Introduction
Genetically improved farmed tilapia (GIFT) of the species Oreochromis niloticus is a popular food fish all over the world. In India, this species got in-to aquaculture a decade back and registered steady growth in terms of production. However, a foolproof technology for high density culture was lacking. In this context, comparatively less expensive high-density GIFT culture under RAS mode has been developed and transferred to field successfully.
Methods
The technology has three major components, Pond designed to have 6.7m length 6.7m width x 2m depth to accommodate 90m3 water, and the bottom made conical with 18° slope and a central pit of 30cm diameter and 30cm height to facilitate easy and steady accumulation of detritus (slurry) removable with slurry pump and diverted for vegetable cultivation, Mechanism of circulation of water combined with heavy aeration through air injectors operated with a 0.5hp centrifugal pump creating swirling motion and concentration of the slurry at the central pit and nitrification and denitrification established by installing specially designed three activated trickling filters using nitrifying bacterial consortium having in-it denitrifying bacterial components as well. The system is exposed to sunlight to facilitate micro-algal growth generating much of the oxygen needed during day time. Fishes are stocked in three cages having 30m3 water columns and each to hold a minimum of 1500 fishes.
Results
Within a period of four months fishes registered growth from 5 to 400 grams having FCR 0.98 suggesting that they eat on microalgae in the form of periphyton attached to the cage nets. During the culture period consistent water chemistry could be maintained.
Discussion
The system which facilitates regular stocking and continuous harvest and sale can be operated by homemakers, and a mini integrated water testing laboratory facilitates regular monitoring of water chemistry with adequate corrections using dolomite. This system has been adopted by National Fisheries Development Board, Ministry of Agriculture and farmers Welfare Hyderabad named as "Backyard RAS" for nationwide dissemination.