Ecological notes on the Haplochromis (Pisces: Cichlidae) species‐flock of Lake George, Uganda (East Africa)

Abstract

Lake George, a shallow equatorial lake, supports a Haplochromis species‐flock of 17 species. Of the five species that dominate the species‐flock, two feed mainly on benthic and mid‐water dipteran larvae, one is a piscivore, one exploits microcrustacea and another the abundant blue‐green phytoplankton population. There is little stenophagy in this group. There is a seasonal variation in the total gill‐net catch of the three dominant Haplochromis of the sandy shoal habitat, with high catches in ths wet season and low catches in the dry. Similar fluctuations are known to occur in the commercial catches of Sarotherodon niloticus. No seasonal changes were observed in the proportions of the individual species making up this community and the individuals breed all the year round.A combination of ecologically unspeeialized species, resulting in an efficient exploitation and stability of the ecosystem may account for the observed high fish biomass and the high numbers of individuals. Taking into account the effect of the monotony of the environmental conditions, the physical continuty of the available habitat types and the relatively short time that the lake has been in existence, coupled with the apparent lack of rigid ecological requirements by the individual members of the Haplochromis group, it is suggested that this species‐flock may still be at an early stage in its evolutionary develoment.