The Effects of Dietary Fishmeal Substitution by Full‐Fat and Defatted <i>Zophobas morio</i> Larvae Meals on Juvenile Gilthead Seabream ( <i>Sparus aurata</i> ): An Integrative Approach

This study evaluated the dietary fishmeal substitution by full-fat (FF) and defatted (DF) <i>Zophobas morio</i> meals regarding growth, feed efficiency, proximate and fatty acid compositions, digestive enzymes activities, histology and midgut microbiota in gilthead seabream (<i>Sparus aurata</i>). Juveniles initially weighing 3.4 g were distributed to triplicate groups and fed at satiation six isonitrogenous (8.41%) and isocaloric (21 Mj/kg) diets for 100 days. An insect meal-free diet was the control (CTRL), two diets contained a FF <i>Z. morio</i> meal at 49 g/kg (FF-49) and 97 g/kg (FF-97), and three diets contained a DF <i>Z. morio</i> meal at 58 g/kg (DF-58), 116 g/kg (DF-116) and 174 g/kg (DF-174) at the expense of fishmeal. Neither the form nor the inclusion level of <i>Z. morio</i> meals affected the feed intake of fish denoting a similar acceptability to that of fishmeal. Fish survival, growth and feed efficiency were not impaired by all dietary inclusion levels of <i>Z. morio</i> meals. Proximate composition of fish was altered but without indicating a clear correlation with the form or inclusion level of <i>Z. morio</i>. Increasing inclusions of both forms of <i>Z. morio</i> meals tended to decrease 22:6n-3, 20:5n-3, 18:3n-3 and 18:2n-6 levels in fish tissues. All fish exhibited similar proteolytic enzyme activities, but the increasing inclusions of both insect meal forms led to gradual increases in the lipase and α-amylase activities indicating a compensatory mechanism for lipid and carbohydrate digestion. The use of <i>Z. morio</i> meals led to some mild histomorphological changes in the intestine and liver that were more pronounced in fish fed the FF form at the highest inclusion level. Midgut bacterial communities of the groups were similar and dominated by potentially beneficial members of <i>Saccharimonadales</i> and <i>Rhodobacteraceae</i>, except FF-97 fish that had high abundances of <i>Legionella</i>- and <i>Pandoraea</i>-like bacteria. To conclude, <i>Z. morio</i> meal, either FF or DF, is a suitable insect protein for fishmeal substitution towards more sustainable aquafeeds for <i>S. aurata</i>.