably the Indo-Malaysian region. Since the 1970s some regions have received in-depth and specialist attention, notably the East Pacific (Brusca), the Caribbean (Williams and Bunkley-Williams), and eastern Australia (Bruce). 3 Variable morphology, generic and species synonymies – a particular challenge A particular challenge, indeed an impediment to progress on the taxonomy of the family, is the high level of variability shown by many species. In the historic period of cymothoid taxonomy it is clear that intra-specific variation became confounded with inter-specific differences. The present high level of names in synonymy attests to this difficulty. This particular difficulty is a ‘two-way street’. To give just one example, the species Mothocya melanosticta (as Irona melanosticta) had become regarded as a highly variable species, indiscriminate in host preference, occupying diverse habitats from the pelagic to inshore, occurring in all oceans; in fact, this was simply due to sustained misidentifications of what proved to be a group of nine similar looking species with narrow host and habitat preferences (see Table 3 in Bruce, 1986). M. melanosticta was shown to occur only on flying fishes (see Bruce 1986). Conversely many spurious new names were proposed on supposed differences of what later proved to be intra-specific variation; this latter situation has been a particular issue for Nerocila, as the long synonymy for Nerocila orbignyi shows (see Bruce, 1987a). The problem that this poses is that in many cases it is still highly uncertain which names are valid, which should be placed into synonymy and equally which species to bring out of synonymy. In many cases it is not possible to confirm or reject many of the literature records for many species, so distribution and patterns of host preference are often, at best, uncertain. Generic concepts remained loose, often not based on the type species, and modified as new species were discovered and placed into available genera. Genera described in the Nineteenth Century were given brief diagnoses that were evidently subsequently difficult to apply – consequently species were frequently placed incorrectly into genera, sometimes comprehensively. For example, of the approximately 60 species that had been placed in Livoneca up to 1990, most were relocated to Elthusa and Ichthyoxenus, with only three species now remaining in the genus (see Bruce, 1990). Similarly the name Irona was widely misused for what was the genus Mothocya. 4 Relationships and classification within the Cymothoidae The Cymothoidae has long been recognized as a well-unified family, nested within the group of carnivorous, commensal, micropredatory and parasitic families that now constitutes the superfamily Cymothooidea Leach, 1814. Classification within the family dates from the work of Schioedte and Meinert (1884) who proposed five family-group names. These names were subsequently used erratically or ignored. The Anilocridae and Saophridae became subsumed by the Cymothoidae as subfamilies, while the Ceratothoinae and Livonecinae were regarded as tribes. Bruce (1990) concluded that only the Anilocrinae and Cymothoinae could be recognised. Trilles (1994) in his 1994 Podromus used all of these names, though without explanation, definitions or morphological justification. Earlier Avdeev (1985) also made use of these names suggesting that the Cymothoidae consisted of two subfamilies, and a further two tribes, one being a new family-group name. These names were not explicitly defined or justified, and in large part were based on homoplasious characters of body shape or site of attachment, and found little favour with most taxonomists. As mentioned above, perception of relationships within the family was strongly driven by site of attachment – namely external or scale attaching (Fig. 2A), buccal dwelling (Figs. 2C, E, F), gill attaching (Fig. 2D) and flesh burrowing (Fig. 2B). Brusca (1981) presented a cladogram and a phylogeny of the family (Brusca, 1981, Fig 4A and B), identifying the putative ancestor as an externally attaching ‘Nerocila-like’ taxon. The externally attaching genera and part of the South American freshwater genera were sister groups to all remaining cymothoids. Brusca termed the two major groups the ‘Nerocila lineage’ and the ‘Livoneca lineage’. Livoneca (and presumably other non-specified gill-attaching genera) was considered to be the sister group to flesh-burrowing and freshwater South American taxa, the sister group to these being ‘other flesh burrowing taxa’. Bruce (1987a,b,c, 1990) redescribed and redefined the externally attaching and gill attaching cymothoids from Australian waters. By 1997 it was apparent on morphological criteria that there was a group of related genera that approximated to the ‘Nerocila lineage’ of Brusca (1981) and the Anilocrinae of Schioedte and Meinert (1883). Bruce (1987b) accepted the use of the name Anilocrinae for the externally (scale attaching) genera, giving a diagnosis to the subfamily. Bruce (1990) later revised this opinion when reviewing the gill-attaching cymothoids, observing that genera and species of what were Anilocrinae by morphological criteria also occurred on the gills (Livoneca, Nerocila lomatia, Norileca) and in the mouth (Smenispa). Furthermore one species of the otherwise gill-attaching genus Mothocya was buccal attaching and had a general body shape similar to that of Cymothoa or