Effet de la variabilité temporelle de la disponibilité de l'aliment sur la croissance d'alevins de tilapia Oreochromis niloticus

Four feeding schedules (three daily ratios given from 08:45 to 13:15 ; 08:45-17:45 ; 13:15-17:45 and 20:30-05:30, GMT+2) were evaluated in juvenile (12 days old) tilapia Oreochromius aureus reared in recirculating aquaria (50 l ; 12 D : 12 N, light at 08:00 ; 27.0-28.5°C ; 325 to 205 fish 50 1^-1). When fed at libitum (d12-42), fish receiving food during daytime had similar growths (ANOVA, Scheffe F-tests, P>0,05) regardless of meal timing (and frequency). The growth of fish fed by night exceeded the mean diurnal growth by 31,1 % (P < 0,05). Similar trends were observed when distributing an optimum food ratio (d43-52 ; conversion rates of 1.16-1.52 and 0.89-0.95, respectively), suggesting that different growth patterns refer to different food conversion effeciencies rather than to different food intakes by day and by night. Applying nocturnal feeding schedules would thus permit to increase the productivity in juvenile tilapia rearing and to smooth daily peaks of organic pollution in fish farm effluents, though the highest growth heterogeneity resulting from nighttime feeding (coeff. var. W_m = 29.3-42.4 % vs 21.0-33.0%) would probably involve more frequent sorting.