FEEDING IN DARKNESS ALLEVIATES DENSITY-DEPENDENT GROWTH OF JUVENILE VUNDU CATFISH HETEROBRANCHUS-LONGIFILIS (CLARIIDAE)

Sibling juvenile vundu Heterobranchus longifilis reared at 27 +/- 1 de grees C under 12L:12D were fed during the day, at night or over the en tire 24-h cycle, for periods of 14-15 d. Nighttime feeding gave the hi ghest growth rates, best feed conversion, lowest mortality, fewest los ses due to cannibalism and least growth heterogeneity. The trends were seen in fish of all ages and weights (31-101 d and 0.3-30.0 g), but d ifferences were significant only for the smallest fish that were reare d at the lowest stocking biomass (< 3.5 g.L-1). The effects of daytime and nighttime feeding were examined in 151-d old (85 g) juveniles sto cked at different biomasses (3.4 and 13.6 g.L-1). The growth of vundu was density-dependent, being impaired at low stocking density, but thi s was substantially mitigated under nighttime feeding. Rearing at high stocking density, feeding at night or in darkness, may act through si milar mechanisms that involve changes in the level of aggressive behav iour. It is suggested that nighttime feeding in intensive catfish cult ure could be replaced by 24-h feeding under conditions of permanent da rkness. (C) Ifremer/Elsevier, Paris.