Studies on the biology of reproduction in the cichlid Tilapia nilotica (L.): gonadal maturation and fecundity

Tilapia nilotica reaches maturity in the first year of life; females mature shortly before males (11·4 and 14·3 cm in length). The distinctive morphological features of the different stages of development of the gonads are characterized. The sex ratio varied in populations of different age (size)‐groups: a ratio of 2·81:1 and 0·47:1 (females:males) was obtained in populations of young and old fish. In medium‐sized populations the sexes were equally abundant. There is evidence that females breed more than once a season. Fecundity varied more with body length (r=0·860) and weight (r=0·806) than with age (r=0·604). These variations were of the order of 2·02; 0·83 and 0·83 exponentials of length, weight and age, respectively.