25 



E 

 E. 



i 

 t— 

 : 



20 



w 10 

 < 



< 



Q. 



• L. synagns 



* O. chrysurus 

 o L analis 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 

 FISH LENGTH (mm) 



FIGURE 1. — Relationship between Cymothoa excisa and lutjanid 

 lengths. Least squares line was fit excluding the six points which 

 fall far below the cluster of other points. These six points repre- 

 sent males which occurred jointly with females. 



ences may be responsible for the absence of cymo- 

 thoids on these species. It is also possible that 

 nonparasitized snapper species are cleaned of 

 parasites by cleaner fishes and decapod crusta- 

 ceans on nearby reefs. 



All isopods were attached to the tongue and 

 oriented anteriorly with smaller males positioned 

 behind females. Some degeneration and possibly 

 some scar tissue were evident at the base of the 

 tongue, but not elsewhere in the mouth. The 

 mouth parts of C. excisa seem adapted for piercing 

 and sucking and Morton (1974) has postulated 

 that cymothoids are hemophages. As expected, 

 females of C. excisa are proportionately wider 

 than males, and the transition from male to 

 female appears to occur in the 13- to 19-mm size 

 range (Figure 2). 



Bowman (1960) presented evidence that the 

 presence of a female suppresses feminity in cooc- 

 curring males, as expressed by the Montalenti in- 

 dex. We found just the opposite result: males oc- 

 curring jointly with females displayed a sig- 

 nificantly higher average femininity index than 

 males which occurred alone (Figure 2); U-test, 

 P<0.01). The reason for this difference is un- 

 known. 



Because C. excisa filled so much of the mouth 

 cavity of infested snappers, it seemed, a priori, 

 that the presence of isopod parasites must inter- 

 fere with feeding. However, several crustacean 



families, including Xanthidae {Micropanope sp., 

 Pilumnus sp., Panopeus sp.), Porcellanidae (Pet- 

 rolisthes sp.), Squillidae (Squilla sp.), Penaeidae 

 (Penaeus sp.), and Alpheidae (Alpheus sp.), were 

 represented in the gut contents of the infested 

 snappers. Moreover, there were no significant dif- 

 ferences between coefficients of condition calcu- 

 lated for parasitized and unparasitized fish in any 

 of the three lutjanids (/-test, P = 0.01). Thus it 

 appears that any harmful effects due to the pre- 

 sence of parasites are not reflected in either the 

 ability to capture prey or in overall health, as 

 measured by K. It is possible, however, that the 

 presence of isopod parasites may lower fitness by 

 causing increased mortality during periods of 

 stress (Keys 1928), by reducing the reproductive 

 output of infested fish, or by decreasing the ability 

 of parasitized individuals to avoid predators. Al- 

 though the requisite data are lacking to test the 

 first two premises, we were able to test the latter 

 possibility indirectly using the following reason- 

 ing: If predation is not selective for parasitized 

 individuals, then a similar distribution would be 

 expected for each group. This was tested by assign- 

 ing both parasitized and nonparasitized individu- 

 als of all three species to 20-mm (SL) size classes 

 for all but the largest fish (excluded because of 

 small sample size). There was no significant dif- 

 ference between the two groups (x 2 = 6.69, P = 

 0.05). 



LU 



LU 



2 4 6 8 10 12 14 16 18 2022 24 26 

 LENGTH (mm) 



FIGURE 2. — Femininity index in Cymothoa excisa. Legend: * 

 male, • = female, o = male occurring jointly with female, *? 

 sex indeterminate. 



876 



