Fishing methods, catches, fish species diversity, water quality and diets were examined in the middle Nyong River basin of south-central Cameroon over five years. Out of 79 indigenous species from the upper and middle Nyong in museum collections, 17 indigenous species added in this study (total = 100) and two feral alien species, only 38 are regularly captured by commercial fishers, and only 18 of these are sufficiently abundant and large enough to be of importance as food fish. Two of the most important are the alien Oreochromis niloticus and Heterotis niloticus. Although quantitative data are lacking on the state of the ecosystem at the time of earlier fish collections, there is circumstantial evidence that indigenous species may have suffered from competition with introduced aliens and/or changes in the ecosystem resulting from poor land use management and the use of pesticides in fishing.