Assessment of long-term effects of the macroalgae Ulva ohnoi included in diets on Senegalese sole (Solea senegalensis) fillet quality

Abstract

Macroalgae are a promising source of a vast variety of bioactive compounds with potential interest in aquaculture. In addition to their sustainable and renewable nature, numerous evidences have been reported pointing to positive effects on fish growth, nutrient utilization, and disease resistance. Nevertheless, the effects on fish quality objective parameters have been scarcely explored. In this study we assessed the influence of Ulva ohnoi included at low level (5%) in a diet for Senegalese sole (Solea senegalensis) on several quality attributes of fish (proximate analysis, texture profile analysis, lipid oxidation, fatty acid profile, pH, water holding capacity, and colour parameters). A 270-d feeding trial was carried out, in which juvenile animals were fed with an Ulva-enriched diet only for 90 d out of the total 270-d study. This enabled to evaluate whether the possible effects on fish were transitory or persistent at the end of the assay. Besides modest effects on fish growth at early stages, the differences attributable to Ulva supplementation were mostly focused on the lipid fraction, texture, and colour parameters. Thus, Ulva diet reduced muscle total lipid content and favoured muscle selective retention of n-3 polyunsaturated fatty acids (PUFA), not least eicosapentaenoic acid (EPA) and docosahexaenoic (DHA) acid, and also diminished lipid oxidation, especially after a period of frozen storage. In terms of consumers' acceptability, seaweed supplementation impacted favourably on fillet texture and colour attributes, namely by increasing lightness (L*) and yellowness (b*), whilst reducing redness (a*). These results are particularly remarkable taking into account that low inclusion level was considered (5%), and above all, that Ulva supplementation was interrupted after 90 d, but the effects mentioned persisted at least up to 270 d. These deferred long-term effects might well be of practical interest when it comes to modifying quality attributes of edible fish.