Life History Of Chrysichthys Catfish In Volta Lake,Ghana.

Abstract

This study, undertaken during 1974 to 1977 in Volta Lake, investigated the identification, abundance and distribution, reproductive biology and weight-length relationships of four Chrysichthys species (C . a u ratus, C. walkeri, C. velifer and C. furcatus). The species were separated on basis of position of the dorsal fin, color of the barbels and the body and shape of the caudal fin and its lobes. Gill rakers also proved of some value. The Volta Lake, on the Volta River in Ghana, is the largest manmade lake (area: 8,700 km^). It was dammed in 1964 and reached the m a x i mum controllable level in 1968. The northern narrower arms are of riverine character and the southern section, lacustrine. Water temperatures range between 26.5 to 30.5°C throughout the year. Except in periods of overturn (usually between December to March and June to August), dissolved oxygen is considerably reduced below 10 m. Ampem station, established on one of the main arms of the lake, was sampled monthly (except 9 out of 29 months) with gill nets of graded mesh size, a beach seine, traps (hoop nets) and rotenone. Other stations, in the various sections of the lake, were also sampled occasionally. ln 196 5 Chrysichthys were relatively abundant near the dam at Akosombo. Sampling in 1970 showed a decline and a more even lakewide Life history of Chrysichthys catfish in Volta Lake, Ghana University of Ghana http://ugspace.ug.edu.gh distribution with indications of higher abundance in the southern (more lacustrine) areas. Thereafter, abundance fluctuated seasonally with more fish being caught in the rainy season. Chrysichthys were seldom found deeper than 10 m, probably because of low dissolved oxygen concentrations. Chrysichthys also were seldom found in higher currents. Length frequency data did not indicate different year classes or spawning periods but were characterized by single modes which remained fairly constant over a 6 -month period. Spawning C. walkeri and C. auratus were taken in traps fabricated from bamboo stems. Spawning was in a sheltered bay at depths of 1.0-1.5 m over a firm substrate and egg masses were placed in darkened interior of the bamboo traps. The smallest (standard lengths) spawning males, and females were respectively 76 m m and 82 mm (C. auratus) and 82 m m and 72 m m (C. walkeri). Males were larger than their mates in 42 of the 43 pairs collected in the bamboo traps. The number of eggs per female increased linearly with weight for C. walkeri and with weight and length for C. velifer and linearly with the log lengths of C. walkeri and C. auratus. The slopes for functional regressions of log weight on log length did not differ significantly from 3.0 for C. walkeri and C. velifer but was less than 3.0 for C. auratus and C. furcatus.