Replacement of fish meal by plant protein sources up to 75% induces good growth performance without affecting flesh quality in ongrowing Senegalese sole

Abstract The replacement of fish meal (FM) by increasing levels of plant protein (PP) sources 50% (PP50), 75% (PP75) and 100% (PP100) was compared to a control diet (FM) containing fish meal as the main protein source in ongrowing Senegalese sole (mean initial body weight:106 g ± 15). These four diets were isonitrogenous and isolipidic (54% crude protein and 9% crude fat on a dry matter basis). By the end of the growth trial, groups fed PP50 and PP75 had a final body weight and daily growth index (DGI) similar to the FM fed group (200 g and 0.8–0.9, respectively), whereas PP100 diet induced a significantly lower DGI (0.4). PP100 showed the highest feed conversion ratio (FCR) (2.4 vs 1.5) and the lowest protein gain (0.5 vs 0.9 g kg − 1 ABWday − 1 ). Nutrient intake of PP groups was statistically similar to the FM group. Apparent digestibility coefficients (ADCs) of nutrients did not differ significantly among treatments (p > 0.05) and all PP diets induced lower fecal P losses than the FM group (33%). The highest PP levels (PP75 and PP100) resulted in decreased whole body lipid contents, thought PP100 showed the highest HSI and liver total lipids. In all groups, liver was the major lipid storage organ (13.96–28.57% WW). Muscle lipid content was low (1.3–1.6% WW) and did not vary significantly among treatments. Polyunsaturated fatty acid (PUFA) levels in muscle were also similar amongst dietary treatments and the two highest replacement levels (PP75 and PP100) were still effective in producing an n-3 PUFA rich product (29–30% of total fatty acids (WW)) similar to the FM group (33% of total fatty acids (WW)). Docosahexaenoic acid (DHA) was selectively retained in muscle (17–21% of total fatty acids (WW)) and neither DHA/EPA (Eicosapentaenoic acid) nor EPA/ARA (Arachidonic acid) ratios were significantly affected (p > 0.05) by dietary treatments. The sensory evaluation of cooked slices showed that the replacement of marine protein sources (FM) by PP blends did not have a significant impact on the majority of the descriptors, though visual freshness and whiteness of the PP75 flesh yielded the highest scores. Our results indicate that ongrowing Senegalese sole can effectively use diets with high levels of PP sources, up to 75% of FM replacement, without impairing feed intake, growth performance and protein utilisation whilst preserving high n−3 PUFA and DHA flesh content.