Use of Atlantic bluefin tuna (Thunnus thynnus) by-products in aquafeeds: trials with Dicentrarchus labrax and Litopenaeus vannamei

Global tuna catches reached a record 9.3 million tonnes in 2024, and processing generates by-products estimated at up to 55% of the fish biomass. This study tested whether meal from farmed Atlantic bluefin tuna (Thunnus thynnus) by-products (TBM), processed within 8 h of harvest, is equally suitable for two species with contrasting digestive physiology: the carnivorous European seabass (Dicentrarchus labrax) and the omnivorous whiteleg shrimp (Litopenaeus vannamei). For each species, four isonitrogenous, isolipidic diets replaced 0, 10, 20 and 50% of fishmeal with TBM. Each diet was tested in triplicate in recirculating systems: seabass (initial weight 17.50 g, 100 per tank, 10 weeks) and shrimp (3.15–3.18 g, 60 per tank, 4 weeks), fed to satiation four times daily; data were analysed by one-way ANOVA and Tukey HSD (p<0.05).

Seabass tolerated all inclusion levels: final body weights were 69.43±2.64, 69.36±3.33, 67.36±3.83 and 65.82±1.84 g and FCR 1.25±0.01, 1.25±0.01, 1.27±0.02 and 1.27±0.01 for the control, 10, 20 and 50% TBM diets. SGR (1.95–2.03% day⁻¹), PER (1.77–1.79), survival (>99%), condition factor K (1.29–1.34), viscera VSI (12.38–13.03% of body weight), liver HSI (2.35–2.55%) and whole-body protein CP (16.27–17.07%) and fat CF (14.13–15.10%) were unaffected.

Shrimp responded negatively: final body weight fell from 13.29±0.01 g to 12.70±0.45, 12.74±0.63 and 11.33±0.06 g, the lowest value differing significantly from all other diets. FCR rose from 0.87±0.02 to 0.94±0.04, 0.97±0.03 and 1.09±0.01 and PER declined from 2.65±0.06 to 2.49±0.12, 2.44±0.06 and 2.19±0.03, both differing significantly from the control at 20 and 50% TBM. SGR was significantly reduced only at 50% TBM, where feed intake was significantly higher than in the control, indicating impaired utilisation rather than reduced palatability; survival exceeded 94%. The same ingredient is therefore fully acceptable to a marine finfish yet limiting to a penaeid shrimp above 10% inclusion. This species-specific contrast has direct implications for by-product valorisation in Mediterranean aquaculture.