Trophic involvement of phytoplankton in the food bolus of three developmental stages of Oreochromis niloticus (Linnaeus, 1758) in aquaculture

The composition of stomach contents of three developmental stages of Oreochromis niloticus in intensive rearing was determined at the Research Station on Continental Fisheries and Aquaculture of Bouaké (SRPAC-Bouaké, Center of Côte d'Ivoire). The objective of this study was to know the phytoplankton consumed and its proportion ingested by this species in spite of the exogenous food intake. The phytoplankton composition of stomach contents was determined by analyzing the stomachs of 150 specimens including 50 fry, 50 fingerlings and 50 adults. The vacuity coefficient was 28%, 16% and 24% respectively following the same order. The relative importance index (IRI) of prey items allowed the identification of the most important taxa in the food bowls of Oreochromis niloticus and to evaluate their contribution. Thus, Scenedesmus quadricauda, Phacus orbicularis and Pediastrum duplex are the fry preferred prey, Dictyosphaerium pulchellum for fingerlings and Phacus orbicularis and S. quadricauda for adults. In addition, Cyanobacteria with toxinogenic potential such as Cylindrospermopsis raciborskii, Anabaena circinalis, Anabaena cf. spiroides Anabaenopsis circularis, A. circularis var. javanica, A. arnoldii, and Microcystis aeruginosa were found in the food bowls as incidental prey. The species D. pulchellum and S. quadricauda could be isolated and cultivated in the laboratory to evaluate their nutritional qualities.