The biological characteristics of the Nile tilapia (Oreochromis niloticus) in the Weija Reservoir, Ghana

Abstract

Abstract. Kpelly DK, Blay Jr.J, Yankson K. 2022. The biological characteristics of the Nile tilapia (Oreochromis niloticus) in the Weija Reservoir, Ghana. Intl J Bonorowo Wetlands 12: 41-54. Studies on the biological characteristics of the Nile tilapia (Oreochromis niloticus L.) were undertaken in a manufactured lake, the Weija Reservoir, in Ghana from September 2007 to August 2008. From commercial landings, a sum of 657 specimens of O. niloticus was examined, of which 357 were males and 300 were females (sex ratio of 1: 0.84; P < 0.05). GSI was highest in March and May 2008 and low in December 2007 and August 2008, which suggested that O. niloticus spawned throughout the year, but major spawning occurred in March. The length at first sexual maturity (L50) was 16.33 cm for males and 13.49 cm for females. Observations on the frequency distribution of ovum size measured between 1.2 to 3.1 mm showed two distinct peaks that were not completely separated, which were probably shedding eggs in batches, indicating protracted spawning in the population. Fecundity ranged from 563 to 1542 ova for fish of total length 15.6-21.5 cm with a mean of 851 ± 13.2 eggs. The relationships between fecundity and body weight (BW) and fecundity (F) and total length (TL) were: F = 0.519 BW + 785.4 and F = 12.36 TL + 628.5. Furthermore, based on studies on monthly fluctuations in the GSI and the occurrence of the ripe gonad, the major reproductive activity of O. niloticus in the reservoir coincided with months with increasing total alkalinity, reduced water temperature, and dissolved oxygen. The regression coefficient of 3.1 for the length-weight relationship (for both females and males) was not significantly different from the expected value of (P > 0.05), indicating isometric growth of the population. Therefore, collection of the species as seed for stocking or brood stock or by fish farmers is recommended in March-April. Moreover, appropriate management policies with periodic studies of the fishery and the limnology of the reservoir are essential to sustain fishery production.