A trial was performed to study the effects of a partially defatted Hermetia illucens (L. 1758) larvae meal (HIM) to replace a fish meal in the diet of an adult gilthead sea bream. The fish were fed for 120days with diets containing HIM: 0 (CTRL), 25 (HI25), 50 (HI50), and 75 (HI75), corresponding to inclusion levels of 0, 9.2, 18.4, and 27.6. A digestibility trial was carried out to evaluate the apparent digestibility coefficients (ADC). Growth performance, morphometric and biometric indexes, gill cortisol, status of gut mucosa, and the gut enzymes (alkaline proteases, lipase, and amylase) activity were evaluated. Morphometric and biometric indexes, digestibility, gill cortisol, and gut enzymes were not affected by the diet. Conversely, the 27.6 HI inclusion level worsened the specific growth rate, feed conversion ratio, and protein efficiency ratio. Histology showed no significant differences between CTRL and HI25 groups. Conversely, in many of HI50 and HI75 fish, anatomo-functional changes in the gut were observed. No statistical differences were found among diets for ADC of dry matter, crude protein, ether extract, and gross energy. The results showed that defatted HIM can be used as an alternative protein source up to 18.4 of the inclusion level without impacting the growth performance, gill cortisol, morphometric and biometric indexes, ADCs, and gut enzymes.

Over the last decades, an insect meal has received great attention for finfish diets, due to its nutritional composition and low ecological footprint. In the present study, we assessed the response of gut microbiota composition and liver histology of gilthead seabream (Sparus aurata) fed four experimental diets including the black soldier fly (Hermetia illucens) meal (HI) used to replace 0 (HI0), 25 (HI25), 35 (HI35) and 50 (HI50) percent of fish meal in a 131-day feeding trial. At the end of the experiment, a remarkable change in gut microbiota composition related to HI inclusion was observed, with a preponderance of Cyanobacteriain the control and low HI groups (HI0, HI25) while Chloroflexi became prevalent in the higher HI inclusion groups (HI35, HI50). Predictive analysis on bacterial metabolic pathways showed a clear separation between HI0–HI25 and HI35–HI50 groups. The microbiota shifts observed suggest a pivotal role of HI in inducing a bacterial-mediated physiological response in this fish species, probably due to chitin content and the fatty acid profile of this ingredient. Liver histology showed a higher hepatocyte size in fish from the HI50 group, suggesting lipid dysmetabolism due to the HI meal fatty acid profile, while a marginal adaptive response was observed in the HI25 group. In conclusion, while up to 25% inclusion of black soldier fly meal showed limited adverse effects, 50% HI dietary inclusion is not recommended in gilthead seabream diet, since possible alteration in lipid deposition, particularly at hepatic level, were highlighted in this fish species.

The present study has been aimed at evaluating the effects of the dietary inclusion of the live yeasts, Saccharomyces cerevisiae var. boulardii (LSB) administered at increasing concentrations (0, 100, and 300 mg kg⁻¹ of feed, here referred to as LSB 0, 100, 300) for 90 days, on the health conditions of European sea bass. The main zootechnical parameters, histological and morphological analyses, innate immunity response parameters (intestinal cytokine expression, lysozyme content, spontaneous hemolytic and hemagglutinating activities, antibacterial activities, and peroxidase activity) were measured as fish welfare parameters. LSB did not impair either growth parameters or the morphometric indexes. LSB down-regulated interleukin-1β transcription in the distal gut of fish treated with 5.4 × 10⁵ CFU g⁻¹ (LSB100) for 21 days. The interleukin-6 mRNA level decreased significantly in the proximal gut for both doses of yeast, after 21 days of feeding; the gene expression of interleukin-6 was significantly lower in the sea bass fed 10.81 × 10⁵ CFU g⁻¹ (LSB300) probiotic. The levels of TNF-α mRNA were not influenced by probiotic supplementation. Increases, although not significant, in the hematological and immunological parameters were also recorded. The data collected in the present study suggests that an LSB-supplemented diet acts on the gut immune system of sea bass by modulating the expression of the key inflammatory genes.

Subadult flathead grey mullets (Mugil cephalus) were fed three experimental diets containing increasing percentages of partially defatted black soldier fly (Hermetia illucens, BSF) that proportionally replaced the protein sources in the reference diet. At the end of the feeding trial, fish growth and gut, liver and spleen histology were evaluated. BSF inclusion did not significantly affect growth performances in any dietary groups. However, Fulton’s condition factor was lower in fish who were fed diets with the highest replacement levels (15% and 20%; BSF15 and BSF20) compared to those fed the 10% replacement (BSF10) and the control diet (BSF0). Histological analyses revealed increased villi thickness and mucous cell proliferation in the intestine of fish from BSF10 and BSF15 groups. A significant worsening of intestinal condition was observed in fish from the BSF20 group. Liver histology was not affected, while a dose-dependent effect on spleen was observed in fish fed BSF inclusions. Despite the absence of enteritis signs, an increase in macrophages/like TNF-α+ cells in the intestine mucosa indicated immune stimulation in the BSF10 group. Results indicate, for the first time, a threshold for BSF meal inclusion in diets specifically formulated for flathead grey mullets. The BSF10 diet was optimal, as growth performance was not affected and intestine health improved at both morphological and innate immune system levels.

The increasing presence of abandoned, lost, or discarded fishing gear (ALDFG) on the seafloor is a major source of microplastics (MPs) pollution in coastal ecosystems. This study assessed the concentration, morphology, and chemical composition of MPs in surface sediments collected from Alicante and Benidorm, in the Valencian Community, eastern coast of Spain, Mediterranean Sea. Impacted sites with fishing nets were compared to control sites without nets. Two analytical techniques were used for polymer identification, depending on particle size: micro-Fourier Transform Infrared Spectroscopy (µFTIR) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR). The results showed significantly higher MPs concentrations in sites affected by ALDFG. The findings highlight a clear link between the presence of fishing nets and MPs accumulation in sediments. This underlines the urgent need for mitigation strategies and recovery of discarded fishing gear. This study addresses a gap in the literature regarding MPs contamination on rocky coastal substrates and calls for further research to assess the long-term ecotoxicological impacts on marine ecosystems.

Over the last decades, insect meal has received great attention for finfish diets, due to its nutritional composition and low ecological footprint. In the present study, we assessed the response of gut microbiota and liver histology of gilthead seabream (Sparus aurata) fed four experimental diets including black soldier fly (Hermetia illucens) meal (HI) used to replace 0 (HI0), 25 (HI25), 35 (HI35) and 50 (HI50) percent of fish meal in a 131-day feeding trial. At the end of the experiment, a remarkable change in gut microbiota composition related to HI inclusion was observed, with a preponderance of Nitrospirota in HI0 and HI25 and of Chloroflexi in HI35 and HI50 groups. Predictive analysis on bacterial metabolic pathways showed a clear separation between HI0-HI25 and HI35-HI50 groups. The microbiota shifts observed suggest a pivotal role of HI in inducing a bacterial-mediated physiological response in this fish species, probably due to chitin content and the fatty acid profile of this ingredient. Liver histology showed a higher hepatocyte size in fish from the HI50 group, while a marginal adaptive response was observed in the HI25 group. Overall, 50% HI dietary inclusion is not recommended, since possible alteration in lipid deposition, particularly at hepatic level, were highlighted in this fish species.