Inclusion of 10% seaweed meal in diets for juvenile and on-growing life stages of Senegalese sole (Solea senegalensis)

Abstract

The long-term inclusion of 10% seaweed meal (Ulva rigida and Undaria pinnatifida) was evaluated in diets for Senegalese sole (Solea senegalensis). Triplicate groups of fish with an initial body weight of 23 g were fed the experimental diets (ULVA and UNDARIA) and compared to fish fed a control diet with no seaweed included (CTRL), both in juvenile (after 5 months of feeding, up to 60 g) and on-growing stages (after 9 months of feeding, up to 160 g). In the early juvenile phase, the inclusion of seaweeds did not affect fish growth, but final body weight was significantly lower in on-growing fish fed the UNDARIA diet. Overall, growth performance was also reduced in fish fed the UNDARIA diet, with a significantly lower daily growth index. Whole-body composition and nutrient retention (% intake) remained unaffected by the dietary treatment, but by the end of the growth trial fish fed the UNDARIA diet had a significantly lower protein gain associated with significantly lower intestinal villi width. At the end of the experiment, fish fed the UNDARIA diet had a significantly higher iodine flesh content (375.7 μg kg−1) than those fed the CTRL (187.5 μg kg−1) or ULVA (199.3 μg kg−1) diets, whereas selenium content was similar in all groups of fish. In conclusion, U. rigida seems a valid ingredient for Senegalese sole diets without affecting fish growth or nutrient utilization. Undaria pinnatifida was an effective way of naturally fortifying the nutritional value of sole fillets for human consumption, but resulted in growth impairment, so a lower inclusion level should be further evaluated.