Ceratothoa. Bruce (1990) concluded “there still inadequate data for many cymothoid genera, it seems preferable to avoid the use of subfamily names other than Anilocrinae and Cymothoinae.” To the present day there remains little use of subfamily categories within the family. In the Twenty-first Century small molecular data sets, and data sets using unidentified taxa were analysed, giving inconsistent and probably unreliable results. For example Dreyer and Wägele (2002) using 18S sDNA; Ketmaier et al. (2008) using 16S rRNA and cytochrome oxidase I; and Jones et al. (2008) using 16S mtDNA. Given the small number of taxa, the unexpected pairings, such as Nerocila with Ceratothoa rather than Anilocra (see Ketmaier et al., 2008), should not be considered as significant. Jones et al. (2008) showed a lack of unity for a ‘Nerocila clade’, with that genus forming a clade together with Cymothoa and Olencira. Recently Hadfield (2012) reappraised the relationships of the genera of the Cymothoidae based on a morphological data set. The resultant trees revealed that the ‘Anilocrinae’ form a well-supported clade and are in a terminal position. The buccal attaching taxa (Cymothoa, Ceratothoa, etc.) also form a robust clade that is sister to the ‘Anilocrinae clade’; the gill-attaching genera are basal and did not form a clade under any constraints. There are several implications from this result: the long-held view that the gill attaching genera together derived from the purportedly Nerocila-like ‘ancestor’ is not upheld; the Nerocila-clade and Ceratothoa clade are more derived than the gill attaching and flesh-burrowing taxa. The question that then must, in our view, arise, is what would be the plausible ancestral isopod to the Cymothoidae? In our opinion the ancestor would most likely have been similar to a Corallanidae or Aegidae. The mouthparts of Rocinela, as pointed out by Dreyer and Wägele (2001) are more similar to those of the Cymothoidae than to the remaining Aegidae. Rocinela have the most flat body of the Aegidae, and adapting to living in the gill cavity is certainly plausible, as is becoming more permanently attached to the hosts. At least one species, Rocinela signata, is known to occur in the gill chamber of its host fish (Bunkley-Williams et al., 2006; Cavalcanti et al., 2012). Further more, one still has to consider that there may have been two evolutionary events leading to fish parasitism in the Cymothoidae, which within the Isopoda has occurred in several different families (e.g. Gnathiidae, Aegidae, Corallanidae, Tridentellidae and Cymothoidae). 5 Classification and relationships within the Isopoda The Cymothoidae have been regarded as part of a “lineage” (Brusca, 1981) going from the free-living scavenging and predatory Cirolanidae, through to the families Corallanidae, Tridentellidae and Aegidae showing progressively more trophic dependency as commensals and micropredators, to the obligate fish parasites of the family Cymothoidae. The then Epicaridea (now Bopyroidea and Cryptoniscoidea) were regarded as related, indeed some analyses showing them to be the sister group to the Cymothoidae, but there was a lack of clarity as to the precise degree of relatedness. These families were placed with the suborder Flabellifera. Wägele (1987) challenged this classification, and suggested (among other changes) the separation of the Cymothoida from the Sphaeromatidea. This view was not well received at the time, and the first cladistic analysis of the Isopoda by Brusca and Wilson (1991) did not support this separation. For a period there was at times acrimonious debate over isopod classification, which eventually succumbed through inertia and immovability of the different parties. Brandt and Poore (2003) developed a much larger data set than had previously been used, and further offered it widely for appraisal prior to publication. Their analysis strongly supported that the Flabellifera be abandoned and the Cymothoida and Sphaeromatidea be recognized as suborders, supporting Wägele’s original assessment, albeit based on different characters. The new resultant classification was immediately widely accepted (with little dissent). The Cymothoidae are sister group to the Aegidae or Bopyridae within the clade that is the superfamily Cymothooidea. 6 Fossil record The fossil record for the Cymothoidae is extremely poor – indeed virtually non-existent. In part this is because it is not possible to place fossil isopods without appendages into an extant family with any degree of confidence. This was demonstrated for the species Palaega lamnae, which Bowman (1971) showed could be placed equally in the Cirolanidae or the Cymothoidae. Conway Morris (1981) showed the bopyrid isopods were present back to the Jurassic era, their presence being indicated by the characteristic distortion of the carapace in fossil decapods (crabs and shrimps). It is equally probable therefore the Cymothoidae had also evolved at that point. To our knowledge no fossil isopod has been specifically attributed to the family Cymothoidae. 