WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2013 51 were quite abundant and were present on and in each organ studied. However, Hossain et al. (2008) reported the dominance of Trichodina rather than trematoda. The most probabale reason for these site-specific variations might be seasonal fluctuations and climatic variation, which demand further research. Protozoa crustaceans and trematoda were dominant on skin while digenea and nematodes were totally absent. The number of protozoans and trematodes decreased as fish size increased (Table 1), while trematodes decreased (Table 4). Farhaduzzaman et al. (2010) observed ten species of parasites, seven of which were ectoparasites. In our study, the number of ectoparasites was always higher than endoparasites because of the easy accessibility and availability of more surface area for attachment, further confirming that skin is the primary organ attacked by parasites. Generally trematodes occur at a higher frequency than protozoa, irrespective of season. Smaller rohu are more susceptible to parasitism because they cannot support a parasite burden and succumb to death earlier than larger fish (Krist and Lively 1998). Weaker and stressed fish were always more susceptible and provided an ideal place for parasites to live and flourish. Nevertheless, it was not clear which happens first, stressed fish or parasitic attack. The most prevalent parasites in both gut and liver were nematodes and trematodes. Guts of all samples had greater loads of parasites than livers (Table 4 and 5). No other parasite or any developmental stage was visible in any sample, irrespective of site. Rohu is herbivorous; hence, a true stomach is not present. The anterior part of the alimentary canal is swollen to form a sac behind the esophagus, which serves as a place for food storage (Khanna 1975). Therefore, most gut parasites inhabit the anterior part of intestine. Heavy infestation of both nematodes and trematodes occurred in the intestine. The region around the pyloric sphincter in vertebrates is physiologically favorable to the majority of helminthes, inasmuch as it is relatively calm and rich in highly nutritive food material (Chauhan et al. 1981). Fishes infected with Capillaria (Hepatocapillaria) cichlasomae eggs usually contain huge number of eggs in the liver (Moravec TABLE 1. Parasitic load on skin. Fish weight (g) Protozoa Crustacea Digenea Nematoda Trematoda 1-20 1.1±1.1 0.5±0.6 0 0 1.1±1.3 21-40 0.7±1.0 0.8±0.8 0 0 1.4±1.5 41-60 0.6±0.8 0.8±0.9 0 0 0.4±0.7 61-80 0.7±0.7 0.7±0.8 0 0 0.9±1.1 TABLE 2. Parasitic load on gills. Fish weight (g) Protozoa Crustacea Digenea Nematoda Trematoda 1-20 0.7±0.8 0 0 0 0.8±1.2 21-40 0.6±0.7 0 0 0 0.9±1.2 41-60 0.8±1.1 0 0 0 0.7±0.8 61-80 0.3±0.5 0 0 0 0.9±1.0 TABLE 3. Parasitic load in peritoneum. Fish weight (g) Protozoa Crustacea Digenea Nematoda Trematoda 1-20 0.5±0.6 0 0 0.6±0.9 0.8±0.8 21-40 0.6±1.1 0 0 0.4±0.7 0.6±0.8 41-60 0.6±0.9 0 0 0.8±1.0 0.7±0.8 61-80 1.0±1.2 0 0 1.0±0.0 0.8±0.9 TABLE 4. Parasitic load in gut. Fish weight (g) Protozoa Crustacea Digenea Nematoda Trematoda 1-20 0.2±0.4 0 1.3±1.8 2.3±1.9 1.9±1.6 21-40 0.1±0.4 0 0.7±1.1 2.3±2.0 2.0±1.9 41-60 0.4±0.7 0 0.6±1.0 2.4±1.8 1.6±1.8 61-80 0.4±0.5 0 0.5±1.0 1.5±1.3 1.3±1.1 TABLE 5. Parasitic load on liver. Fish weight (g) Protozoa Crustacea Digenea Nematoda Trematoda 1-20 0 0 0 0.6±0.9 0.7±0.9 21-40 0 0 0 0.4±0.7 0.3±0.6 41-60 0 0 0 0.5±0.8 0.6±0.7 61-80 0 0 0 0.5±0.8 0.5±0.6 (CONTINUED ON PAGE 53)
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