Effect of feeding time on dietary protein utilization and growth of juvenile Senegalese sole (Solea senegalensis)

The present study aimed to determine the effect of feeding time on growth and nitrogen excretion in juvenile sole. An 84-day growth trial was conducted, in which food was supplied to three triplicate groups of juvenile Senegalese sole (3g wet weight) at different schedules - diurnal, nocturnal and mixed. At the end of the growth trial, ammonia and urea excretion was assessed during a 24h cycle. Improved growth (1.3% vs. 0.9%day(-1), specific growth rate), higher nitrogen retention (0.35 vs. 0.27gNkg(-1)day(-1)), lower ammonia excretion (209 vs. 272mg N-NH(4)kg(-1)day(-1)) and lower total nitrogen excretion (278 vs. 352mgNkg(-1)day(-1)) were found in daytime-fed fish compared with night-fed fish. Fish in the mixed feeding regime showed intermediate values of ammonia and total nitrogen excretion, but did not differ from day-fed fish regarding the other parameters. Results indicate that juvenile sole at a period of their life cycle appear to use more efficiently dietary protein for somatic growth under a diurnal than under a nocturnal feeding regime. This suggest that at least during a time-window in the juvenile rearing a diurnal feeding regime might be more effective in the production of this species.