Influence of daylength on the age at first maturity and somatic growth in male sea bass (Dicentrarchus labrax, L.)

Groups of 4-month-old sea bass were each exposed over three consecutive yea rs to a natural photoperiod (40 degreesN) (NP), constant long photoperiod ( 15L:9D) (LO) and 18-month-expanded photoperiod (the natural light cycle ext ended to 18 months) (EX), under natural conditions of temperature (12.0-26. 3 degreesC). During the differentiation period, a significant increase in n umber of precocious males was found in the LO (26.8%) and EX (17.7%) groups compared to controls (5.3%) (P < 0.05), During the first reproductive seas on (20-25 months of age) gonadal size (GSI) in both the LO (0.82 <plus/minu s> 0.16%) and the EX (0.28 +/- 0.07%) groups was significantly lower than c ontrols (1.28 +/- 0.41%). The percentage of spermiating males during the fi rst reproductive period was lower in LO (< 60%) and EX (< 35%) groups compa red to controls (> 80%). At the second reproductive period (32-37 months of age) gonadal maturation was advanced in EX group, whereas a significant de lay was observed in LO group with respect to control. Spermiation in EX gro up was advanced with respect to control group. During the second reproducti ve period, percentage of spermiating males was significantly higher in EX g roup (similar to 80%) than in LO group (< 50%). LO and EX groups displayed enhanced growth (655.52 <plus/minus> 37.21 g and 376.40 +/- 6.33 mm; 510.44 +/-. 25.80 g and 350.14 +/- 5.27 mm, respectively) compared to controls (4 59.93 +/- 21.20 g and 343.62 +/- 4.82 mm). The present results indicate a s ignificant beneficial effect of constant long and expanded photoperiods on reducing sea bass gonadal development and enhancing growth at the age of co mmercialisation, with a potential application in aquaculture. (C) 2001 Else vier Science B.V. All rights reserved.