Dietary plant oils delay early sexual maturation compared with marine fish oil in male European seabass (Dicentrarchus labrax) - Effects on testis histology and key reproductive hormones

Sexual precocity in farmed European seabass is correlated to reduced growth and flesh quality, and is one of the major challenges for the industry. We evaluated the effects of one marine (M) and one plant (P) oil mix, supplemented at 2 dietary inclusion levels, low (LF) and high (HF), on sexual maturation of European sea bass males. The feeding experiment was conducted on maturing unsexed fish kept in indoor tanks at 10:14 LD photoperiod and reducing water temperatures from October to December. Fish performance of all the fish population, males and females, testis histology, blood hormone levels and gene expression of selected sexual maturation related hormones in the brain and testis of male fish were studied. European seabass males fed the marine oil diets had higher mRNA expressions levels of Cyp 11b, Cyp 19a and Kiss2 in both brain and testis tissues compared with male fish fed plant oil diets. Moreover, high expression of brain Kiss receptor gene (Kissr4) was found in males fed a plant oil diet suggesting a late recrudescence phase of maturation (stages III & IV) in these groups. Histological analyses of testis were in agreement with the hormone gene expression observations where male fish fed with plant oil diets were in early to mid-maturing phase (stages III-IV), while marine oil fed males were at mid to late maturing phase (stages IV-V). No significant effects were observed between the low or high dietary fat treatments. The present results suggest that supplementing diets with plant oils delays maturation in male European seabass.