Population dynamics of two small cichlid fish species in a tropical man-made lake (Lake Kariba)

Abstract

The population dynamics of two small cichlid fishes (Pharyngochromis darlingi and Pseudocrenilabrus philander) were studied in Lake Kariba, a very large African man-made lake. They are of no economic importance but make up about 14% and 7% respectively of the inshore fish population and are the major components of the diet of fish-eating birds on the lake. P. darlingi isthe larger species (L∞ = 156.5 mm) and is found on both shelving and steep, eroding shores. Its mortality rate differs in each habitat (Z = 0.44 and 0.72 month-1 respectively), only 0.79% survive for 12 months and its {Mathematical expression} ratio is 5.45 (on shelving shores). Ps. philander is smaller (L∞ = 83.9 mm) and is restricted to shelving areas with abundant vegetation. Its monthly mortality rate was high (Z = 7.69), only 0.05% survive to 12 months whilst its {Mathematical expression} ratio was very high (7.69). The estimates of growth obtained for P. darlingi differ considerably from those given in an earlier study in Lake Kariba and some possible reasons for this are discussed. In suitable habitats, the combined production of both species could be 40 kg ha-1 yr-1 which indicates their potential importance to the ecology of the lake. © 1990 Kluwer Academic Publishers.