Feeding Ecology Of Oreochrohis Esculentus (Pisces:Cichlidae) In Lake Kanyaboli, Kenya

Abstract

The food and feeding habits of Oreochromis escuientus in Lake Kanyaboli were investigated from September 1989 to August 1990 during which a total of 1305 fish stomachs were examined. The diet consisted of a broad spectrum of food types, including phytoplankton, zooplankton and detrital material. The blue-green algae (Cyanophyta) and green algae (Chlorophyta) were the principal food types, constituting about 701. and 241. respectively by numbers, of the foods consumed . Diatoms (Bacillariophyta), euglenoids (Euglenophyta) and zooplankton were also consistently present in the diet of this species. O. escuientus of different sizes in Lake Kanyaboli fed on similar food types. The diet composition remained the same throughout th~ year as did the composition of phytoplankton in the water. Diatom and zooplankton components of the diet were digested while most blue-green and green algae as well as euglenoids passed out through the gut undigested. O. escuientus tended to select the Bacillariophyta and zooplankton, which are digestible, and, to some extent, the euglenoids. This species, however, rejected blue-green and green algae, which it was not capable of breaking down. O. escuientu5 in Lake Kanyaboli fed during the day, and digested and assimilated food at night. It fed actively from 0700h until 1700h, when peak feeding activity occured. Thereafter, digestion progressed steadily until stomachs. The presence of a lower pharyngeal bone armed with 0600h when 901. of the fish progressed had empty activity occurred. Thereafter, digestion slender teeth hooked at the distal end, an upper pharyngeal bone with teeth cusped at the distal end, a poorly developed i.e. less mascularized sac-like stomach and an intestine of considerable length (standard length to intestine length ranged from 1:4 to 1:14), all attest to the phytoplanktivorous diet of O. esculentus. Both male and female O. esculentus exhibited isometric growth. The overall length-weight relationship was given by: Log W = -4.523 + 3.022 Log L. There was no significant difference in the condition of fish of different sizes or sexes, or at different times