Aquaculture Nutrition

Phospholipids (PL) are widely used as aquafeed to enhance aquaculture production, particularly in crustaceans. The most common source of PL for aquaculture is lecithin, which is derived from both animals (e.g., eggs) and plants (e.g., soybeans). Including optimal levels of PL in crustacean diets enhances growth performance, survivability, antioxidant capacity, and lipid metabolism. PL is especially critical for early juveniles, as it supports osmoregulation by elevating Na+/K+‐ATPase (NKA) activity. Furthermore, PL‐enriched diets trigger energy metabolism, enhancing their physiological performance. In reproduction, PL provides energy for lipids mobilization and steroid transformation, improving the process of vitellogenesis in females. However, excessive PL can negatively affect the survival rate (SR), molting frequency (MF), condition factor (CF), and hepatosomatic index (HSI). This comprehensive review explores recent findings on how PL‐enriched diets affect crustacean growth, metabolism, immunity, reproduction, gut microbiota, and osmoregulation. It also addresses gaps in our understanding of specific PL dietary needs for optimal crustacean health and productivity, offering evidence‐based guidelines for effective PL supplementation in aquaculture.

This study investigated the effects of astaxanthin (Ax) on the growth, body color, and immunity of Macrobrachium rosenbergii . Four different concentrations of Ax (0, 50, 100, and 200 mg kg ⁻¹ ) were supplemented in the basal diet to assess their impact on the growth, coloration, immunity, and antioxidant capacity in M. rosenbergii . After 10 and 20 weeks of feeding, compared to the control group, the addition of 100 mg kg⁻ ¹ of Ax significantly increased the weight gain rate (WGR) and specific growth rate (SGR; p < 0.05) and shortened the molting cycle ( p < 0.05). Addition of Ax increased the redness ( value) and yellowness ( value) of live and cooked M. rosenbergii ( p < 0.05), and the muscle Ax content increased as the amount of added Ax increased. The enzyme activity results showed that after 20 weeks of feeding, the inclusion of 200 mg kg ⁻¹ of Ax significantly increased the activities of superoxide dismutase (SOD) and alkaline phosphatase (AKP) in M. rosenbergii ( p < 0.05) and significantly decreased the activity of malondialdehyde (MDA; p < 0.05). Compared with control group, the addition of 100 mg kg ⁻¹ of Ax significantly increased the expression levels of genes related to immunity and antioxidant activity ( p < 0.05). Additionally, there were significant differences in the expression levels of molting‐related genes (ecdysteroid receptor ( EcR ) and retinoid X receptor ( RXR )), across the different Ax supplementation levels and molting stages. Considering all factors, the addition of 100 mg kg ⁻¹ of Ax to the feed not only improved the growth performance and body color of M. rosenbergii but also enhanced its immune and antioxidant capabilities. This study provides a reference for the application of Ax in crustacean feed.

Zinc (Zn) is a kind of critical mineral element for aquaculture and play an important role in growth performance and immunity. Hence this study was aimed to assess alterations in specific growth rate (SGR), feed utilization, activities of digestive enzymes, serum biochemical indexes, the quantity and expression of immunoglobulin M (IgM) in juvenile soft‐shelled turtle, Pelodiscus sinensis , response to dietary gradient Zn levels. Fish meal‐based diets were supplemented with 0, 10, 20, 30, 40, and 50 mg/kg Zn, the analyzed dietary Zn contents were 35.43, 46.23, 55.38, 66.74, 75.06, and 85.24 mg/kg Zn, respectively. ZnSO 4 · 7H 2 O was used as the Zn source. Turtles (weighing ~4 g) were divided into six groups and were stocked for 12 weeks. The results indicated that SGR, pepsin activity in the stomach, intestinal alpha‐amylase and lipase activities, total protein content, acid phosphatase (ACP), and alkaline phosphatase (AKP)activities, the contents and mRNA of IgM and insulin‐like growth factor‐I (IGF‐I) enhanced with dietary Zn inclusions to 55.38 or 66.74 mg/kg and then diminished with increasing Zn contents. Escalating Zn levels to 66.74 mg/kg lowered the feed conversion ratio (FCR), serum aspartate aminotransferase (AST), alanine transaminase (ALT) activities, urea nitrogen, triglyceride (TG), cholesterol, and myeloperoxidases (MPO) activity, beyond which they improved. Insufficient or extra Zn depressed the SGR, reduced the feed utilization and digestive enzyme activities, changed the biochemical indicators, and depressed the immunity. The recommended level of Zn in juvenile P. sinensis is 63.75, 61.25, and 61.20 mg/kg diet, derived from analysis of SGR, serum AST, and ALT activities.

