Food and feeding habits of Nile Tilapia, <i>Oreochromis niloticus</i> (L.) (Pisces: Cichlidae), in Lake Langeno, Ethiopia

Abstract

The study aimed to determine the diet composition, dietary change and diel feeding pattern of Oreochromis niloticus, in Lake Langeno. Fish specimens were collected monthly from July 2017 to June 2018 using a beach seine with 40 mm mesh size and scoop-net with small mesh size (1.0 mm). A total of 264 non-empty fish stomachs were examined for dietary analysis. The relative importance of different food items was analyzed using frequency of occurrence (%FO) and numerical abundance (%N). The most frequently encountered food items in the stomach of O. niloticus were phytoplankton, zooplankton, macrophytes and detritus. Among the phytoplankton groups, the genera Microcysts (%FO = 85.25), Cyclotella (65.51), Anabaena (%FO = 50.0), Cymbella (%FO = 65.15), and Chlorella (%FO = 54.17) contributed the most. Numerically, Cyanophyta, Chlorophyta, Bacillariophyta, and Zooplankton contributed 5.2%, 3.4%, 53.03% and 42.28%, respectively, to the total food items. Insect and fish remains occurred in rare occasions in the stomach content of all length groups of fishes. The dominance of animal-based food items progressively decreased as the fish grew to larger size while the importance of macrophytes and detritus increased. O. niloticus feeds mainly during the day time and stomach fullness peaked at 16:00 hr. The daily food consumption rate and gastric evacuation rate were 9.0% body weight and 48% per hr, respectively. Crude protein dominated nutrient composition of the fish and this could be attributed to the high  percentage in frequency of nutritious diets like Rotifers (64.0%), Cladoceras (63.6%) and Microcystis (85.6%). It can be concluded that juvenile Oreochromis niloticus feeds mainly on animal food sources whereas adults feed primarily on macrophyte food items.