49 Indian J. Fish., 61(1) : 49-56, 2014 Occurrence of the isopod, Norileca indica (Isopoda: Cymothoidae) on bigeye scad, Selar crumenophthalmus (Bloch) off Mumbai coast, India TAMBIREDDY NEERAJA, GAYATRI TRIPATHI AND UMMEY SHAMEEM * Central Institute of Fisheries Education (ICAR), Panch Marg, Off Yari Road, Versova, Andheri (W) Mumbai - 400 061, Maharashtra, India * Department of Zoology, College of Science and Technology, Andhra University, Visakhapatnam – 530 003 Andhra Paradesh, India e-mail:tambinee@yahoo.com ABSTRACT Parasitological investigations on the occurrence of isopod parasites in carangid fish species collected off Mumbai coast (south-west coast), Arabian Sea, India was carried out for a period of one year from March 2012 to February 2013. Altogether seven fish species were examined viz., Atropus atropos (Bloch & Schneider, 1801), Caranx sexfasciatus Quoy & Gaimard, 1825, Decapterus russelli (Rüppell, 1830), Megalaspis cordyla (Linnaeus, 1758), Selar crumenophthalmus (Bloch, 1973), Scomberoides commersonnianus Lacepède, 1801 and Scomberoides tol (Cuvier, 1832), but only S. crumenophthalmus was found to be infested with the cymothoid isopod parasite Norileca indica (Milne-Edwards, 1840) Bruce, 1990. During the study period, live specimens of male and female N. indica were isolated from the branchial cavities of the bigeye scad, S. crumenophthalmus. Out of the 290 specimens of S. crumenophthalmus examined, 114 were found to be infested with N. indica. The body size of females (N=10) was 24 to 35 (29.70 ± 3.71) mm long and 11 to 16 (13.30 ± 1.57) mm wide at pereonite 4, while the males (N=10) were 15 to 21 (17.20 ± 2.35) mm long and 6 to 8 (6.50 ± 0.71) mm wide at pereonite 4. The isopods were positioned in the branchial cavity of fish with their ventral side facing the inner surface of the operculum. Body of the female parasite twisted to right side in the left branchial cavity, and vice versa. The overall prevalence, mean intensity and mean abundance of infestation with N. indica were found to be 37.94%, 1.38 and 0.51 respectively. The prevalence and abundance of infestation was significantly (p<0.05) higher during post-monsoon months. Significantly (p<0.05) higher prevalence and abundance of infestation was observed in female hosts than in males. However, mean intensity of infestation was non-significant between the months and host sex. Host size does not seem to affect the prevalence, mean intensity and abundance of isopod infestation. The present finding is the first report on the infestation of N. indica in S. crumenophthalmus from Indian waters. Keywords: Cymothoidae, India, Isopoda, Norileca indica, Selar crumenophthalmus Introduction Cymothoid isopods (Crustacea: Isopoda: Cymothoidae) are hematophagous, protandrous hermaphrodites, mostly parasitic on tropical marine fishes (Brusca, 1981; Bruce, 1990; Raibaut and Trilles, 1993; Trilles, 1994; Trilles et al., 2011). They are highly host and site specific (Bunkley-Williams and Williams, 1998). Their life cycle is holoxenic, involves single host (Trilles, 1994; Ramdane et al., 2007). The larval development occurs in the brood pouch of female isopod and the juveniles are released into the water, which in a short period of time will attach to the host, reach the specific site (skin, buccal cavity, branchial cavity or body cavity), loose the swimming setae and metamorphose to males (Bunkley-Williams, 1984). The first male to parasitise the fish converts into a female and the others will remain as males, as the pheromone or neurohormone released by the female will inhibit the sex change of the males (Brusca, 1981; Bunkley-Williams and Williams, 1998; Ravichandran, 2009). About 330 species of cymothoid isopods were reported worldwide (Trilles, 1994), but only around 56 species are recorded from India (Rameshkumar et al., 2012). Most of the reports on marine cymothoidae in India are from east coast and such studies are very few on west coast (Trilles et al., 2011). Further, despite the commercial importance of carangids in Indian fishery, only two fish species were investigated for isopod infestation so far (Trilles et al., 2011, 2012; Rameshkumar and Ravichandran, 2013). Hence, in view of dearth of knowledge on isopod infestations in the marine fishes, an investigation has been undertaken on isopod parasites infestations in seven species of carangids from south-west coast of India (off Mumbai coast). In this study, a cymothoid isopod Norileca indica (Milne-Edwards, 1840) Bruce, 1990 was found infesting the branchial cavities of big-eye scad, Selar crumenophthalmus (Bloch, 1793). The present study represents the first report on the occurrence of N. indica in carangid fish from Indian waters. The occurrence of N. indica on bigeye scad in relation to month, host sex and size were investigated.