K. Pichavant, J. Person Le Ruyet, A. Severe, A. Le Roux, L. Quemener, G. Boeuf-1998
Bulletin Francais de la Peche et de la Pisciculture, (350-51) : 265-277 (from Current Contents)
Abstract:
Turbot juveniles (32 g of artificial photoperiods : four constant photoperiod regimes (8L:16D, 12L:12D, 16L:8D, 24L:0D) and two changing regimes, one increasing from 12 to 16 h light per day, and the other decreasing from 12 to 8 h light per day. All other environmental conditions were maintained constant: temperature : 17 +/- 0.5 degrees C, salinity : 34.5 ppt, light intensity : 2 W.m(-2), O-2 over 6 mg/l. The effects of these photoperiods on growth, feed efficiency, nitrogenous excretion, physiological status (blood plasma osmolarity, chloride, sodium, potassium and thyroid hormones contents) were studied. All over the experiment, fish looked healthy and no mortality was observed. No significant differences in growth response to photoperiod were observed. Specific growth rate (1.7-1.9), apparent food conversion ratio (0.70-0.75), protein efficiency ratio (2.5-2.7) and protein utilization coefficient (36-39 %) were not photoperiod-dependent. There were no changes in fish body composition in terms of proteins, lipids, ash and water contents. No significant differences in blood plasma osmolarity, chloride, sodium and potassium concentrations, related to photoperiods, were observed. T-4 concentrations were similar for all photoperiods tested, they ranged from 2 to 4 ng/ml while T-3 levels significantly decreased at the end of experiment in turbot maintained under the shortest day-lengths (8 hours light and decreasing photophase). A major post-prandial increase in total ammonia nitrogen excretion was observed under photophases 8 h, 12 h and 16 h. Under permanent lighting, this peak was significantly lower. Urea nitrogen excretion showed a nocturnal peak related to photoperiod. In fish submitted to permanent lighting, the same urea pattern was observed. In the Atlantic strain of turbot tested, growth and feed efficiency were not influenced by photoperiod at least within 60 days.
(IFREMER, Physiol Poissons Lab, BP 70, F-29280 Plouzane, France)