Abstract
The smallscale yellowfish (Labeobarbus polylepis, Cyprinidae), is a large yellowfish species restricted to the southern tributaries of the Limpopo, Incomati and Pongola river systems. This temperate species does not occur below altitudes of 600m and is restricted to perennial rivers with riffles/runs and deep pools. As with most yellowfish species in southern Africa this species is rapidly declining from its known localities. Because of the numerous dams and weirs in rivers, their breeding migrations are often restricted, and the associated flow regimes probably impact on the environmental cues that are a pre-requisite for successful reproduction. Little or no information is available on the breeding ecology of this species. There was thus the need to quantify reproduction requirements of Labeobarbus polylepis assisting aquatic scientists in ensuring flow requirements, conserving spawning habitats and preventing anthropogenic impacts that influence reproduction behaviour and environmental cues. During this study an in-depth investigation was done on the reproductive strategy of Labeobarbus polylepis. This included the habitat requirements, environmental cues associated with spawning, spawning behaviour and the artificial propagation of this species, as well as describing the early life history stages.
From results obtained it is evident that this species spread its reproductive effort over a short period in the early summer season (October). A definite spawning behaviour pattern was observed during this study, which only occurred when environmental cues (daylight length, water temperature and constant low flow) coincides with optimal habitat requirements for spawning. Three definite stages were identified namely pre-spawning behaviour, spawning behaviour and post-spawning behaviour, that is described accordingly. From the observations made during natural spawning, as well as induced spawning, it appears that this previously thought multiple/ serial spawner is in fact a single event spawner. Also, the observed similarity between stream velocity, depth, substrate composition and layout of spawning beds suggest that this species is highly selective in terms of its habitat requirements for breeding. In the developing embryo, the relatively large periviteline space confirm that the eggs are also adapted to fast flowing waters in order to prevent the harmful effects of flow turbulence. Results of this study conclude that Labeobarbus polylepis is a highly specialised breeder that is sensitive to river regulation.
Prof. G.J. Steyn
Prof. F.H. van der Bank