Spawning behaviour and early development of the Clanwilliam yellowfish (Barbus capensis; Cyprinidae), linked to experimental dam releases in the Olifants River, South Africa

This paper describes an investigation of how experimental releases of pulses of high flow from Clanwilliam Dam (Olifants River, South Africa) affect spawning of the Clanwilliam yellowfish, Barbus capensis. This species is endemic to the Olifants River system and is listed as rare in the Red Data Book of fishes for South Africa. Spawning sites are described, as is the spawning behaviour of B. capensis after specific experimental pulses released during the suspected spawning season of the species. Spawning and the developmental stages of embryos, free embryos, and larval B. capensis were studied using direct observations, video recordings, and microscopic examination of live embryos. B. capensis was found to be a repeat‐spawner over several days as well as a multiple‐spawner throughout the 4 month reproductive season. At present, spawning of B. capensis occurs down‐stream of the dam sporadically (and possibly with limited recruitment), concurrent with releases of water for irrigation purposes. Experimental pulses appeared to trigger an increase in spawning activity, as an abundance of larvae was found down‐stream 2 months later. It is suggested that a water‐release strategy from Clanwilliam Dam could be designed to increase the number of B. capensis in the Olifants River. © 1997 John Wiley & Sons, Ltd.