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

Abstract

Silver butter catfish (Schilbe intermedius) is an indigenous fish species in Lake Victoria. It has a good economic value because of the quality and freshness of its flesh, increasing its demand for consumption. It is potamodromous, with its stock in the lake declining because of overexploitation by the use of illegal fishing gears at the river mouths on their way to spawning areas. Fish samples (321) were obtained from commercial gill net (1.5–3 in.) fishers within Nyanza gulf. The fish samples were weighed (g) and measured (cm), dissected and sex determined by visual inspection of the gonads. Ovaries for mature female fish specimens were preserved for analysis of fecundity. Fecundity was determined by the gravimetric technique. The mean (±SE) length and weight for all fish were 18.2 ± 0.2 cm TL and 51.9 ± 1.9 g, respectively. The female fish (20.0 ± 0.2 cm) were significantly (F = 199.80, p < .05) larger than the males (15.9 ± 0.1 cm). Similarly, the females (68.8 ± 2.6 g) were significantly (F = 152.61, p < .05) heavier than the males (30.93 ± 1.02 g). The overall sex ratio was 1.23:1.0 (female:male). The length frequency exhibited a unimodal distribution, with the modal class between 16 and 18 cm for either sex. The regression slope (b) of the length–weight relationship was 3.2, 3.1 and 3.0 for all fish, females and males. The absolute fecundity ranged from 6,510 to 59,818 eggs, with a mean of 34,473 eggs. The length at 50% maturity was estimated to be 16.0 cm (female) and 18.0 cm (male) fish. The mean length and size at maturity of S. intermedius have declined, likely attributable to fishing effects, changes in food resources, competition and predation. Thus, the present study provided relevant biological data of S. intermedius, which is currently limited for this region.

Some biological aspects of the Silurid Catfish, Bagrus docmak (Forksskal, 1775) in Lake Victoria, Kenya

“…Furthermore, the results of the present study were not comparable with the findings of Anja et al, (2009) who reported a positive allometric growth for B. docmak (b = 3.24) from Lake Chamo or Keyombe et al, (2015) who also found a positive allometric growth for Clarias gariepinus (b = 3.23) from Lake Naivasha (Kenya). Similarly, the positive allometric growth pattern reported by Mutethya, Okoth, et al, (2020) for S. intermedius (b = 3.30) from Lake Victoria was not in agreement with the findings of the present study. According to Yilmaz et al, (2012) and Ali et al, (2016), fish might show different growth patterns attributable to water quality, food availability, habitat conditions, season and life stages.…”

“…Based on this criterion, B. docmak fish sampled from Lake Victoria during the present study were in a good condition, with a mean K value of 1.0. These results were comparable with the findings of Mutethya, Okoth, et al, (2020) for S. intermedius (K = 1.00), and Yongo and Wairimu (2018) for S. victoriae (K = 1.01) from the Nyanza Gulf of Lake Victoria (Kenya). However, the K results for B. docmak in the present study were not in agreement with the results of Ikongbeh et al, (2012), who reported a K value of 1.62 for the same species from Lake Akata.…”

Length–weight relationship, condition factor, sex ratio and size at first maturity of the blue‐spotted tilapia (Oreochromis leucostictus) in Lake Naivasha, Kenya

“…O. leucostictus exhibited seasonal variations in the condition factor, exhibiting higher values during September and October, and with the lowest values in February of the same year. Considering the seasonality of Lake Naivasha, this observation could be attributed to the availability of more food materials after the long rains in May (Mutethya et al, 2020; Waithaka et al, 2020). The relative condition factor of O. leucostictus in the present study varied with the fish size.…”

“…The lake fishery was closed in 2001 in an attempt to increase fish catches, especially of M. salmoides and C. zillii which were dwindling in numbers. After reopening the fishery in 2002, C. carpio began to appear in catches and has since increased and dominated the lake fishery (Hickley et al, 2015; Mutethya et al, 2020). According to Ojuok et al (2008), C. carpio was accidentally introduced into the lake between 2002 and 2006, with a subsequent change in the fish landing statistics to C. carpio (51%), O. leucostictus (21.9%), M. salmoides (13.2%) and C. zillii (1.5%).…”

A review of the populations of tilapiine species in lakes Victoria and Naivasha, East Africa

“…Negative allometric growth implies the fish becomes more slender as it increase in weight while positive allometric growth implies the fish becomes relatively stouter or deeper-bodied as it increases in length (Riedel et al 2007). The growth and condition factor of fish can be affected by a number of factors such as stress, sex, season, food availability, and other water quality parameters (Mutethya et al 2020). Knowledge of length-weight relationship is important in studying fish biology.…”