Long photoperiod delayed spawning and increased somatic growth in giltheadseabream (Sparus aurata)

The effects of extended photoperiods. mimicking the longest day of the year , were studied in 1- and 2-year seabream. The photoperiod regimes started i n late July, 36 and 39 days after the summer solstice and continued for I I months. well beyond the natural reproductive season of December-March. Reg ime I (long day, 15.5L-:8.5D), which used natural and fluorescent light, re duced the incidence of maturity in both year classes and females did not sp awn although some gonadal development was observed. Among all 1-year sample d fish of regime 1, a maximum of 5% became spermiating males (March) and 5% reached the yolk granule stage of vitellogenesis (VO3; 250-400 mum diamete r) by May. Among 2-year sampled fish of regime 1, 45% became spermiating ma les and 25% were females, which reached the advanced vitellogenesis stage ( VO4; 400-600 mum) by April. Regime 2 (skeleton photoperiod), consisting of natural light and a 1.5-h pulse of fluorescent light during the period 14-1 5.5 h after sunrise, postponed gonadal development and spawning for up to 3 months. In this regime, a maximum of 80% of 1-year sampled fish were sperm iating males in February and a maximum of 10% were VO3 stage females in Mar ch. In the sampled 2-year fish, the maximum levels were 50% spermiating mal es in February and 25% VO3 stage females in March. Control fish, which were exposed to the natural photoperiod (29 degrees 34'N), spawned during their natural season. The maximum levels for I-year sampled control fish were 95 % spermiating males and no females in December, while among 2-year sampled fish, maxima of 75% males in February and 45% VO4 stage females in November . Final average weights of photoperiod treated fish (1-year = 430 g-regime 1, 400 g-regime 2; 2-year = 582 g -regime 1. 518 g-regime 2) were significa ntly greater (p < 0.05) than control fish (1-year = 341 g; 2-year = 476 g), Daily feed consumption (g/100 g fish) dropped from an average of 1.83 to 0 .93 g for 1-year fish during August-December and from 0.88 to 0.54 g for 2- year fish during the same period. This was correlated with reduced autumn a nd winter water temperatures (26-20<degrees>C summer to winter change) and increased fish weight in all treatments. Daily feed consumption was also af fected by the onset of spawning in the control and regime 2 (skeleton photo period) treatments of both 1- and 2-year fish. The efficiency of feed utili zation (FCR) and protein and energy retention were all affected by the phot operiod regimes and followed the same pattern of decrease as weight gain, r egime 1 (long day) > regime 2 (skeleton photoperiod) > control. (C) 2001 El sevier Science B.V. All rights reserved.