Some aspects of the biology of Nile perch, Lates niloticus, in the open waters of Lake Victoria, Kenya

Abstract

Samples (6404) of Nile perch were collected monthly from commercial catches between June 2014 and June 2015. The total length (cm), weight (g) and sex of fish were all determined in the field, with 3771 (59%) being male and 2059 (32%) being female fish, for an overall sex ratio of 1.83:1.00 (male: female). The average length and weight for all fish were 55.38 ± 0.14 cm TL and 2355.10 ± 22.30 g, respectively. The size of male fish ranged from 15.5 to 128.5 cm TL and weighed between 190 and 25 000 g, whereas that of female ranged from 21.0 to 130.0 cm TL and weighed between 124 and 25 800 g. The value of the regression slope b of the length–weight relationship was equal to 3.04. The mean (±SD) condition factor for all fish was 1.23 ± 0.13. The condition factor was different in the length groups, with the highest (1.32 ± 0.13) and lowest (1.12 ± 0.20) values recorded in length groups 100–110 and <30 cm TL, respectively. The highest and lowest condition factors were recorded between January and March, respectively. The length–weight relationship and condition of Nile perch in Lake Victoria have deteriorated greatly, this finding being linked to the reduction of its prey species in the lake.

Biological aspects of Schilbe intermedius (Ruppell, 1832) in the Nyanza Gulf of Lake Victoria, Kenya

“…The variations in b between study sites may be attributable to differences in the environmental conditions. The b value can be used as an indicator of food intake and may differ according to biotic and abiotic factors, food availability and habitat type (Yongo et al, ). Length–weight relationships for fish have been used extensively to provide information on the condition of fish and their isometric or allometric growth (Yongo, Outa, Kito, & Matsushita, ).…”

“…The most important commercial fish species in Lake Victoria until the 1960s were Schilbe intermedius , Protopterus aethiopicus , Claria s gariepinus, Bagrus docmak, Momyrids, Labeo victorionus, and the tilapiine species Oreochromis esculentu s and O. variabilis (Ogutu‐Ohwayo, ). When Lates niloticus , O. niloticus, O. leucostictus, Tilapia zillii and T. rendalii were introduced, the lake ecological system changed because of predation and competition for food (Yongo, Outa, Kito, & Matsushita, ). In the early 1990s, B. docmak , C. gariepinus and S. intermedius were the top predators in Lake Victoria (Corbet, ).…”

Growth, mortality and recruitment of Nile perch (Lates niloticus) in Lake Victoria, Kenya

“…() reported that fish below and above the slot size has continued being caught and processed, thereby confirming the slot size is hardly adhered to by both the fishers and the processors . Reductions in the sizes of L. niloticus are likely attributed to the illegal gears and methods used in the fishery (Yongo et al, ). Fishers in Lake Victoria have increasingly abandoned large‐meshed gillnets in favour of small hooks on long lines (Mkumbo & Marshall, ), which largely targets small size Nile perch.…”

Changes in some biological parameters of the silver cyprinid, Rastrineobola argentea (Pellegrin, 1904) in the Nyanza Gulf of Lake Victoria, Kenya

“…The increased condition of female and decreased conditions for males with increasing size, however, could be attributable to gonadal development and spawning conditions. In fact, the condition of fish is affected by changes in food availability, environmental quality, season and reproduction status, among other factors (Yongo, Outa, Kito, & Matsushita, ). Previous studies on the fecundity of R. argentea are summarized in Table .…”