Abstract
Dried fish soluble (FS), produced as a by-product from processing of Pacific whiting (Merluccius productus), may complement soybean meal (SBM) in rainbow trout (Oncorhynchus mykiss) diet by alleviating the negative impacts of high SBM. This study evaluated strain-specific responses of rainbow trout to high-SBM diets supplemented with dried FS on growth, nutrient utilization, and fillet quality. In a 66-day trial, 600 fish (22.1 g) were assigned to 10 treatments (in triplicates, 20 fish/tank) under 2 × 5 factorial design, testing two strains (in-house Hagerman and Commercial) and five diets: FM (fishmeal-based), SBM20 (20% SBM), SBM35 (35% SBM), SBM20 + FS5 (20% SBM + 5% dried FS), and SBM35 + FS5 (35% SBM + 5% dried FS). All diets were isonitrogenous (45% crude protein) and isolipidic (13%) and fed to satiation twice daily. At trial end, fillets were stored on ice for quality assessment on Days 1 and 8. The SBM35 + FS5 fish showed significantly higher growth (p < 0.05) than others. Daily feed intake was significantly improved by supplementing 5% FS in SBM35, without any difference in feed conversion and protein efficiency ratios. The commercial strain showed better growth performance than the Hagerman strain. Fillet yield was significantly higher in SBM35 + FS5. Diet, strain, and storage time significantly influenced fillet quality. Specifically, fillet textural resilience and pH were higher and liquid loss was lower in SBM35 + FS5 during 8-day storage. Unlike growth, the Hagerman strain retained better fillet quality parameters than the commercial strain. Conclusively, supplementing 5% dried FS in high SBM diet may improve growth performance and fillet quality.