Natural foods utilized by Nile tilapia, Oreochromis niloticus, in fertilizer-based fish ponds in Lao PDR identified through stable isotope analysis

Nile tilapia, Oreochromis niloticus, is one of the most popular freshwater aquaculture species in developing countries. Although formulated feed provides higher fish yield, it is expensive. Therefore, fertilizer-based fish culture using natural food sources is generally implemented in developing countries. The aim of this study was to identify the major natural foods contributing to tilapia growth in fertilizer-based fish ponds. The stomach contents of tilapia in a fertilizer-based fish pond in Lao PDR were analyzed to estimate their feeding behaviors; stable isotope ratios of carbon and nitrogen in the potential food organisms and suspended solids were measured and compared with the ratios in the fish muscle tissues. Further, the feed efficiency of chironomid larvae was compared with that of chlorella and formulated feed in a laboratory feeding experiment. Consequently, chironomid larvae were identified as the main contributors to tilapia growth in the fertilizer-based fish pond. In conclusion, benthic larvae of insects belonging to the family Chironomidae are confirmed to be a natural food source for tilapia in the fertilizer-based fish pond.