Abstract Background Aquaculture, traditionally a form of biotechnology, has evolved to integrate innovative biotechnological applications, such as advanced feed formulations, aimed at improving the growth performance and health of farmed fish species. In the present study, the effects of feeding rainbow trout with novel feed formulations were investigated. Fish growth, gut and liver morphology, the concentration of fatty acids in the fillet, and volatile fatty acids in the gut were assessed. The study also validated scenarios from in vivo experiments using a nutrient-based model called FEEDNETICS™. This globally used model serves as a tool for data interpretation and decision support in the context of precision fish farming. Methods Alternative protein and oil sources, including poultry by-product meal (PBM) and natural algae oil, were explored as sustainable replacements for fishmeal (FM) and fish oil (FO). A 90-day feeding trial was conducted using rainbow trout, comparing two isoproteic, isolipidic and isoenergetic diets. The control diet contained 15% FM, 5% PBM, and 8% FO, while the test diet replaced FM with 15% PBM and 5% feather meal hydrolysate (FMH), and fully substituted FO with VeraMaris® natural algae oil and rapeseed oil. Results PBM successfully replaced FM protein without negatively affecting feed intake, growth performance or feed utilization in trout. The combination of PBM and natural algae oil was well tolerated by the trout and showed no negative effects on gut health. A detailed analysis of fatty acids in the fillet revealed that PUFAs of the n3 and n6 series were significantly higher in the PBM group than in the FM group. Values of fatty acid-related health indexes, including atherogenicity index, and thrombogenicity index, confirmed the high nutritional value of trout filet, thus representing a healthy product for human. In addition, the predictions using the FEEDNETICS™ indicated that the tested novel alternative formulations are economically viable. The validation of the model for fish growth resulted in a Mean Absolute Percentage Error (MAPE) of 8%. Conclusions The FEEDNETICS™ application enhances our ability to optimize feeding strategies and improve production efficiency in the aquaculture industry. VeraMaris® algae oil and PBM could serve as viable and sustainable raw materials for fish feed, promoting environmentally friendly aquaculture practices.

As a result of evolution, many biological materials have developed irregular structures that lead to outstanding mechanical performances, like high stiffness-to-weight ratios and good energy absorption. However, reproducing these irregular biological structures in synthetic materials remains a complex design and fabrication challenge. Here, a bioinspired material design method is presented that characterizes the irregular structure as a network of building blocks, also known as tiles, and rules to connect them. Rather than replicating the biological structure one-to-one, synthetic materials are generated with the same distributions of tiles and connectivity rules as the biological material and it is shown that these equivalent materials have structure-to-property relationships similar to the biological ones. To demonstrate the method, the pericarp of the orange, a member of the citrus family known for its protective, energy-absorbing capabilities is studied. Polymer samples are generated and characterized under quasistatic and dynamic compression and display spatially-varying stiffness and good energy absorption, as seen in the biological materials. By quantifying which tiles and connectivity rules locally deform in response to loading, it is also determined how to spatially control the stiffness and energy absorption.

In the present study, gilthead sea bream (Sparus aurata) was reared using sustainable feeds containing insect meal from Hermetia illucens larvae. Proteomics and proton nuclear magnetic resonance-based metabolomics analysis were used to assess the metabolic impact of the tested feeds in sea bream liver, whereas the composition of muscle fillets was characterized by means of metabolomics and gas chromatography of fatty acid methyl esters. Including 10% of insect meal while correspondingly reducing fish meal did not substantially alter the metabolism of dietary nutrients, leading to small but significant effects solely on lauric acid content of sea bream fillets. Furthermore, a few alterations in some markers of immune response, such as leukocyte elastase inhibitor-like, granzyme B (G, H)-like, and two associated ortholog groups, serpin B and chymase, were found. In the fish group fed with insect meal, liver morphology analysis showed no structural damage or inflammation and a lower amount of hepatic lipid deposition and accumulation.

