Examinations of the stomach contents of two fish species (Clarias gariepinus and Oreochromis niloticus) in Lake Alau, North - Eastern Nigeria

摘要

This study was conducted on the examinations of the stomach contents of two commercially important fish species of Catfish and Tilapia fish (Clarias gariepinus and Oreochromis niloticus) known as "Tarwada" and "Karfasa" in Hausa language, determined from Lake Alau, North - Eastern Nigeria, using frequency of occurrence and volumetric methods between June to December, 2013. Gill nets and Malian traps were used to catch the fish every fortnight. Three hundred and fifty (350) individual fish of each species obtained and their stomach contents examined. The results obtained expressed in mean percentage indicated that out of the three hundred and fifty (350) individual fish of each species examined, 121 (35%) fish had an empty stomach contents in Clarias gariepinus, and out of the 350 samples examined, 145 fish had an empty stomach content in Oreochromis niloticus representing 41%. The stomach contents of Clarias gariepinus consisted of animal and plant materials, planktons, (zooplanktons and phytoplankton) and others. Fish prey was the dominant animal material (51%) with mean contribution of 32% by volume, and plant material consisted of leaves and offal (6% by volume). The stomach content of Oreochromis niloticus consisted mainly of animal and plant materials, planktons and detritus. Algae represented by Chlorella, Volvox, Scenedesmus, Pediastrum, and Spirogyra species accounted for 66% by volume followed by detritus and mud with 20 %, zooplankton represented by Daphnia and Moina species represented the low food content by volume with 8 %. The study reveals the importance of algae, fish, insects and plant materials as food for fish in Lake Alau, and zooplanktons form important items in the diet of the species examined. Both species are omnivorous and occupy the same ecological niche; hence, there is the need to control pollution into the lake to prevent eutrophication.