7 Taxonomic diversity The Cymothoidae is a large family, exceeded in the number of genera and species only by the Sphaeromatidae, Cirolanidae and Bopyridae. There are currently 40 genera with 383 species accepted (See Fig. 3 for examples of some of the different generic body forms). Sixteen genera and 83 species are in synonymy. A further seven species are regarded as Nomina dubia. The family, as is typical for most marine isopod families, is dominated by a relatively small number of large genera – such as Anilocra (49 species), Nerocila (42 species), Ceratothoa (33 species), Cymothoa (51 species), Elthusa (28 species) and Mothocya (29 species). The predominantly freshwater genus Ichthyoxenus has 24 species, while most of the remaining genera have between one and ten species, including the South American freshwater genera. 8 Hosts Cymothoids have been described from representatives of almost every single family of marine teleosts as well as a number of freshwater groups. In general there does not seem to be a specific host characteristic, whether morphology or behaviour, that influences the possibility of being parasitised by a cymothoid. In addition to parasitising teleosts, cymothoids have also been reported from chondrichthyan fishes, jellyfish, cephalopods, crustaceans, and amphibians (Trilles and Öktener, 2004; Ateş et al., 2006). Although there are within the different cymothoid genera and species varying degrees of host specificity, there exists a general trend that host specificity increases with decreasing latitude. For example, high-latitude temperate species (e.g. Anilocra physodes) use more host taxa than tropical species, where tropical species of Anilocra typically primarily parasitize fish of a single family, possibly a single genus and in some cases a single fish species (Bruce, 1987b). This might be related to the general lower cymothoid diversity in temperate regions where the low diversity possibly results in an increased number of hosts species used. The opposite might be true for the tropics where the high cymothoid diversity possibly results in competition that leads to an increasing specialization. However, the current uncertainties in species level taxonomy within the family referred to earlier (Section 3), also impacts on our knowledge of host specificity. For example, if we accept that every host record of Ceratothoa trigonocephala is correct then we will conclude that it parasitises at least 18 species in 17 genera and 14 families of fish hosts. Recent work by our group actually shows that the majority of these host records are due to incorrect identification of the cymothoid and not because this species parasitises a wide range of hosts (Hadfield et al., 2014a). Incorrect host identification further confuses the matter making accurate host records scanty. Another interesting aspect of cymothoid-host interaction is their specific site of attachment, which seems to be very consistent within species and sometimes genus specific. Bowman and Mariscal (1968) found that the attachment position of Renocila heterozota on Amphiprion akallopisos was always on the anterior trunk region, just behind the head. Likewise, Morton (1974) showed the attachment site of Nerocila phaeopleura is overlying the lateral line in the posterior third of the body. Morton (1974) further suggested that site specificity is determined by the needs of the parasite and the limitations exerted by the morphology and habits of the host. Fish infested by cymothoids have been described as suffering from localised damage or lesions, reduced growth and condition index, host behavioural problems and in extreme cases death (Romestand and Trilles, 1979; Brusca, 1981; Grabda and Rokicki, 1982; Colorni et al., 1997; Horton and Okamura, 2001; dos Santos Costa and Chellapa, 2010; Rameshkumar and Ravichandran, 2014). Impaired reproduction and a reduced lifespan in some hosts have also been observed (Adlard and Lester, 1994). Depending on the particular species and its location on the host, a number of negative effects can be observed on the fish host (Trilles, 1994), namely: buccal species cause tongue degeneration (Romestand and Trilles, 1979; Brusca and Gilligan, 1983), skull deformations (Trilles, 1994) and teeth problems (Romestand and Trilles, 1979); gill parasites cause gill and branchial filament damage (Kroger & Guthrie, 1972), pericardial cavity and heart decompression, and reduced respiratory metabolism (Trilles, 1994). External parasites can cause partly degenerating fins, particularly near the site of attachment (Bowman and Mariscal, 1968; Brusca, 1978) and damage to the scales and epidermis. Physiological modifications of the chimic composition of the fish plasma (Romestand and Trilles, 1979; Horton and Okamura, 2003) have been observed, and in many instances buccal and surface parasites have affected growth rate (Trilles, 1994). The sustained aerobic swimming speed and the swimming endurance of parasitised fish at high-water speeds was also found to be reduced due to the drag of the external isopod (Östlund-Nilsson et al., 2005). However, there have also been a number of studies where no obvious or recordable harmful effects were observed (Brusca, 1981; Landau et al., 1995). Östlund-Nilsson et al. (2005) proposed that the apparent lack of change in the condition of infested hosts may be a result of infested hosts feeding more and more often than non-parasitised hosts, in order to compensate for the high rate of energy loss. Interestingly, it appears as if populations of the same cymothoid species can have either a negative impact or no effect at all, depending on which host they infest. This can be seen on the East Coast of the United States where Livoneca ovalis cause growth inhibition of young white perch, (Sadzikowski and Wallace, 1974) as well as erosion of gill filaments and flared opercula recorded from bluefish (Meyers, 1978), but have no apparent damage or effect on the growth of the young-of-the-year bluefish, Pomatomus saltatrix, in a nearshore environment (Landau et al., 1995). 