Weaning success of southern flounder juveniles: Effect of changeover period and diet type on growth and survival

Two studies were conducted to determine the effects of changeover period du ration and diet type (dry versus semimoist) on growth and survival of postm etamorphic southern flounder Paralichthys lethostigma during weaning from l ive feed onto formulated feeds. In the first study, feeding with live brine shrimp Artemia sp. was abruptly stopped after changeover periods of 5, 10, 15, and 20 d. A changeover period of 20 d resulted in significantly higher (P < 0.05) survival (mean +/- SE: 65.2 +/- 2.5%) than for the 5, 10, and 1 5-d treatments (28.8 +/- 15.5%, 30 +/- 11.2%, and 40.0 +/- 12.4%, respectiv ely). Overall growth was not significantly different (P > 0.05) from the ot her treatments or the control (live brine shrimp). In the second study, fee ding with live brine shrimp was gradually reduced from 100% to 0% over a 12 -d changeover period. Brine shrimp were replaced with either a dry feed or a semimoist feed. Survival of fish fed either the dry feed (71.1 +/- 30.1%) or the semimoist feed (71.1 +/- 15.4%) was not significantly different fro m fish in the control treatment (93.3 +/- 6.7%). Optimum growth and surviva l of postmetamorphic southern flounder during weaning requires a changeover period of 20 d when the use of live feed is abruptly ceased, but this peri od can be shortened when gradual weaning is employed and when diets with gr eater acceptability are used.