Effects of ration level on growth performance, feed utilization and energy budget of juvenile triploid turbot (Scophthalmus maximus)

Feed ration is a key manageable factor influencing growth performance and production costs in aquaculture. This study evaluated the effects of feeding level on growth performance, feed utilization, digestibility, and energy allocation in juvenile triploid turbot (Scophthalmus maximus) to establish an optimal feeding strategy. Triploid juveniles (42.62 ± 2.79 g) were fed six ration levels (50, 60, 70, 80, 90, and 100% of satiation, with 100% corresponding to 1.4% body weight d⁻¹) for 60 days. Weight gain and specific growth rates increased significantly with ration up to 80% satiation, after which they plateaued. All specific growth rates (wet weight, dry weight, protein, and energy) exhibited significant quadratic relationships with ration level, with maximum growth predicted at 87.5–93.8% satiation. Energy-based feed conversion efficiency peaked at 70% satiation, with an optimum of 73.5% satiation determined by quadratic regression. Apparent digestibility coefficients for dry matter, protein, and energy increased progressively, reaching their highest values at 90% satiation. Nitrogenous excretion and faecal production showed strong linear relationships with ration level. The proportion of ingested energy allocated to growth was maximized (28.94 ± 0.34%), and metabolic energy expenditure minimized (56.83 ± 0.34%), at 70% satiation. The optimal energy budget at this ration was: 100.0C = 28.9G + 4.7F + 9.5U + 56.8R. Integrating growth performance and feed efficiency, the optimal ration range for juvenile triploid turbot is 73.5–87.5% of satiation. This range balances growth maximization, feed efficiency, and waste reduction. These findings provide a scientific basis for developing ploidy-specific feeding protocols to improve production efficiency and reduce environmental impacts in triploid turbot aquaculture.