Aquaculture is one of the world's fastest growing food-producing sectors, providing more than half of all fish consumed globally for human nutrition. However, to maintain such growth and meet the increasing demand for aquatic food, sustainable raw materials for fish feeds are needed. In this regard, insects represent one of the most promising alternatives to fish meal (FM) protein source for use in aquafeeds. In addition to protein, insects contain bioactive compounds, such as chitin, which is a natural polysaccharide abundantly present in the pupal exuviae of some insects. Studies have shown that dietary chitin or its derivate chitosan acts as a prebiotic thus modulating the gut microbial communities of fish. Accordingly, the present study aimed to evaluate the effect of two waste products rich in chitin, i.e., shrimp head meal (SHM), and insect (Hermetia illucens) pupal exuviae on the gut microbiota of rainbow trout (Oncorhynchus mykiss). Three isoproteic, isolipidic, and isoenergetic diets containing either FM, SHD, or a combination of FM and 1.6% of pupal exuviae meal (PEM) were tested through a 91-day feeding trial. At the end of the experiment, no differences in final mean body weight, specific growth rate, and feed conversion ratio values were observed between fish experimental groups. Mortality was <1% and it did not correlate with diet for the entire duration of the trial. However, a modulatory effect of dietary pupal exuviae on fish gut microbiota was detected. Indeed, gut bacterial species richness improved by including insect exuviae. In particular, Firmicutes and Actinobacteria phyla, mainly represented by Bacillus, Facklamia, Brevibacterium, and Corynebacterium genera, were enriched in trout receiving pupal exuviae. These genera are chitinolytic and short-chain fatty acids (SCFAs)-producing bacteria. SCFAs production was confirmed by gas chromatography analysis, which detected the highest amount of butyrate in feces of trout fed with pupal exuviae meal. Functional inference analysis of intestinal microbiota using PICRUST metagenome prediction tool, showed differences in response to diet. In particular, eleven pathways were significantly different between control fish (FM) and fish fed the PEM diet, whereas twenty functional traits were significantly different between the FM and SHM fish groups. Overall, our data confirmed that chitin from insect's pupal exuviae represents a promising functional ingredient, better than SHM, for positively modulating gut microbiota communities of rainbow trout.

The sustainable development of modern aquaculture must rely on a significant reduction of the fish meal (FM) used in aquafeed formulations. However, FM substitution with alternative ingredients in diets for carnivorous fish species often showed reduced nutrient absorption, significantly perturbed metabolisms, and histological changes at both hepatic and intestinal levels. In the present study, rainbow trout (Oncorhynchus mykiss) were fed three different experimental aquafeeds. A control diet with higher FM content (27.3%) than two test formulations in which FM was substituted with two more sustainable and promising alternatives: insect meal (Hermetia illucens larvae = 10.1%, FM = 11.6%) and poultry by-products meal (PBM = 14.8%; FM = 11.7%). Combined metabolomics and proteomics analyses of fish liver, together with histological examination of liver and intestine demonstrated that a well-balanced formulation of nutrients in the three diets allowed high metabolic compatibility of either substitution, paving the way for a deeper understanding of the impact of novel raw materials for the fish feed industry. Results show that the main metabolic pathways of nutrient absorption and catabolism were essentially unaltered by alternative feed ingredients, and also histological alterations were negligible. It is demonstrated that the substitution of FM with sustainable alternatives does not have a negative impact on fish metabolism, as long as the nutritional requirements of rainbow trout are fulfilled.

With demands and reliance on aquaculture still growing, there are various challenges to allow sustainable growth and the shift from fishmeal (FM) to other protein sources in aquafeed formulations is one of the most important. In this regard, interest in the use of insect meal (IM) in aquafeeds has grown rapidly. Accordingly, the aim of the present study was to assess the effects of dietary IM from Hermetia illucens (Hi) larvae included in a low-FM diet on gut microbial communities of rainbow trout ( Oncorhynchus mykiss ), in terms of both composition and function of microbiome. A feeding trial was conducted using 192 trout of about 100-g mean initial weight. Fish were fed in quadruplicate (4 tanks/diet) for 131 days with two diets: the control (Ctrl) contained 20% of FM as well as other protein sources, whereas the Hi diet contained 15% of Hi larvae meal to replace 50% of the FM contained in the Ctrl diet. High-throughput sequencing of 16S rRNA gene was used to identify the major feed and gut bacterial taxa, whereas Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis was performed on gut bacterial genomes to identify the major active biological pathways. The inclusion of IM led to an increase in Firmicutes, mainly represented by Bacilli class and to a drastic reduction of Proteobacteria. Beneficial genera, such as Lactobacillus and Bacillus , were enriched in the gut of fish fed with the Hi diet, whereas the number of bacteria assigned to the pathogenic Aeromonas genus was drastically reduced in the same fish group. The metagenome functional data provided evidence that dietary IM inclusion can shape the metabolic activity of trout gut microbiota. In particular, intestinal microbiome of fish fed with IM may have the capacity to improve dietary carbohydrate utilization. Therefore, H. illucens meal is a promising protein source for trout nutrition, able to modulate gut microbial community by increasing the abundance of some bacteria taxa that are likely to play a key role in fish health.

