A study on an herbivorous fish,Oreochromis niloticusL., diet and its quality in two Ethiopian Rift Valley lakes, Awasa and Zwai

摘要

The natural food ofOreochromis niloticusfrom two Ethiopian Rift Valley lakes, Awasa and Zwai, was studied from the stomach contents. The food was analyzed to determine its chemical composition. The major consumed nutrient by the Awasa population was carbohydrate whereas in the Zwai population it was lipid. Microscopic identification revealed thatMicrocystissp. andBotryococcus brauniiare the dominant algae present in the food of the fishes from Lakes Zwai and Awasa, respectively. Assimilation efficiency of total organic matter is somewhat low, 28.3 for Awasa and 14.7 for Zwai populations. Both populations assimilated protein to a greater extent than other nutrients. In both lakes the quality of the food, expressed as a ratio of digestible protein to digestible energy, is adequate (>4 mg kJ−1) for growth, but the Awasa population appears to have higher growth and better conditio