Length-weight relationship, condition factor and feeding habit of the Silurid Catfish Bagrus docmak (Forksskal, 1775) in Lake Victoria, Kenya

Abstract

Bagrus docmak is a species of the Bagrid catfishes that is indigenous to Lake Victoria, and is an important source of livelihood to communities around the lake. Fish samples were caught using gillnets of mesh sizes 50 mm and 10 mm. The length and weight of individual fish was measured in the field, while stomachs were preserved in 5% formalin and taken to the laboratory for gut content analysis. The overall sex ratio (male: female) was 1.0:1.26 which did not deviate significantly from 1:1 (p > 0.05). The length of fish ranged from 12.0-55.0 cm TL and weighed between 20.0 g and 1650.0 g, with mean length and weight of 32.7 cm TL and 351.2 g, respectively. The relative condition factor was 0.97, 1.01 and 1.00 for male, female and combined sexes, respectively. The condition factor was not significantly different in relation to sex of fish and size classes (p > .05). The slope b of the length-weight relationship was 2.94, 2.94 and 2.90 for females, males and combined sexes, respectively. Analysis of stomach fullness revealed that most of the stomachs were ¼ full (44.6%), while (29.7%) were empty. Non-empty guts had variety of food items with Caridina, insects and fish remains each contributing the highest (21%) proportions. Most stomachs in each size class were ¼ full, and empty stomachs notably reduced with increased fish size. Juveniles of less than 30 cm TL fed exclusively on Caridina; otherwise with increased size the fish ingested insects, and different fish species such as Barbus, bivalve, Haps, crabs and detritus in variable quantities. This study provides information on the length weight relationship and condition factor of B. docmak useful for its management. Knowledge of its food requirements in the wild can be used to inform feed formulation for its successful culture.