Background Aquaculture must continue to reduce dependence on fishmeal (FM) and fishoil in feeds to ensure sustainable sector growth. Therefore, the use of novel aquaculture feed ingredients is growing. In this regard, insects can represent a new world of sustainable and protein-rich ingredients for farmed fish feeds. Accordingly, we investigated the effects of full replacement of FM with Tenebrio molitor (TM) larvae meal in the diet of rainbow trout (Oncorhynchus mykiss) on fish gut and skin microbiota. Methods A feeding trial was conducted with 126 trout of about 80 g mean initial weight that were fed for 22 weeks with two isonitrogenous, isolipidic, and isoenergetic extruded experimental diets. Partially defatted TM meal was included in one of the diets to replace 100% (TM 100) of FM, whereas the other diet (TM 0) was without TM. To analyse the microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and Qiime pipeline were used to identify bacteria in the gut and skin mucosa, and in the diets. Results The data showed no major effects of full FM substitution with TM meal on bacterial species richness and diversity in both, gut mucosa- and skin mucus-associated microbiome. Skin microbiome was dominated by phylum Proteobacteria and especially by Gammaproteobacteria class that constituted approximately half of the bacterial taxa found. The two dietary fish groups did not display distinctive features, except for a decrease in the relative abundance of Deefgea genus (family Neisseriaceae) in trout fed with insect meal. The metagenomic analysis of the gut mucosa indicated that Tenericutes was the most abundant phylum, regardless of the diet. Specifically, within this phylum, the Mollicutes, mainly represented by Mycoplasmataceae family, were the dominant class. However, we observed only a weak dietary modulation of intestinal bacterial communities. The only changes due to full FM replacement with TM meal were a decreased number of Proteobacteria and a reduced number of taxa assigned to Ruminococcaceae and Neisseriaceae families. Conclusions The data demonstrated that TM larvae meal is a valid alternative animal protein to replace FM in the aquafeeds. Only slight gut and skin microbiota changes occurred in rainbow trout after total FM replacement with insect meal. The mapping of the trout skin microbiota represents a novel contribution of the present study. Indeed, in contrast to the increasing knowledge on gut microbiota, the skin microbiota of major farmed fish species remains largely unmapped but it deserves thorough consideration.

Alternative nutrient sources to fishmeal for fish feed, such as insect meals, represent a promising sustainable supply. However, the consequences for fish digestive function have not been exhaustively investigated. In the present study we evaluated the effect of partial fishmeal substitution with 10% Hermetia illucens (Hi10) larvae meal on the neuromuscular function of proximal and distal intestine in gilthead sea bream. In animals fed with insect meal, weight and growth parameters were similar to controls fed with conventional fishmeal. In addition, no anomalies in intestinal gross morphology and no overt signs of inflammation were observed. The gastrointestinal transit was significantly reduced in Hi10 fed animals. In the proximal and distal intestine longitudinal muscle, Hi10 feeding downregulated the excitatory cholinergic and serotoninergic transmission. Sodium nitroprusside-induced inhibitory relaxations increased in the proximal intestine and decreased in the distal intestine after Hi10 meal. Changes in the excitatory and inhibitory components of peristalsis were associated with adaptive changes in the chemical coding of both proximal and distal intestine myenteric plexus. However, these neuromuscular function alterations were not associated with considerable variations in morphometric growth parameters, suggesting that 10% Hi meal may represent a tolerable alternative protein source for gilthead sea bream diets.

