Long-term feeding of a maintenance ration affects the release of Igf-1 and leptin, and delays maturation in a male teleost fish, Dicentrarchus labrax L.

Male European sea bass were used to investigate the effects of long-term exposure (14 months) to a maintenance ration on body weight gain, muscle lipid content and maturity. To this end, a group of animals were fed to visual satiety (CT), whereas a second group (EX) was provided an amount of feed each month equal to 0.35% of the CT group's biomass. To determine how energy balance affects metabolic factors, the circulating levels of Igf-1 and leptin and changes in mRNA levels of igf-1, igf-2 and igf-3 in the gonad were analyzed. Feed restriction impacted fish growth, and the specific growth rate was higher in the CT group than in the EX group. Moreover, the condition factor decreased over time in the EX group. Muscle lipid content, HSI, MFI and GSI also decreased in the EX group, which displayed increased apoptosis and low spermatogonial proliferation. Consequently, fish exposed to the maintenance ration showed lower rates of spermiation and delayed testicular development. Overall, fish in the EX group exhibited lower plasma levels of Igf-1 and leptin than those of the CT group. Of note, both plasma and expression levels of igf-1 in September and mRNA levels of igf-2 and igf-3 in February decreased significantly in the EX group, coinciding with the beginning of gametogenesis and full spermiation in this species, respectively. These results indicate that fish under a maintenance ration apparently use stored energy to support at least a basal metabolism and preserve their reproduction, although growth is disrupted. In this line, we suggest that leptin might act as a permissive factor for reproductive function, while Igf-1 might control spermatogenesis in sea bass.