Feeding habits, ontogenetic dietary shift and some aspects of reproduction of the tigerfish hydrocynus forskahlii (Cuvier, 1819) (Pisces: Characidae) in Lake Chamo, Ethiopia

Abstract

The diet composition, ontogenetic dietary shifts and reproduction of the tigerfish Hydrocynus forskahlii (Cuvier, 1819) were studied from 386 fish samples (11.2 cm-69.6 cm total length, TL) collected from Lake Chamo from January to August 2005. From the total number of fish samples 231 (59.8%) that contained food in their stomachs were used in the analysis. Zooplankton occurred in 35.8% of the stomachs examined, accounted for 78.8% numerically and constituted 10.3% volumetrically. Insects occurred in 58.5% of the stomachs examined, constituted 20.8% of the total number of prey organisms and accounted for 38.7% of the total volume of the food items. Tilapia fry occurred in 43.4% of the stomachs examined, constituted 0.73% of the total number and 50.3% of the total volume of the prey. Macrophytes occurred in 18.9% of the stomachs and accounted for 0.74% of the total volume. H. forskahlii fed mainly on zooplankton when young and shifted to piscivorous feeding habit when it attained the size of about 25 cm TL. The sex ratio was significantly different from unity where 306 (79.3%) females and 80 (20.7%) males were caught during the sampling period. Relative fecundity of H. forskahlii ranged between 135 and 204, while mean fecundity ranged between 35,564 and 411,810. The relationships between fecundity (F) and TL (F = 0.0184TL4.08, r² = 0.61) and F and total weight (TW) (F = 36.89TW1.23, r² = 0.70) were curvilinear while the relationship between F and ovary weight (OW) (F = 4082.9OW 7949.5, r² = 0.88) was linear.

Keywords/phrases: Diet composition, H. forskahlii, Lake Chamo, Reproduction

Ethiop. J. Biol. Sci., 7(2): 123-137, 2008