Some aspects of reproductive biology of the Crucian carp Carassius carassius (L., 1758) (Pisces: Cyprinidae) in Lake Ziway, Ethiopia

Abstract

Some aspects of reproductive biology of Carassius carassius (L.) such as sex ratio, breeding season, size at first maturity and fecundity were studied from 539 fish samples collected from October 2003 to September 2004 in Lake Ziway, Ethiopia. The overall sex ratio (male: female) was 1.1.7 and deviated significantly from the hypothetical distribution of 1:1 (x² =35.9, p< 0.001). Sex ratio was significantly different in all size classes >35.0 cm total length (TL) in November and December 2003 and in January, March and April 2004. The size at first maturity (L_m50) of males was 26.8 cm TL while L_m50 of females was 30.5 cm TL. C. carassius had an extended breeding period from December to June, with peak spawning in February for both sexes when 75.0% males and 71.4% females had ripe gonads. The main pulse in breeding activity occurred during the early rains. The total number of eggs in the ovaries ranged between 81,674-10,616 with the mean number of 194,900 eggs female^-1. Ripe ovaries contained 748-1,442 eggs g^-1 of preserved wet weight with a mean number of 981. Fecundity was positively related to TL (R² = 0.66, p<0.05) and total weight (TW) (R² = 0.71, p<0.05). C. carassius conformed to the general pattern of reproduction in a tropical environment where breeding activity started during the early rains. In order to protect the spawning population, fishing pressure should be minimized during breeding time at shallow littoral regions.

Keywords/phrases: Breeding season, Commercial fishery, Fecundity, Introduced species, Size at first maturity

Ethiop. J. Biol. Sci., 8(2): 109-121, 2009