9 Reproduction and life cycle The life history and its cycle for most individual cymothoid species is poorly known or documented. One of the main difficulties arises from keeping these parasites in laboratory conditions and monitoring their growth, especially if the parasite resides inside the host. Similarly, in the field there is the problem of recognising the same fish host as markings can fade and fin clips or wounds can heal. Similar to other isopods, the adult female cymothoid is known to carry the developing embryos in the marsupium. This pouch protects the young and keeps the embryos aerated with its oostegites (Varvarigos, 2003). The eggs hatch in the marsupium and undergo their first moult into the pullus stage, which are sexually non-differentiated. The first pullus (pullus I) is only found in the marsupium where it will moult into the second pullus (pullus II) which has six pairs of pereopods armed with dactyli and a strongly pigmented cuticle. Sexual differentiation occurs only after the young have left the brood pouch in search of a host. These young and active isopods (now termed manca) are well equipped for swimming with long setae on the margins of the appendages and well developed eyes. They can remain free swimming for several days feeding on yolk stores (Brusca, 1978) and are capable of leaving a host provided they have not moulted into the following stage. Mancas will seek an appropriate host on which to attach and, once found, will moult and lose their swimming setae, becoming immotile. After permanent attachment is complete, a subsequent moult follows where a seventh segment and pair of pereopods appear and the isopod is in a pre-adult form. The isopod is now referred to as a juvenile which will function as a male until circumstances require it to transform into a female. The transformation of the male into the female is a complex process and is dependent on many factors including the presence of other individuals, especially other females which would prevent the transformation (Lincoln, 1971). Sexual transformation occurs as the male organs regress and the female reproductive apparatus develops and becomes more dominant. Once fully female, the isopod is known as an adult. Little information is available on the duration of one cycle which can range from 62 days in Anilocra pomacentri (see Adlard and Lester, 1995) to one year for Glossobius hemiramphi (see Bakenhaster et al., 2006). To fully understand the potential impact of these parasites on aquaculture more studies are needed on the life cycles and reproduction of cymothoids. 10 Biogeography Only when mapping the distribution of the marine cymothoids using Spalding et al.’s (2007) Marine Ecoregions of the World (MEOW) can one really appreciate their skewned global distribution (Fig. 4, data from Poore and Bruce, 2012). It is clear that the highest diversity resides within the tropical regions with the Central Indo-Pacific realm hosting almost double the number of species than any other realm. What is interesting to note is that although 41 species have been recorded from the Tropical Atlantic realm, the vast majority are from the Western Atlantic (see Williams and Williams, 1981, 1982, 1985 to cite a few) and almost nothing from the Eastern Atlantic (off Africa). Although there is no doubt that the highest biodiversity of cymothoids are indeed in the tropics, the low number of species recorded from the temperate regions might rather be a reflection of the focus of researchers that have been working on this group rather than their actual distribution. It is clear from Section 2 that the main focus of the researchers that contributed the most to species descriptions was on the tropical fauna. For example Poore and Bruce (2012) reported only two species from the Temperate South African realm, but recent focused research by Kerry Hadfield and colleagues from this region showed that this number have the potential to increase fivefold (Hadfield et al., 2010, 2011, 2013, 2014a,b). No clear distribution pattern is apparent for the freshwater cymothoids where the majority (approximately 13 species) are known from the Amazon region of South America (Thatcher et al., 2003, 2009) followed by six species distributed from various localities in Asia and only four from central Africa (Brusca, 1981). 11 Human issues The occurrence of cymothoids in natural populations is often irregular and the levels of prevalence and distribution extremely variable (Brusca, 1981). Infestations prevalence of up to 73% by Ceratothoa spp. and Cymothoa spp. in natural populations (see Horton and Okamura, 2002; Horton et al., 2005; Hadfield et al., 2013) can be considered as very high, however it can increase to 98% on fish kept in farming facilities (Sievers et al., 1996). Other occurrences of cymothoids in aquaculture are also very high, causing mass mortalities in cultured fish (Horton and Okamura, 2001, 2003; Mladineo, 2002, 2003; Rajkumar et al., 2005a,b). In the majority of cases, fishes infested by cymothoids in aquaculture are not those traditionally recorded as the natural host. Papapanagiotou et al. (1999) therefore, proposed that the