Lake Tana's piscivorous Barbus (Cyprinidae, Ethopia)

Ecology - Evolution - Exploitation

Stunting is often considered as a major bottleneck for the pond rearing of Nile tilapia (Oreochromis niloticus niloticus L.) and was a major topic in this study. Neonteny: the earlier breeding of tilapia in ponds takes place, but is not a bottleneck as with appropriate feeding levels the somatic growth is maintained.

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The study indicated that aggravation of the living conditions is not a major cause of the observed earlier breeding. Real stunting takes place at low feeding levels but can be avoided by higher feeding levels or by elimination of recruitment through polyculture with either the African catfish (Clarias gariepinus Burchell) and the African snakehead murrel (Parachanna obscura G√ľnther). Recruitment of Nile tilapia is completely controlled at stocking densities of 8300 large catfish ha-1 or 725 large snakehead ha-1.

The difference in predation efficiency between the two species is related to their feeding strategies: omnivorous vs piscivorous. Mass production of fingerlings of the African catfish was carried out in ponds protected against frogs by aluminium roof plates.

The results showed that the developed system is labour orientated, technical reliable and economic feasibly when the fingerlings can be sold for US$ 0.07 a piece. An Individual Based Simulation model for the pond rearing of the Nile tilapia for mixed or mono sex culture, and for poly culture with the African Catfish or African Snakehead is presented.

The model visualized major underlying ecological processes in tilapia farming and indicated that growth and its relation to feed quality, recruitment and prey-predator relations are major topics in tilapia farming modelling. The model can serve as a predictive and decision-making support tool after some slight adaptations discussed.