The influence of a longer photoperiod on growth parameters of European sea bass Dicentrarchus labrax (Linnaeus, 1758) reared in sea cages

Summary The aim of this study was to investigate the effects of a long‐term photoperiod (15L : 9D) on both the somatic growth and husbandry parameters of sea bass Dicentrarchus labrax . Experiments were conducted in triplicate in high density polyethylene ( HDPE ) floating cages with net depths of 14 m and diameters of 20 m. Experiments were performed with approximately 170 000 sea bass with initial average weights of 110.63 ± 3.12 g and 110.26 ± 29.70 g for the experimental and control groups, respectively. Beginning in April 2008, extended artificial lighting was used in the experimental cages for 13 months; the control group received no additional illumination. At the end of the experiments, the average weights of the experimental and control groups were 362.13 ± 7.72 and 310.34 ± 18.15 g, respectively. Specific growth rate ( SGR ) was relatively high in the experimental group compared to the control fish. Feed conversion ratio ( FCR ) was 2.02 and 2.21 for the experimental and control groups, respectively, with significant differences also found between these groups (P   <   0.05). Moreover, gonadal fish weight in the control group was significantly higher than in the experimental group, with the gonadosomatic index fluctuating within a 1.71‐fold increase.