Reproductive activities of two zooplanktivorous clupeid fish in relation to the seasonal abundance of copepod prey in the northern end of Lake Tanganyika

Reproductive activities of two commercially exploited clupeid fishes (Stolothrissa tanganicae and Limnothrissa miodon) in the northern end of Lake Tanganyika (Bujumbura sub-basin) were investigated during two different years (2004-2005 and 2007-2008). We hypothesized that the timing of largest reproductive investment in these pelagic species coincides with the onset of the rainy season and the highest abundance of copepod prey. For S. tanganicae, the gonadosomatic index (GSI) was significantly higher prior to the onset of the rainy season, and this was observed in both years. For L. miodon, however, this pattern was overall weaker and only statistically significant in 2004-2005. In both species, spawning activities did not seem to be adjusted to provide optimal feeding conditions for the larvae. Instead, investment in reproduction seemed to be related to the availability of copepods in the preceding months. We conclude that the timing of reproductive activities in these clupeids is species-specific, and might be subject to strong year-to-year variation.