Contrary to a recently expressed view very little factual evidence has been brought forward to support the idea that predatory fishes, and especially Lates and Hydrocynus, have had restrictive effects on speciation among other African freshwater fishes. A considerable body of data supports the view that the effects of these fishes do not differ from those of other predators and that predation has facilitated speciation. Further reasons why Lates and Hydrocynus cannot be considered as having effects different from those of other predators are given.
The situation in lakes containing these predators is reconsidered. There is no need to attempt to minimize their effects in Lake Tanganyika where their presence and effects are fully compatible with the existence of a rich endemic fauna. The situation in Lakes Albert and Rudolf is more satisfactorily explained by the brief duration of the existence of the present-day lakes and by their recent invasion by a fully differentiated Nilotic fauna, than by imagining that Lates and Hydrocynus have restricted speciation.
The suggestion that Lates and Hydrocynus were responsible for the inception of the habit of upstream migration for purposes of spawning is discredited, and what seem to be more probable reasons for the phenomenon are given.