Prevalence of Cymothoidae (Isopoda) Infestation in Bigeye Scad (Selar crumenophtalmus) from Batangas, Philippines

Cymothoid isopod research is relatively scarce in the Philippines, despite the local economic significance of bigeye scad as an inexpensive source of protein and other nutrients. Isopod parasitism has also been shown to have detrimental effects on their fish hosts. The current study aimed to define the host-parasite relationship between cymothoid isopod and bigeye scad by determining cymothoid isopod prevalence, intensity, and host-parasite length correlations in bigeye scad (Selar crumenophthalmus) hosts sourced from Batangas, Philippines. Fish samples were sampled from the Tagaytay City Market in Cavite, which sources fish directly from Batangas. Fish samples were immediately measured and inspected for isopods in the branchial and buccal cavities. Isopods found were extracted, measured, and preserved in ethanol for identification. The isopods were identified as cymothoid isopods and consisted mostly of Norileca indica specimens and one Glossobius impressus. Prevalence and mean intensity of cymothoid isopod infections in bigeye scad were 30% and 1.6, respectively. A possible correlation between isopod size and host size was speculated for non-ovigerous female isopods, but data for male and ovigerous female isopod specimens were inconclusive. The host-parasite size relationships between bigeye scad and isopods are less likely based on body size of either the host or the parasite and are more likely based on other factors such as host cavity size.