BIOLOGY AND HOST-PARASITE 



RELATIONSHIPS OF CYMOTHOA EXCISA 



(ISOPODA, CYMOTHOIDAE) WITH THREE 



SPECIES OF SNAPPERS (LUTJANIDAE) 

 ON THE CARIBBEAN COAST OF PANAMA 



Although parasitic isopods of the family Cymo- 

 thoidae have been described from both freshwater 

 and marine fishes, relatively little is known of 

 their biology and host-parasite relationships 

 (Morton 1974). Probably all species of cymothoids 

 are protandrous hermaphrodites, with the male 

 larvae settling out of the plankton onto the mouth, 

 body surface, body cavity, or gills of their host. 

 After a period of maturation, males of some species 

 become associated with the buccal cavity where 

 they undergo a sex change. Both broad and limited 

 host specificities have been described for members 

 of the Cymothoidae (Trilles 1964). 



Here we comment on the biology and occurrence 

 of Cymothoa excisa Perty on three sympatric spe- 

 cies of Caribbean snappers: Lutjanus synagris 

 (Linnaeus), L. analis (Cuvier), and Ocyurus chry- 

 surus (Bloch). Host-parasite relationships and in- 

 festation rates are discussed and evidence is pro- 

 vided suggesting that this parasite does little, if 

 any, damage. 



Methods and Materials 



All specimens were collected along the Carib- 

 bean coast of the Republic of Panama and the 

 Canal Zone, near the Smithsonian Tropical Re- 

 search Institute's Galeta Marine Laboratory. 

 Samples were taken in sea grass habitats consist- 

 ing primarily of Thalassia testudinum, using a 

 4.9-m otter trawl with 1.3-cm bar mesh. Details of 

 the trawling program and site descriptions are 

 given in Heck (in press). All material was sorted in 

 the laboratory and subsequently preserved in 10% 

 Formalin. 1 



Fishes from which parasites had been removed 

 were wet weighed after blotting. Standard lengths 

 of fishes were measured to the nearest 0.5 mm, and 

 total lengths and widths of isopods were measured 

 to the nearest 0.01 mm, using dial calipers. Indi- 

 vidual isopods were sexed according to the pre- 

 sence of an appendix masculina on the second 

 pleopod (males) or from the development of ooste- 

 gites and presence of larvae (females). The Mon- 



1 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



talenti femininity index |F. I. = W/L x 100, where 

 W = width and L = length (Montalenti 1941)] was 

 used for the isopods as a measure of the degree of 

 transformation from male to female. 



Fulton's coefficient of condition [K = W/L 3 , 

 where W = wet weight and L = standard length 

 (Ricker 1971 )] was used to assess the well-being of 

 fish in relation to the presence or absence of iso- 

 pods. Values of K were computed for 30 infested 

 and 30 isopod-free individuals in each of the three 

 species of snappers, L. synagris, L. analis, and O. 

 chrysurus. An arc-sin transformation was per- 

 formed on K values before statistical analyses 

 were carried out. 



Results and Discussion 



Cymothoa excisa was found to occur on 4.7% 

 (32/681) of the L. synagris, 10.5% (16/152) of the 

 L. analis, and 2.1% (11/527) of the O. chrysurus 

 collected. Adults of the two snapper genera exhibit 

 different habitat preferences: members of the 

 genus Lutjanus prefer near-bottom habitats with 

 ample cover, while O. chrysurus inhabits the 

 open-water column above coral reefs. Juveniles of 

 all three species are commonly associated with sea 

 grass beds, and it may be during this stage of their 

 life cycle that infestation occurs. This is suggested 

 by the occurrence of metamorphosed parasites in 

 very small fish (20-30 mm SL). In addition, a 

 linear relationship exists between lengths of the 

 isopod and those of its host (Figure 1), which 

 further suggests that fishes are infested early in 

 life with subsequent growth by both host and 

 parasite. Six male parasites differed significantly 

 from this relationship, however, and each of these 

 occurred jointly (or in triplicate) with a much 

 larger female. Previously, Bowman (1960) re- 

 ported that pairs of isopods (Lironeca puhi Bow- 

 man) were nearly always present in the gill cavity 

 of the moray eel Gymnothorax eurotus (Abbott). In 

 our specimens, pairs (or triplicates) were found in 

 only 6.8% of the parasitized fishes and during sort- 

 ing no free isopods were found which might have 

 escaped from the mouth cavity. Unless male 

 isopods were differentially lost during the trawl- 

 ing operations, it appears that the population biol- 

 ogy of cymothoid genera can be quite different. 



Several other species of lutjanids collected 

 showed no indication of isopod infestation. For 

 example, none of the 53 Lutjanus griseus (Lin- 

 naeus) nor any of the 19 L. apodus (Walbaum) 

 contained C. excisa. Differences in habitat prefer- 



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