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 growth 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 two different configurations: rectangular raceways [surface area/volume (SAV) = 4·6:1] and cylindroconical tanks (SAMV) = 2·5:1). Fish were stocked at high densities of 5·6/liter (Expt 1) or 8·4/liter (Expt 2) and fed an androgen-treated diet for sex resersal. 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 versus 2·05–3·02), production (1·65–5·41 versus 1·13–2·34 g/liter) and yield (3·17–4·91 versus 2·24–2·98 fish/liter) than fry reared in cylindroconical tanks. In Expt 2, fry reared in raceways also grew significantly (P < 0·01) faster (0·050 versus 0·039 g/day) than those reared in cylindroconical tanks, with less variation in growth as indicated by coefficients of variation of final weights (69·8 versus 87·1%). Despite equivalent water quality and culture methods, raceways were superior to cylindroconical tanks for production of juvenile Florida red tilapia. The results suggested that raceways, with a high SAV ratio, minimized crowding at the surface during daytime feeding and aggregation on the bottom at night, alleviating aggression and cannibalism and promoting growth.