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 is the larger species (Lo = 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-' respectively), only 0.79% survive for 12 months and its P/B 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 P/B 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-' yr-1 which indicates their potential importance to the ecology of the lake.

Trophic interrelationships amongst cichlid fishes in a tropical African reservoir (Lake Chivero, Zimbabwe)

“…Interspecific competition might also explain the success of T. sparrmanii, almost unknown in the lake 20 years ago (Marshall, 1982) but now apparently more numerous than T. rendalli. The other species that might compete with each other are the two small omnivores, P. acuticeps and P. philander, but their unspecialised diet may reduce competition, as would their rather different habitat preferences with philander being more numerous in vegetated areas while acuticeps occurs amongst rocks or in areas without plants (Hustler & Marshall, 1990).…”

Effects of habitat and fishing on fish assemblages in a tropical reservoir: Lake Kariba, Zimbabwe

“…The significant differences in mean lengths for some species (e.g. P. philander), for example, might have been largely due to skewed length distribution that might actually reflect a seasonal difference in the species population inshore areas, as observed by Hustler and Marshall (1990).…”

“…Other previous studies have revealed differences in fish communities in relation to habitat. An example is the study of Marshall and Langerman (1988) who, using explosives, found fish biomass was much higher among vegetation, while Hustler and Marshall (1990), using traps, determined habitat preferences for two small cichlids.…”