Effects of alternative and sustainable ingredients, insect meal, microalgae and protein and lipid from tuna cooking water, on meagre (Argyrosomus regius) growth, food conversion and muscle and liver composition

This study aimed to evaluate the effects of alternative feed ingredients: Insect meal (DI) using non-defatted meal obtained from Acheta domesticus, Microalgae (DM) using a mix of four marine microalgae ((Nannochloropsis gaditana, Tisochrysis lutea, Rhodomonas lens, Isochrysis galbana), Protein and oil from water of tuna canning process (DP&L) and a Mixture (DMix) of the three ingredients, on the growth, feed utilisation, digestibility and composition of meagre juveniles, and the results obtained were compared with a feed similar to a commercial feed used as a control (DC). Results show that the formulated alternative feeds had different effects on fish growth. DMix have a similar growth performance than the control, whereas the other treatments (DI, DM and DP&L) showed a lower final weight. Hepatosomatic and viscerosomatic indices did not show differences among the treatments. Muscle protein content was higher for fish fed with DMix group whereas lipids were significantly higher in DI. In the case of the liver, protein was higher in the liver of fish fed with DI, DM and DP&L, whereas lipids were higher in fish fed with DI and DM, a result that was confirmed with the results obtained in hepatocyte size and lipid accumulation. The nutritional value of the meagre muscle at the end of the study showed that meagre fed with DM and DI diets contained a significantly higher content of monounsaturated and n-6 PUFA, whereas fish from the groups fed with DP&L and DMix had a significantly higher content of DHA and n-3 PUFA with the liver showing similar results. In view of the results obtained, the ingredients assayed in this study might be used as alternative sources of protein and lipids in aquafeeds since no negative effects were detected neither on fish growth, muscle composition or final nutritional value, except in the case of the diet with microalgae (DM), which inclusion rate in the feed must be adjusted and needs more research.