Hatchery production of Florida red tilapia seed in brackishwater tanks under natural-mouthbrooding and clutch-removal methods

Abstract

Hatchery production of Florida red tilapia seed (eggs, sacfry and fry) in brackishwater (12 ppt) tanks was studied on Lee Stocking Island (Exuma Cays, Bahamas) under two methods of broodstock management. Six above-ground tanks (34.2 m 2) were each stocked with 240 year-class 1 breeders (avg. wt. = 143 g) at a ratio of 3 females to 1 male. Seed production was monitored either under the natural-mouthbrooding method by collecting free-swimming (i.e., post-yolksac stage) fry from tanks every 8–16 days, or under the clutch-removal method by removing free-swimming fry from tanks, and eggs and sacfry from the mouths of brooding females every 15–16 days, and assessing the numbers of each. Seed production over a 3-month period under the natural-mouthbrooding method (3.3 seed m −2 day −1) was significantly lower ( P < 0.001) than that obtained under the clutch-removal method (91.7 seed m −2 day −1) which is among the highest reported for tilapia hatcheries. Poor seed production under the natural-mouthbrooding method was attributable to cannibalism of eggs and fry by adults. Hatching success of eggs in upwelling incubators averaged 64.8% with effects of densities of 462, 923, 1385 and 1846/1 not differing significantly ( P > 0.05). Fry obtained from artificial incubation were significantly ( P < 0.05) larger (9.9 mg vs. 7.5 mg) and more viable than those obtained through natural mouthbrooding as evidenced by higher survival (73.9% vs. 49.7%) during a 29-day sex-reversal period. The results suggest that the clutch-removal method, while more labor intensive, yields markedly higher numbers of viable fry for growout.