cultured fishes are only parasitised due to infested wild fish (which are the natural hosts) coming in close contact with the cultured fish and transferring their parasites. Horton and Okamura (2001) further supported this idea as none of the cymothoid isopods they reported from aquaculture conditions are known to parasitise the same species in the wild. Crustacean fish parasites are very difficult to remove from fish culture facilities. However, transmission of the parasite could be prevented by using small-sized mesh nets around the cages to hinder the swimming larvae from getting to the fish (Rajkumar et al., 2005a). Other management practices include changing fouled nets, placing the cages in stronger currents, lowering the water temperatures and placing them in greater depths to discourage the isopods who seem to thrive with the opposites of these conditions (Papapanagiotou et al., 1999; Papapanagiotou and Trilles, 2001). The use of a large variety of chemical treatments against cymothoids in aquaculture has also been tested with successful treatments having little or no adverse effects on the fish hosts and no reinfections. Certain insecticides (Sievers et al., 1995; Athanassopoulou et al., 2001) and formalin baths (Williams, 1974) are among those treatments on specific cymothoid and host species and at specific concentrations. However, these chemical treatments are not always effective and occasionally the adult stages seem to be little affected by the chemical treatments (Papapanagiotou and Trilles, 2001), or conversely attempts to eliminate the parasite will often result in damage to the host fish (Sievers et al., 1995). 12 Conclusion Sampling for cymothoids presents unique problems. Unlike free-living isopods, where specific taxa can be targeted with reasonable expectation of success, it is simply not possible to acquire a broad range of cymothoid genera in a single survey through direct collecting. Use of micro-spears with SCUBA adequately targets the externally attaching genera only. Cymothoidae, other than the scale-attaching taxa, can be obtained directly in small numbers and on an opportunistic basis, or indirectly via museum collections, fishers and fishing organisations or by joining fish trawlers, research or commercial, and examining the by-catch. Infestation rates are often low, and discovery of sites where there infestation rates are in the 5–10% category is rare, and usually opportunistic, such as checking fish landing sites. Combining all these methods can produce good material for morphological systematics, but the range of taxa that can be used for molecular analysis is inevitably very limited. Three or four regions can be considered as well known or moderately well-known from the taxonomic perspective. These are the Central Indo-Pacific, the overlapping region of eastern Australia, the Caribbean and the South American freshwater taxa of the Amazon River and its tributaries. Typically these well-known regions are those that have received attention from specialist taxonomists focused on the Cymothoidae. Cymothoids decrease rapidly in diversity from the tropics to temperate and cold waters. While some of these areas such as the North Atlantic, New Zealand or northern East Pacific have relatively low diversity, the isopod faunas of these areas are well known. In contrast there are several major regions were documentation remains minimal, these regions are both seaboards of South Atlantic, the Eastern and Western Indian Ocean and the Eastern Indo-Pacific. Tropical coral reefs, that is living reef, are by their nature difficult to sample by mass collecting methods. Photographs from amateur and professional photographers suggests that a great diversity of small fish species will have associated cymothoids, but these specimens have yet to find their way into collections or to taxonomists. Brusca (1981) noted that the Cymothoidae is “taxonomically the least understood family within the suborder Flabellifera and is one of the most troublesome of all isopod taxa with which to work”. The many challenging aspects of the family, from collection to identification, account for the Cymothoidae being rarely studied, with only a handful of cymothoid specialists worldwide. Brusca’s (1981) statement is still relevant more than 30 years later and future studies regarding their ecology, taxonomy, lifecycle and molecular studies are still required in order to present a complete understanding of this economic and ecological important taxon.
Author and article information
Journal
Journal ID (publisher-id): nau
Title:
Nauplius
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Nauplius
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Sociedade Brasileira de Carcinologia
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2024
Volume: 32
Electronic Location Identifier: e20240530
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[1]
São Cristóvão
orgnameUniversidade Federal de Sergipe
orgdiv1Programa de Pós-Graduação em Biologia Parasitária
Brazil
[2]
Aracaju
Sergipe
orgnameCompanhia de Desenvolvimento dos Vales do São Francisco e Parnaíba
Brasil
Article
Publisher ID: S0104-64972024000100205 Publisher ID: S0104-6497(24)03200000205DOI: 10.1590/2358-2936e20240530
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November
2023
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: 04
January
2024
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