Using a circular economy concept, the present study investigated the use of crude glycerol, a primary by-product of biodiesel production, as a low-priced nutrient source for heterotrophic cultivation of the fungus-like protist Schizochytrium limacinum SR21 strain. The whole biomass of this oleaginous microorganism, rich in docosahexaenoic acid (DHA) and high-quality proteins, was then paired with a vegetable oil (VO) source and used to replace fish oil (FO) in European sea bass ( Dicentrarchus labrax ) feeds. Four nutritionally balanced diets were formulated: diet FO (a FO-based diet), diet VO + 0 (a VO-based diet without S. limacinum ), and diets VO + 5 and VO + 10 that were VO-based feeds supplemented with 5 and 10% of S. limacinum , respectively. After a 3-month feeding trial, fish of all dietary groups tripled their initial weight, but growth and feeding efficiencies of D. labrax were not significantly different among treatments. Although the formulated diets were balanced for polyunsaturated fatty acids (PUFAs), fish fed with feeds containing either VO or VO plus 5 and 10% of S. limacinum biomass had significantly higher levels of PUFAs in the flesh than fish fed the FO-based diet. Values of health-related lipid indexes, such as atherogenicity index, thrombogenicity index, and flesh lipid quality as well as n-6/n-3 and PUFAs/SFAs ratios confirmed the high nutritional value of sea bass filet, thus representing a healthy product for human consumption. Although the PUFAs/SFAs ratio showed a significantly higher value in fish fed with VO-based diets supplemented with S. limacinum than in those fed with FO diet, suggesting a better filet quality, the n-6/n-3 ratio clearly indicated that filet quality of dietary group FO was best (value of 0.55) and that of group VO + 10 second best (value of 0.98). We also evaluated the nutritional regulation of Δ6-desaturase (or fads2 ) gene expression in European sea bass liver. European sea bass fed the VO + 0 diet had the highest number of mRNA copies for Δ6-desaturase (or fads2 ), fish fed with diet VO + 10 the lowest. Our study adds to the growing body of literature concerning the use of thraustochytrid biomass as a valid alternative to marine-derived raw materials for European sea bass feeds.

The big advantage of using molecular biomarkers to monitor oxygen levels in aquatic systems is that responses at the molecular level tend to be more sensitive, and usually occur earlier than those at higher levels of biological organization Aquatic hypoxia is a frequent event, which can occur naturally in a variety of marine, estuarine and freshwater habitats. More often, however, hypoxia arises as a result of euthrophication of aquatic ecosystem and can lead to changes in community structure by eliminating hypoxia-sensitive species. Consequently fish have develop various physiological and biochemical mechanisms to cope with this environmental stress. Many of these adjustments depend to changes in expression of a wide range of genes. The transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor-1 (HIF-1), a heterodimer composed of an α and β subunit. This study investigated if HIF-1α mRNA levels were regulated by hypoxia in Eurasian perch (Perca fluviatilis), a hypoxia-sensitive fresh water species. The real-time PCR was utilized to monitor dynamic changes in levels of HIF-1α mRNA in response to acute (DO 0.4 ± 0.1 mg/l for 1 h) and chronic (DO 2.8 ± 0.3 mg/l for 15 days) hypoxia. Our results indicated an up-regulation of HIF-1α in brain and liver, but not in muscle tissue after acute hypoxic treatment, whereas significant changes of HIF-1α mRNA levels were detected in muscle, but not in brain and liver after chronic hypoxia exposure. This study suggests that HIF-1α mRNA level in selected perch tissues could be an useful indicator of acute exposure to hypoxia.

No data have previously been reported on Eurasian perch Perca fluviatilis L. in Lake Varese. In this study, the growth, diet, and reproductive biology of the Eurasian perch population were investigated with the aim of providing information that may serve as a basis for efficient resource management. A total of 240 specimens were caught during the monthly sampling campaign from November 2006 through October 2008. The length-to-weight relationships were W t = 8.4 × 10−3 L t 3.10 (males) and W t = 4.1 × 10−3 L t 3.36 (females). The parameters for the von Bertalanffy growth function for pooled sexes were L ∞  = 33.17 cm, k = 0.20 year−1, and t 0 = −1.34 year. Perch in Lake Varese spawn from April through May. Sexual maturity is reached when males are 2 years old, in females mostly when they are 3 years old. Relative fecundity (F rel) and absolute fecundity (F abs) were assessed for females. Fecundity values were similar to data reported for other European populations: females of age 2+ F rel = 102,457 ± 12,275, age 3+ F rel = 131,767 ± 5,891, and age 4+ F rel = 131,252 ± 15,555. Perch diet spectrum was wide and somewhat characterized by season. Perch in Lake Varese feed on macroinvertebrates, mainly Chironomidae and Chaoborus, zooplankton, and juvenile rudd Scardinius erythrophthalmus.

