Effects of Dietary Lipid Levels on Growth and Gonad Development of <i>Onychostoma macrolepis</i> Broodfish

To assess the lipid requirements of O. macrolepis broodstock, five iso-nitrogenous diets (39 g kg⁻¹) with five lipid levels, 50 (5 L), 70 (7 L), 90 (9 L),110 (11 L), and 130 (13 L; g kg⁻¹), were made. A total of 105 three-year-old individuals (50.11 ± 2.86 g per fish) were divided into five groups (triplicate per group) and were fed with the diets, respectively, for eight weeks. Then, the fish were sampled, and items were determined. The results showed that growth rate and feed efficiency ratio were not significantly affected by diets (<i>p</i> > 0.05). A clear dose–response effect of dietary lipid was observed on somatic indexes of gonad indexes of the O. macrolepis brookstock, with the highest values corresponding to fish fed 9 and 11 g kg⁻¹ lipids, in contrast, gonad indexes were reduced as dietary lipid moved away from this level. The other somatic indexes, such as viscerosomatic index, perivisceral fat index, etc., were not significantly affected by diets (<i>p</i> > 0.05). The content of crude lipid and crude protein in carcass, hepatopancreas, and gonad were not significantly affected by dietary lipid levels (<i>p</i> > 0.05). The gonad fatty acids of 16:0 and 22:6n-3 decreased and 18:2n-6 increased with the increasing lipid level, being significantly altered by diets (<i>p</i> < 0.05). The histological features of the gonad showed no significant difference among the five diets (<i>p</i> > 0.05). The relative expression of sex steroid-synthesizing proteins (fshr, 3β-hsd, 17β-hsd, aro., and star.) in the gonad of fish was most significantly highly expressed in the 9 L and 11 L groups (<i>p</i> < 0.05). The results suggested that a proper dietary lipid level of 90–110 g kg⁻¹ could maintain gonad development of O. macrolepis broodstock without affecting growth performance.