Long photoperiod on sea cages delays timing of first spermiation and enhances growth 1 in male

12 Two large groups of fingerling (3.2g) male European sea bass (around 75,000 13 individuals each) reared in net sea cages for a period of two years were exposed to two 14 different photoperiods starting in June: either ambient photoperiod (37o 24 ́ N) (NP) or a 15 constant long photoperiod (LP; 18 hours light: 6 hours dark, 18L: 6D). Long days had limited 16 effect on somatic growth at the time of incipient gonad development (IGD, 1 st annual cycle; 17 November-March), while they were effective at the time of full gonad development (FGD, 2 nd 18 annual cycle). Moreover, the annual patterns of morphological indices, i.e., Fulton’s condition 19 factor (CF), visceral fat index (VFI) and particularly gonadosomatic index (GSI), were 20 delayed by one or two months as the result of the long days compared to the control group 21 (NP). LP did not prevent the onset of puberty but delayed spermiation by one month, and 22 modified accordingly the phase and/or amplitude of the annual rhythms of pituitary 23 Gonadotropin Releasing Hormone (sbGnRH) content and plasma levels of Luteinising 24 Hormone (LH) and sex steroids, particularly that of 11-Ketotestosterone (11-KT). In general, 25 high levels of sbGnRH (≥4 ng/pit) were associated with elevated plasma LH (1-3 ng/ml at 26 *Manuscript