Eurasian perch (P. fluviatilis) is a very important fish species in Varese lake (N-W Italy). Since the second half of 20(th) century, perch catches in the lake have steadily decreased and by the end of the '80s the species resulted clearly endangered. The purpose of this study was to investigate growth, mortality and feeding conditions of perch post-larvae, reared in illuminated floating cage in Varese lake, to obtain fingerlings for a restocking program. In June 2006 and 2007, groups of 280 and 300 pre-weaned post-larvae (average body weight 0.64 +/- 0.09 g and 0.25 +/- 0.08 g respectively P<0.01) were held in an illuminated net cage for 90 days. The cage was illuminated inside from 20:30 p. m. to 6:30 a. m. During the trial, the nightly zooplankton accumulation inside the cage was assessed weekly. At night time the zooplankton biomass, which resulted dominated by Cladocera family, was higher inside the cage than in the lake. In 2006, 322 +/- 36 zooplankters L(-1) were observed, compared to 945 +/- 600 observed in 2007 (P<0.05). In the lake, the number of zooplankters per litre was similar in both years, resulting in 63.3 +/- 50.30 and 61.10 +/- 45 zooplankters L(-1), respectively on 2006 and 2007. In order to assess perch growth performances, 25 fishes were sampled from the cage every 15-20 days and length (cm) and weight (g) were assessed for each sample. At the end of September, specific growth rate (SGR) and survival rate were assessed. In 2006 the final mean body weight of the perch fry was 4.65 +/- 1.47 g and that results significantly lower (P<0.05) than of 2007 (6.3 +/- 1.69 g). The SGR was 2.04% and 3.42%, respectively. The higher growth rate observed in 2007 was influenced by a higher zooplankton accumulation in the cage due to an improved cage management. In order to assess the cage efficiency, in September 2006 and 2007, the weight of young-of-year perch (n=50) captured in the lake were compared to those of reared fish. Wild fry showed a mean body weight significantly higher (P<0.05) than reared ones (15.90 +/- 4.25 g and 17.86 +/- 4.47 g in 2006 and 2007, respectively). The survival percentages resulted 50.7% in 2006 and 60.7% in 2007. The results demonstrate that the rearing of perch in illuminated floating cages enables the possibility to produce fry for restocking programs in Varese lake.

Aquatic hypoxia is a frequent event and in fish a complex set of physiological and biochemical alterations are employed to cope with this environmental stress. Many of these adjustments depend to a large extent on changes in the expression of genes that encode for physiologically relevant proteins. Genes that are induced by hypoxia appear to share a common mode of transcriptional regulation. This induction depends upon activation of a transcription factor, the hypoxia inducible factor-1 (HIF-1), which is a heterodimer composed of two subunits: alpha and beta.In this study we report first on the molecular cloning and characterization of HIF-1 alpha in sea bass (Dicentrarchus labrax). The full-length sea bass cDNA for HIF-1 alpha was isolated and deposited in the GenBank with accession no. DQ171936. It consists of 3317 base pairs (bp) carrying a single open-reading frame that encompasses 2265 bp of the coding region and 1052 bp of the 3' UTR.We then utilized the real-time PCR technology to monitor dynamic changes in levels of HIF-1 alpha transcripts, in response to acute and chronic hypoxic stress. The number of HIF-1 alpha mRNA copies were significantly increased in response to both acute (1.9 mg/L, dissolved oxygen for 4 hours) and chronic (4.3 mg/L, DO for 15 days) hypoxia in sea bass, whereas it remained unchanged in fish exposed to hyperoxic (DO 13.5 +/- 1.2 mg/L, 155 % saturation) conditions. This is the first study carried out to investigate the behaviour of HIF-1 alpha gene transcripts during hypoxia in representative of marine hypoxia-sensitive fish species.

Astaxanthin is one of the major carotenoids in aquatic animals including salmonid fishes and is the preferred pigments added to salmon feed. It's also a powerful antioxidant compared to other carotenoids and that may confer numerous health benefits. The aim of the present experiment was to investigate the effect of Astaxanthin deposition on the lipids peroxidation by studying the Malondialdeide (MDA) level in muscle of rainbow trout (Oncorhynchus mykiss). The Astaxanthin concentrations in fish fed with a commercial sources as Lucantin (R) Pink (BASF Ludwigshafen, Germany) reached values to 5.76 +/- 0.18x10(-3) mg/g after 50 days feeding, while the MDA concentration decreased from 1.56x10(3) to 0.45x10(3)ng/g. The correlation between MDA and Astaxanthin concentrations decreased linearly and confirmed the antioxidant properties of the pigment by reducing the lipids peroxidation.