~ 331 ~ International Journal of Fisheries and Aquatic Studies 2015; 2(4): 331-336 ISSN: 2347-5129 IJFAS 2015; 2(4): 331-336 © 2015 IJFAS www.fisheriesjournal.com Received: 12-12-2014 Accepted: 21-01-2015 Oden Esther M Zoology and Environmental biology, Parasitology unit, University of Calabar, Calabar, Nigeria. Ama–Abasi Daniel Institute of oceanography and Marine Sciences, University of Calabar, Calabar, Nigeria. Ndome Chris Zoology and Environmental Biology, Fisheries and Aquaculture unit, University of Calabar, Calabar, Nigeria. Correspondence Oden Esther M Zoology and Environmental biology, Parasitology unit, University of Calabar, Calabar, Nigeria. Incidence of nematode parasites in snakehead, Parachanna obscura of the lower Cross river system, Nigeria Oden Esther M, Ama–Abasi Daniel, Ndome Chris Abstract The incidence of nematode parasites in African snakehead, Parachanna obscura of the lower Cross River system was investigated. The objective was to determine the prevalence and intensity of the infection with size, gender and season of the fish species. A total of 510 specimens of Parachanna obscura was sampled from July 2009 to January 2010. The fish were processed through standard parasitological manipulations. There was 53.9% prevalence of infection and mean intensity of 8 nematodes per fish in the Great Kwa River. In the Cross River 96 fishes were infected with a total of prevalence and mean intensity was highest in the lower length-classes. Mean intensity was lower in females than in males due to their reproductive requirement. Generally, there was no significant difference in prevalence by size and gender at p > 0.05. Mean intensity and nematode abundance, were higher in Great Kwa River than the Cross River. There was no correlation between the total numbers of nematodes and the infected P. obscura by size and gender. The prevalence of infection by season in Great Kwa River was variable; with a mean intensity of 12 worms per fish in dry season and 6 worms per fish in wet season. The low level of helminthes infection in Parachanna obscura means that it is safe as aquaculture candidate and this should be vigorously pursued. Keywords: Nematodes, Parachanna obscura, Size, Gender, Season, Lower Cross River system. 1. Introduction African snakehead, Parachanna obscura is an emerging candidate for aquaculture. The species is known to have sweet flesh with highly acceptable market value [1] . It is one of the subsistence species in the Cross River system and good food condiments for the people of the Cross River Basin. There is an ongoing screening of the species for aquaculture because of its hardiness, good quality fillet, and high nutritional value. Ama-Abasi et al., [1] reported high proportion of protein and fats for varying nutritional and energy requirements for people with different health challenges. Previous work on the species include Ama-Abasi and Ogar [2] on proximate composition, Ama-Abasi and Affia [3] on food and feeding habit, Adebayo and et al [4] on haematological profile of the species. On the other hand the greatest setback to aquaculture and its growth has been fish parasites and diseases [5, 6] . African snakehead and other fish species are known to be hosts of parasites and diseases. Akinsanya et al., [7] reported on parasites of Parachanna obscura, from Lekki Lagoon, Lagos to include two helminthes, Procamallanus sp (Spirocamallanus) and Contracaecum sp and a trematode, Clinostomum metaceria, with prevalence of 5.9%. There is no documented evidence of snakehead parasites in the Cross River system in spite of the fact that snakehead fishery is popular and all year round in the river system with a significant economic interest. It was the objective of this study therefore to ascertain the incidence and prevalence of nematode infection of Parachanna obscura from the lower Cross River system as a further screening of its aquaculture potentials. 2. Materials and Methods 2.1 Study area The Cross River system is formed from numerous tributaries arising from the western slopes of the Cameroun Mountains which have two spurs into Nigeria as the Oban Hills in the south and the Obudu Hills in the north. When the main river enters Nigeria from the Cameroun, it flows first in a westward direction and then turns southwards and enters the Atlantic Ocean