Aspects of Growth, Diet, and Reproduction of <i>Oreochromis niloticus</i> (Linnaeus, 1758) in a Hypertrophic Milieu, the Municipal Lake of Yaoundé, Cameroon

Abstract

The Nile tilapia, <i>Oreochromis niloticus</i>, is a highly valued fish species in Africa for subsistence and commercial purposes. However, overfishing activities in non-supervised lakes or reservoirs threaten its availability. In the view of contributing to the database on the life history traits of this species in Cameroon and supporting its sustainable management, the present study investigated the growth patterns, food preferences, and reproductive aspects of <i>O. niloticus</i> in a hypertrophic milieu, the Yaoundé Municipal Lake, from May to October 2018. Fish specimens were sampled, measured, weighed, and sexed. The digestive tract of each specimen and the females’ gonads were collected. The intestines were measured, and the stomach contents were identified. The females’ reproductive aspects were determined. Overall, 101 specimens were collected and distributed among 48 (47.5%) males and 53 (52.5%) females, with a sex ratio of 1: 1.1. In this hypoxic (1.35 ± 0.4 mg/L) and highly conductive (210.5 ± 56.9 µS/cm) milieu, <i>O. niloticus</i> displayed a relatively good condition (<i>Kn</i> > 1) throughout the sampling period and negative allometric growth patterns for both sexes (<i>b </i>< 3; <i>p</i> < 0.001). Materials from plant origin were the preferred prey types, with an index of relative importance (IRI) of 78.20%; meanwhile, mud and materials from animal origin were secondary prey items (IRI: 13 ‒ 17%). The relative gut length (RGL) value above 3.0 and the foraging activity on detritus suggest that <i>O. niloticus</i> has an herbivorous or detritivorous dietary habit and is a bottom-feeder. Female length at first maturity (L<sub>50</sub>) was 17 cm. Their gonado-somatic index (GSI) showed sexual activity throughout the whole sampling period, with the peak spawning phase happening in August. The absolute fecundity of gravid females varied between 316 and 1816 oocytes (942 ± 430 oocytes), and the relative fecundity ranged from 1–5 oocytes/gram of body weight (3 ±1 oocytes/g). The results highlight the performance of the Nile tilapia in this ecosystem and provide information for its sustainable use and improvement of fish culture.