Reproductive biology and condition factor of the catfish Bagrus docmak (Forsskål) (Pisces: Bagridae) in Lake Chamo, Ethiopia

Abstract

Some aspects of reproductive biology, length-weight relationship and condition factor of 534 (258 males and 276 females) Bagrus docmak (Forsskål) in Lake Chamo were studied from samples taken during February 1995 to February 1996. B. docmak had an extended breeding period from February to August, with peak spawning in May for both sexes, when 76.2% males and 78.3% females had ripe gonads. The main pulse in breeding activity occurred during the rainy months of April and May. The overall sex ratio (male: female) was 1:1.07 which did not deviate significantly from the hypothetical distribution of 1:1 (x² =0.61, p>0.05). However, sex ratio was significantly different from 1:1 in the samples >90 cm fork length (FL) (x² = 10.71, p< 0.001). Size (FL) of first maturity was 62.0 cm for males and 69.0 cm for females. The mean number of eggs per female was 276,500. Ripe ovaries contained 990–2,100 eggs per gram of preserved wet weight with a mean number of 1,475. Fecundity was positively related to FL (r² = 0.75, p< 0.05), total weight (TW) (r² = 0.73, p< 0.05) and ovary weight (OW) (r² = 0.90, p< 0.05). Length-weight relationship of B. docmak is best expressed by the equation TW= 0.0054FL^3.24. Monthly Clark’s condition factor (mean +/- SE) ranged from 0.426± 0.011 to 0.489± 0.014 for males and from 0.449± 0.010 to 0.489± 0.012 for females.