The objectives of the study were to assess the reproductive biology of Oreochromis niloticus and point out implications for fisheries management. Relevant biological data (total length (TL), total weight (TW), sex ratio, maturity stages and fecundity were collected. The collected data were summarized using descriptive (percentage, graphs, tables) and inferential (Chi-Square, Regression) statistics through the application of SPSS. The data were compared with the past reports in the area. A total of 738 samples (422 females and 316 males) were collected during the sampling period. There was a significant deviation in sex ratio (Females: Males), (1.3:0.75) from the hypothetical 1:1 ratio (Chi-Square, P<0.05). The fecundity of Nile tilapia ranged from 190 to 616 eggs with a mean of 328 eggs. A strong positive relationship between fecundity and body sizes (fish length and body weight) with r2 > 0.95 was observed in Lake Hayq. The smallest sexually mature fish specimen caught in the current study was 9.3 cm TL and 14 g TW. The size at first sexual maturity (L50) was 11.5 cm for both females and males, which is unexpectedly low. In this study, the main breeding season for O. niloticus was from February to April with peak breeding season in April. Heavy fishing, illegal fishing activities, fishing during the breeding season and breeding ground, and destruction of breeding and feeding grounds are the major problems of Lake Hayq.
Keywords: Fecundity, Fishing stress, Lake Hayq, Length at first maturity, Nile tilapia, Sex ratio