Growth performance and nutrient utilisation of Senegalese sole fed vegetable oils in plant protein-rich diets from juvenile to market size

Abstract

Sustainable aquaculture is highly dependent on the optimization of aquafeeds in terms of production costs, environmental sustainability and nutritional value. Senegalese sole (Solea senegalensis) is a prized flatfish produced in Europe with demonstrated capacity to cope well with both vegetable protein and oil sources. However, the total replacement of fish oil (FO) in diets with a high inclusion of plant proteins (PP) has never been assessed before in this species. Three extruded isoenergetic (23 KJ/g) and isolipidic (15% DM) practical PP-based diets (75% PP) were formulated: a control diet with fish oil (FO) and two experimental diets with 50% and 100% inclusion of a vegetable oil (VO) blend to replace FO (VO50 and VO100). Triplicate groups of fish (13.3 ± 0.9 g) were kept in a recirculation saltwater system at 19 °C and fed the experimental diets ad libitum during 18 months. Fish were sampled after 6 and 18 months (in juvenile and on-growing developmental stages, respectively). The total substitution of FO by VO (VO100) during the juvenile phase (6 months of feeding) significantly reduced final body weight, daily growth index, and protein gain, and increased FCR. A longer feeding period (after 18 months) showed that VO inclusion had no major effects on fish growth, but FCR was still significantly higher in fish fed VO100 than in FO. At the end of the trial, muscle saturated FA level decreased with increasing dietary VO, whereas monounsaturated and polyunsaturated FA levels increased in fish fed VO diets particularly due to increased levels of linoleic, α-linoleic and arachidonic acid acids. In conclusion, the long-term replacement of marine ingredients by VO and PP sources does not impair Senegalese sole growth, but strongly reduces EPA + DHA muscle levels, compromising the nutritional value of fillets for human consumption.