Prevalence of Parasitic Infestation in Freshwater Crab, Sudanonautes africanus (A. Milne-Edwards, 1869) (Brachyura: Potamonautidae) from selected Rivers in Edo and Delta States of Nigeria

Abstract

Freshwater crabs support fishery resources and serve as intermediate host to the major groups of animal parasites, hence, this study investigates the prevalence and intensity of parasitic infestation in freshwater crab Sudanonautes africanus, and its relationship to carapace width (CW) by collecting 350 specimens between March, 2007 and January, 2010 from selected rivers in Edo and Delta States. The results showed that a total of 174 (49.71%) individuals were infected with immature stages of nematode and digenean parasites in the 4 study sites. The prevalence of 86.54% was recorded in Iyi-Ekwu River, 65.74% in Oke River and 30.36% in Ikpoba River. However, the least prevalence of 18.18% was recorded in Orogodo River. Data analysis by Kruskal-Wallis, one-way ANOVA reveals there was no statistically significant difference (p>0.05) in prevalence among the four sampling sites. A total of 166 (47.43%) individuals from the four study sites were infected with larval nematodes, while 8 (2.29%) were infected with juvenile trematodes from both Oke and Orogodo Rivers. Result obtained from unpaired t-test indicates that crabs measuring 4 to 6 cm CW had a significantly higher prevalence (p<0.05) of parasitic infections. Furthermore, the intensity of nematode larvae isolated from each crab ranges from 1-25 (mean 5), 1-3 (mean 2), 1-4 (mean 2.3) and 1-6 (mean 2.8) nematodes per crab in Rivers Oke, Ikpoba, Iyi-Ukwu and Orogodo, respectively. The length of nematode larvae ranged from 0.7mm – 6mm long with a mean length of 2.4mm. Studies are on-going to experimentally obtain adults of the nematode larvae and juvenile trematodes for species identification.

Keywords: Carapace width, Freshwater crab, Intensity, Nematode, Prevalence, Trematode