This study examined the growth performance, cellular signaling, and gut microbiome of gilthead sea bream ( Sparus aurata ) fed four diets using low‐trophic‐level ingredients for 65 days. Control (C) diet contained fish meal (FM) as the main protein source and fish oil (FO) as a lipid source. In the 0%FMFO diet all FM and FO present in the C diet was replaced with a combination of microalgae, insect meal (IM), and tunicate meal (TM). IM and TM diets were formulated to contain 20% of the novel protein ingredients, replacing 68.09% and 45.91% of FM in diet C, respectively. Compared to diet C, feed utilization and growth performance of S . aurata fed 0%FMFO diet was not different ( p > 0.05) and TM diet had a significantly lower ( p < 0.05) specific growth rate (SGR), higher ( p < 0.05) feed conversion ratio (FCR) and decreased fillet lipid content ( p < 0.05). In liver and foregut of fish fed TM diet the activity of lactate dehydrogenase (L‐LDH) significant increased ( p < 0.05), indicating higher glycolytic potential, whereas the decrease in Hsp70, Hsp90, AMPK, and p38 MAPK may indicate reduced stress response. Fish midgut microbiome included beneficial taxa for the host. The results suggested that the mixture of algae, insect, and TM could replace all FM and FO in gilthead sea bream diets without affecting the fish growth performance.

Brackish aquaponics is expected to be a promising approach to sustainable food production, integrating saline water resources with simultaneous co-cultivation of fish and halophytes. The present study investigated the effects of three feeding ratios (FR1.5: 1.5%, FR3: 3%, and FR6: 6% b.w/d) on the growth performance of European sea bass (Dicentrarchus labrax) and glasswort (Salicornia europaea) co-cultured in three autonomous one-loop recirculation aquaponic systems (180 L each) at 20 ppt salinity over 78 days. Each system comprised three fish-rearing tanks connected to a two-stage sump filter and a nutrient film technique (NFT) hydroponic subsystem. Sea bass fed at FR3 achieved significantly higher weight gain, specific growth rate, and feed conversion efficiency than FR1.5. At FR6, feed consumption nearly doubled compared to FR3 (3.79 vs. 1.91 g), yet the feed conversion ratio increased from 0.79 to 1.65, and protein efficiency ratio declined from 3.80 to 1.91, indicating overfeeding effects. Regarding glasswort, FR6 produced significantly higher chlorophyll a content and plant biomass, whereas FR1.5 showed superior ammonia removal efficiency. Overall, FR3 provided the best balance between fish growth, plant yield, and water quality maintenance. These findings highlight the critical role of feeding management in brackish aquaponics in order to optimize nutrient coupling between fish and halophyte production.

The aim of this study was to evaluate the impact of two sustainable dietary protein sources on the structure and composition of the gut microbiota in European sea bass (Dicentrarchus labrax) juveniles. These protein sources were incorporated to the aquafeeds containing (a) Lupinus albus meal, treated with either exogenous enzymes (Solid state hydrolysis-SSH) or fermented with Saccharomyces cerevisiae (Solid state fermentation, SSF) and (b) Lagocephalus sceleratus meal. In the first case (a), the control aquafeed simulated a standard commercial diet, containing soybean meal whereas in the rest of the diets soybean meal was partially or totally replaced by hydrolysed or fermented Lupin meal. In the second case (b) the fish were fed Lagocephalus sceleratus unprocessed fishmeal as well as treated at different temperatures to deactivate tetrodotoxin (TTX). A control diet with 30% commercial fish meal was also fed as a reference diet. Both diets in all inclusion levels did not cause any significant gut microbiota change, suggesting their neutral role in this aspect. However, the gut bacterial communities of the fish fed with 12.5% lupin meal inclusion, had increased amino acid biosynthetic pathways suggesting a beneficial effect.