The use of natural food by Oreochromis niloticus raised in earth ponds with ration

Abstract

Informations about natural feeding of Nile tilapia, Oreochromis niloticus, raised in semi-intensive farming system in earthen ponds, may contribute to improve the management in order to decrease production costs. Hypothesis: a) O. niloticus ingest considerable amount of natural food even when raised with ration; b) There are preferential feeding schedules for ingestion; c) There are preferential food items among the natural ones. Hypothesis test: The quantitative evaluation of food items from the gut content of 208 animals was carried out using numeric, displacement-volumetric and gravimetric methods. Data were obtained from two 24 hours samplings realized in November 1997 and March 1998 at Pond 1 at each 4 hours, the first one in order to determine a schedule representative of ingestion and to evaluate the feeding chronology. From November to March, four biweekly samplings were done in Ponds 1 and 2, to complete the quantitative evaluation of endogenous natural food items ingestion. The following indices were applied: repletion, electivity and preponderance. Results show that there are preferential schedules of natural food ingestion and that the amount ingested was considerable. The diet consisted of ration, detritus, vascular plants, algae, and micro and macroinvertebrates, indicating that the tilapia behaved as omnivorous species, with preference for microalgae and Chironomidae larvae. The hypothesis validation indicates that management can be improved through a better use of the natural food, in order to decrease environmental and financial production costs.