Nile tilapia of an initial average weight of 36.55 ± 0.15 g were stocked in 15 tanks at 20 fish per tank. Five isonitrogenous and isolipidic experimental diets (31.5% crude protein, 7.45% crude lipid) were formulated to replace 0% (D‐0 diet), 25% (D‐25 diet), 50% (D‐50 diet), 75% (D‐75), and 100% (D‐100 diet) of fish meal (FM) with cottonseed meal (CSM) and blood meal (BM). After 60 days of rearing experiment, results showed that final body weight (FBW), specific growth rate (SGR), feed conversion ratio (FCR), weight gain rae (WGR), protein efficiency ratio (PER), the whole‐body crude proteins and ash content exhibited no significant change at D‐25, D‐50, and D‐75 group ( p > 0.05) compared to the control. FBW, WGR, PER, SGR, crude protein, and ash were significantly lower, while FCR was significantly higher in D‐100 compared to control ( p < 0.05). Serum biochemical activities indicated that albumin (ALB), triglycerides (TGs), and total cholesterol (TC) exhibited no significant change ( p > 0.05) among all treatments. However, glucose (GLU) concentration was significantly increased in the D‐50 and D‐75 groups compared with the control group. Meanwhile, alanine aminotransferase (ALT) was significantly lower in the D‐100 group, aspartate transaminase (AST) was significantly higher in D‐25, D‐50, D‐75, and D‐100 groups, superoxide dismutase (SOD) activity was higher in D‐75 group, and glutathione‐peroxidase (GSH‐Px) was lower in D‐25 compared to the control group. These results suggest that D‐75 is the optimal substitution level without adverse effects on GIFT tilapia juveniles.

The use of enriched rotifers with industrially produced microalgae represents a valuable tool for the enhancement of zebrafish larval nutrition and increased biological performance. Currently, a monoculture of microalgal species (Nannochloropsis sp.) in form of liquid paste is routinely used for rotifers enrichment for zebrafish larvae feeding; however, the most adequate typology (i.e., paste or freeze-dried) of the industrially produced microalgal biomass is still controversial. This work aimed to compare the effects of rotifers enriched with three different industrially produced microalgae species (i.e., Nannochloropsis oceanica, Tetraselmis chui, and Tisochrysis lutea) using paste and freeze-dried powder. Enriched rotifers were provided as feed during larval growth and the impact on growth and survival was evaluated. The use of enriched rotifers with both paste or freeze-dried microalgae improved growth compared to larvae fed exclusively with commercial microdiet. Larvae fed rotifers enriched with N. oceanica and T. chui attained higher weight and length both at 15 and 30 days postfertilization (dpf), while the use of microalgae in paste contributed to greater larvae lengths when compared to freeze-dried. The experimental results in this study revealed that N. oceanica and T. chui in paste are the most suitable microalgae forms to be used in zebrafish larvae nutrition and in the improvement of enrichment methodologies for rotifers.

This study evaluated the dietary fishmeal substitution by full-fat (FF) and defatted (DF) Zophobas morio meals regarding growth, feed efficiency, proximate and fatty acid compositions, digestive enzymes activities, histology and midgut microbiota in gilthead seabream (Sparus aurata). Juveniles initially weighing 3.4 g were distributed to triplicate groups and fed at satiation six isoni-trogenous (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 Z. morio meal at 49 g/kg (FF-49) and 97 g/kg (FF-97), and three diets contained a DF Z. morio 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 Z. morio 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 Z. morio meals. Proximate composition of fish was altered but without indicating a clear correlation with the form or inclusion level of Z. morio. Increasing inclusions of both forms of Z. morio 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 Z. morio 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 Saccharimona-dales and Rhodobacteraceae, except FF-97 fish that had high abundances of Legionella-and Pandoraea-like bacteria. To conclude, Z. morio meal, either FF or DF, is a suitable insect protein for fishmeal substitution towards more sustainable aquafeeds for S. aurata.

This study evaluates the influences of dietary mangrove ( Avicennia marina ) leaf aqueous extract (MLAE) on growth, health, and stress tolerance in Liza ramada over an 84‐day feeding assessment. Fish (initial weight: 34.89 ± 0.15 g) were served diets encompassing 0, 100, 200, 300, or 400 mg/kg MLAE. The 300 mg/kg MLAE group reached the best growth performance compared to other groups ( p < 0.05). The feed conversion ratio (FCR) was also the most productive at this level. Polynomial regression identified an optimal MLAE range of 250–275 mg/kg for maximizing growth and feed efficiency. Digestive enzyme potencies (amylase, lipase, and protease) were elevated ( p < 0.05) in the 300 and 400 mg/kg groups. Higher MLAE levels reduced total bacterial count and populations of Vibrio spp. and Escherichia coli . Histological analysis showed enhanced intestinal villi structure and immune cell infiltration in MLAE‐fed groups. Blood chemistry revealed increased total protein (TP), albumin (AB), and globulin contents and reduced cholesterol in the 200–400 mg/kg groups. MLAE improved hypoxia tolerance, indicated by increased LT50% values, and reduced stress markers (glucose, cortisol) under hypoxia. Immune indicators (lysozyme activity, bactericidal activity [BA], and NBT%) and antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx]) were enhanced, with lower malondialdehyde (MDA) levels. These outcomes suggest that MLAE supplementation enhances growth, health, and stress resilience in gray mullets, offering potential applications for sustainable aquaculture. Further studies should explore the mechanistic pathways underlying these benefits and assess the long‐term impacts of MLAE supplementation on fish health and aquaculture productivity.

