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 reabsorption 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, respectively. 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.