Life history traits of Bathyclarias nyasensis (Siluroidei) in Lake Malawi
Life history traits, including age, growth, reproduction and diet of Bathyclarias nyasensis from Lake Malawi were studied between December 1996 and November 1998. Owing to reabsorp tion of pectoral spines with increasing fish size, and the relatively low number of spines that could be aged reliably, only otoliths were used to age fish. The maximum age for B. nyasensis was estimated at 14 years. There was no difference in growth rate between males and females. Age at 50 % maturity for females and males was estimated at seven and four years, respec tively. The age of fish was validated using marginal zone analysis. The results need further validation, however, owing to the high percentage of samples having opaque marginal zones in all months, the failure to explain the occurrence of peak marginal zones in particular months and the high percentage of otoliths that were rejected. The hypothesis of rapid fish growth in the first year and slow growth during subsequent years was supported by results from stomach content analysis. Smaller fish that were found inshore were predominantly piscivorous while larger fish that were found in offshore regions were mostly zooplanktivorous. The utilization of zooplankton in offshore areas suggests that B. nyasensis relies on the pelagic food web in Lake Malawi.
Key words: African lake fish, ageing, stomach content analysis, pelagic food web.