Maturation, sex ratio and fecundity of the Nile perch <I>Lates niloticus</I> (L.) (Pisces: Centropomidae) in Lake Chamo, Ethiopia

Abstract

Length-weight relationship, length at first maturity and sex ratio of the Nile perch Lates niloticus (L.) were studied from 342 fish samples collected between February 1995 and May 1996. The relationship between total length (TL ) and total weight (TW) for both sexes was curvilinear and statistically significant. The regression equation for the males was TW=0.0044TL 3.27 (r2=0.978, P<0.001) and that for the females was TW=0.0058TL 3.2 (r 2 =0.991, P<0.001). 50% maturity size of males and females were found to be 88 cm and 106 cm TL respectively. The overall male to female sex ratio of 1: 0.64 was significantly different from the theoretical 1:1 ratio (χ2=16.0, P<0.001). Generally males were more numerous at smaller size classes while females predominate at larger size classes. Forty-nine fish samples that ranged in length from 106.8 cm to 192 cm TL and in weight from 17,000 g to 108,000 g TW were used in fecundity estimates. The weight of ripe ovaries ranged from 325 g to 5,600 g with the mean weight of 934 g. Fecundity ranged between 1.24 million and 37.44 million eggs. The total and relative mean fecundity of L. niloticus was 6.35 million eggs female -1 and 162 eggs g -1 TW. The average number of eggs g -1 of ovary ranged from 6,200 to 9 ,300 with the mean number of 8 ,100. The relationships between fecundity and TL (F=0.0034TL 4.32, n=49, P<0.01) and fecundity and TW (F=0.4357TW1.55, n=49, P<0.01) were curvilinear while the relationship between fecundity and ovary weight (OW) (F=8,017OW-84,461, n=49, P<0.01) was linear.