FOOD AND FEEDING HABITS OF NILE TILAPIA, OREOCHROMIS NILOTICUS (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.