Seasonal and Spatial Distribution of Nematode Larvae of the Genera Anisakis and Contracaecum (Anisakidae) in Two Populations of Mugil Cephalus (Mugilidae) from Saloum and Senegal Rivers

Abstract

Anisakis sp. and Contracaecum sp. are nematodes belonging to the family of Anisakidae. They are worldwide distributed and use a great number of fish species as intermediate, paratenic or final host. Despite their effects on fish and human beings, they play ecological role as biological tags to identify fish population or bioindicators of marine pollution. From January to December 2009, the helminthological examinations of 129 and 167 specimens of Mugil cephalus originating from Saloum and Senegal estuaries respectively revealed the presence of Anisakis sp. and Contracaecum sp. larvae. Generally, whatever the season or locality, the kidney lodges more larvae of Anisakis sp. than the liver or the general cavity. All Contracaecum sp. larvae were found in the mesentery of Mugil cephalus whatever the locality and season. In each locality, the prevalence of Anisakis sp. larvae was higher in rainy season than in dry season whereas the larvae of Contracaecum sp. were more frequent in dry season than in wet season. Mean intensity of the Anisakidae larvae showed significant differences according to the season in the estuary of Saloum and non significant variation in the estuary of Senegal. The mean abundance of these larvae varied significantly depending on the locality, the season or the site of infection. These results are explained by factors related to the host (fat content in infested organs), factors in relation to the environment (temperature, salinity) and the presence of birds, final hosts. In the Saloum estuary, Anisakis sp. was dominant in rainy season, while Contracaecum sp. dominates in dry season. However, in the estuary of Senegal, Anisakis sp. was dominant all the year. So we can say that Anisakis sp. is characteristic of the estuary of Senegal while Contracaecum sp. is characteristic of the Saloum estuary. Distribution of anisakidae larvae is more related to the locality, the season and the site of infection rather than the fish gender.