COMPARISON OF RACEWAY AND CYLINDROCONICAL TANKS FOR BRACKISH-WATER PRODUCTION OF JUVENILE FLORIDA RED TILAPIA UNDER HIGH STOCKING DENSITIES

Under commercial-scale hatchery conditions, survival, growth and growt h variation were compared for post-yolk-sac stage Florida red tilapia reared for 21 days in 350-liter brackish-water (12-14 ppt) tanks of tw o different configurations: rectangular raceways [surface area/volume (SA/V) = 4.6:1] and cylindroconical tanks (SA/V = 2.5:1). Fish were st ocked at high densities of 5.6/liter (Expt 1) or 8.4/liter (Expt 2) an d fed an androgen-treated diet for sex reversal. In both experiments, fry reared in raceways showed significantly (P < 0.01) better survival (59.6-61.3 versus 34.6-42.2%), feed conversion ratios (1.04-1.97 vers us 2.05-3.02), production (1.65-5.41 versus 1.13-2.34 g/liter) and yie ld (3.17-4.91 versus 2.24-2.98 fish/liter) than fry reared in cylindro conical tanks. In Expt 2, fry reared in raceways also grew significant ly (P < 0.01) faster (0.050 versus 0.039 g/day) than those reared in c ylindroconical tanks, with less variation in growth as indicated by co efficients of variation of final weights (69.8 versus 87.1%). Despite equivalent water quality and culture methods, raceways were superior t o cylindroconical tanks for production of juvenile Florida red tilapia . The results suggested that raceways, with a high SA/V ratio, minimiz ed crowding at the surface during daytime feeding and aggregation on t he bottom at night, alleviating aggression and cannibalism and promoti ng growth.