This study was conducted to evaluate the apparent availability and P and N excretion in rainbow trout (Oncorhynchus mykiss) using different inorganic phosphorus sources. With this goal, fish (153 ± 14.1 g) fed four inorganic P sources were assayed: monoammonium phosphate (MAP, NH4H2PO4), monosodium/monocalcium phosphate (SCP-2%, AQphos+, NaH2PO4/Ca(H2PO4)2·H2O in proportion 12/88), monosodium/monocalcium phosphate (SCP-5%, NaH2PO4/Ca(H2PO4)2·H2O in proportion 30/70) and monocalcium phosphate (MCP, Ca(H2PO4)2·H2O). Phosphorus (P) digestibility, in diets that included MAP and SCP-2% as inorganic phosphorus sources, were significantly higher than for SCP-5% and MCP sources. In relation to the P excretion pattern, independent of the diet, a peak at 6 h after feeding was registered, but at different levels depending on inorganic P sources. Fish fed an MAP diet excreted a higher amount of dissolved P in comparison with the rest of the inorganic P sources, although the total P losses were lower in MAP and SCP-2% (33.02% and 28.13, respectively) than in SCP-5% and MCP sources (43.35% and 47.83, respectively). Nitrogen (N) excretion was also studied, and the fish fed an SCP-5% diet provided lower values (15.8%) than MAP (28.0%). When N total wastes were calculated, SCP-2% and SCP-5% showed the lowest values (31.54 and 28.25%, respectively). In conclusion, based on P and N digestibility and excretion, the SCP-2% diet showed the best results from a nutritional and environmental point of view.

Fish (175 g of initial weight) were fed in triplicated groups with four diets formulated by 0% (FO 100), 75% (FO 25) and 100% (with and without probiotics, FO 0 and FO 0+) of fish oil replacement consisting of a mixture of linseed, sunflower and palm oils. After 109 days, growth and nutritional parameters were not affected by the treatment; however, fish fed with 0% of fish oil showed the lowest survival rate and without differences between the same diet with probiotics. As for biometric parameters, significant differences in the viscerosomatic index (VSI) were observed between fish fed the FO 0+ diet and the FO 100 and FO 25 diets. Results obtained from histological analysis did not detect inflammation in gut samples, while liver samples showed a remarkable steatosis in all four treatments. Total fish oil replacement produced a significant difference in the width of the lamina propria. The dietary inclusion of probiotics in the FO 0+ diet seems to favour a recovery of intestine histology. In addition, as fish oil substitution increased, the width of the lamina propria also increased. In conclusion, it is possible to affirm that the four diets administrated to Seriola dumerili did not compromise the correct development of the animals.

Gilthead sea bream (Sparus aurata) was raised in six individual recirculating aquaculture systems (RAS) whose biofilters’ performance was analyzed. Fish were fed with three different diets (a control diet, a fishmeal-based diet (FM), and a plant meal-based diet (VM)) and with three different feeding strategies (manual feeding to apparent satiation, automatic feeding with restricted ration, and auto-demand feeding). For every combination of diet and feeding strategy, the mean oxygen consumption, ammonia excretion, and ammonia removal rate were determined. Fish fed with the VM diet consumed the most oxygen (20.06 ± 1.80 gO2 consumed kg−1 day−1). There were significant differences in ammonia excretion depending on the protein content and protein efficiency of the diet, as well as depending on feeding strategy, which in turn affected ammonia removal rates. Fish fed by auto-demand feeders led to the highest mean ammonia removal rate (0.10 gN-TAN removed m−2 biofiltration area day−1), while not leading to peaks of high ammonia concentration in water, which preserve fish welfare and growth.

The present study was conducted to investigate the effects of dietary fish oil replacement with a mixture of vegetable oils and probiotic supplementation on plasma biochemical parameters, oxidative stress, and antioxidant ability of Seriola dumerili. Specimens with an initial weight of 175 g were used. Four feeds were formulated with 0% (FO-100), 75% (FO-25), and 100% (FO-0 and FO-0+ with the addition of Lactobacillus probiotics) substitution of fish oil with a mixture of linseed, sunflower, and palm oils. After 109 days, no significant differences were observed in the activity of antioxidant enzymes in the liver, foregut, and hindgut, only glucose-6-phosphate dehydrogenase activity in the liver was higher in the fish fed the FO-100 diet than in those fed the FO-0 diet. No significant differences were observed in the total, reduced, and oxidized glutathione and the oxidative stress index in the liver. In addition, lipid peroxidation in the liver and red muscle values were higher in the fish fed the FO-100 diet than in the fish fed the FO-0+ diet, however, the foregut of the fish fed the FO-100 diet presented lower values than that of the fish fed the FO replacement diet, with and without probiotics. There were significant differences in cholesterol levels in the FO-100 group; they were significantly higher than those observed with the fish diets without fish oil. To sum up, fish oil can be replaced by up to 25% with vegetable oils in diets for Seriola dumerili juveniles, but total fish oil substitution is not feasible because it causes poor survival. The inclusion of probiotics in the FO-0+ diet had no effects on the parameters measured.

Aquaculture of gilthead seabream (Sparus aurata L.) is carried out in 20 countries, and it is the principal species in production in the Mediterranean Sea. The aquaculture seabream harvest in Spain in 2019 was 13.521 t, and the total aquaculture production in Europe and the rest of the Mediterranean reached 252.406 t (Asociación Empresarial de Acuicultura de España [APROMAR], 2020), positioning it as a species of great economic importance for the aquaculture industry.With the rapid intensification of aquaculture production in the world, the demand for aquafeeds and their main protein ingredient, fishmeal (FM), is increasing exponentially, given that this raw material still remain the principal sources of high-quality protein utilized in feed for carnivorous fish. This continuous increase in demand, together with the decrease in the supply of FM, has led the aquaculture sector to the need to find new alternatives for partial or total FM replacement in fish diets, which should be economic, environmentally friendly, safe, sustainable and palatable for fish species (Shafique et al., 2021). Consequently, the aquaculture industry and academia