The reliance on fish meal (FM) as the primary protein source in aquafeeds is becoming increasingly unsustainable due to overfishing and limited resources. Therefore, finding an alternative protein source for FM is a crucial issue in the research of aquafeed nutrition. Corn gluten meal (CGM) is a plant protein source commonly used in aquafeeds that has been considered a practical substitute for FM. This study is designed to evaluate the impacts of substituting FM with CGM in the feed of red sea bream ( Pagrus major ) on growth, feed utilization, and biochemical composition. Total of 600 juvenile (8.60 ± 0.011 g; initial mean body weight ± SE) fish were assigned to twelve 300 L flow‐through tanks. The control (Con) diet included 55% FM. In the Con diet, 20%, 40%, and 60% of FM were replaced with CGM, identified as the CG20, CG40, and CG60 diets, respectively. Four isoproteic (51.5%) and isolipidic (14.5%) diets were prepared. All diets were supplied to triplicate groups of fish. Fish were hand‐fed to satiation level twice daily for 56 days. At the completion of the 56‐day feeding trial, the weight gain (WG) and specific growth rate (SGR) of red sea bream fed the Con and CG20 diets were superior ( p < 0.0001 for both) to fish fed the CG40 and CG60 diets. WG and SGR of red sea bream linearly decreased with elevated dietary FM replacement levels ( Y = −5.003333 X + 38.9667, R ² = 0.9004, p < 0.0001 and Y = −0.002607 X + 0.0314, R ² = 0.9083, p < 0.0001, respectively). Feed consumption (FC), protein efficiency ratio (PER), and protein retention (PR) of red sea bream fed the Con and CG20 diets were statistically ( p < 0.006, p < 0.003, and p < 0.004, respectively) higher than those of fish fed the CG40 and CG60 diets. The feed conversion ratio (FCR) of red sea bream fed the CG40 and CG60 diets were statistically ( p < 0.0002) higher than that of fish fed the Con and CG20 diets. The hepatosomatic index (HSI) of fish fed the Con and CG20 diets was statistically ( p < 0.005) lower than that of fish fed the CG40 and CG60 diets. Neither the plasma and serum parameters nor the biochemical composition except for arginine and lysine content of the whole‐body fish were statistically ( p > 0.05) altered by dietary FM substitution with CGM. In conclusion, FM up to 20% could be replaced by CGM in the diet of red sea bream without bringing about negative impacts on the growth, feed utilization, biological indices (except for HSI), blood chemistry, proximate composition, amino acid (AA; except for arginine and lysine content), and fatty acid (FA) profiles.

The present study investigated growth performance, body composition, hepatic and intestinal morphology, biochemical indices, transcriptomic responses, and metabolomic profiles in giant freshwater prawn ( Macrobrachium rosenbergii ) fed six kinds of soy protein concentrate (SPC) diets over an 8‐week feeding trial. The six SPC diets were formulated by replacing varying proportions of fishmeal (FM) with SPC, with the final percentage of FM set at 350, 280, 210, 140, 70, and 0 g/kg, respectively, and designated as F35, F28, F21, F14, F7, and F0 diets. Results showed that the final body weight (FBW), weight gain, and specific growth rate (SGR) of prawn fed F35 were greater than those of prawn fed F7 and F0. The crude lipid content of prawn fed F0 was higher than that of prawn fed F28. Notably, increasing SPC substitution levels disrupted hepatopancreas morphology, with structural degradation becoming more pronounced beyond 40% replacement (F21). Compared to F35 group, the F0 significantly decreased the activity of glutathione peroxidase (GSH‐PX), and increases the content of malondialdehyde (MDA) and nitric oxide (NO) in hemolymph. Based on the transcriptomics, two differentially expressed genes (DEGs) LOC136825138 and LOC136856310 were consistently observed across all groups. The metabolomics indicated that 77 differentially expressed metabolites (DEMs) across all treatments. A negative correlation was observed between LOC136856310 and eicosapentaenoic acid (EPA), arachidonoyl dopamine, 8Z,11Z‐eicosadienoic acid, and vitamin E nicotinate. A comprehensive analysis of both metabolomic and transcriptomic data sets revealed substantial perturbations associated with “alpha‐linolenic acid metabolism” and “glycerophospholipid metabolism”. In conclusion, elevated levels of dietary SPC had detrimental effects on the growth performance, hepatopancreas health, antioxidant capacity, and immune function of M. rosenbergii . Based on the growth performance, dietary FM level for M. rosenbergii could be reduced to 140 g/kg by using SPC as a sole substitute, with an inclusion of 211 g/kg of SPC in the diet.

Understanding the mechanisms of nutrient regulation in bivalves is crucial for optimizing their growth under varying dietary conditions. In the present work, juveniles of the carpet shell clam ( Ruditapes decussatus ) from the same cohort were size‐segregated to obtain fast and slow growing phenotypes. These clams were then conditioned to diets presenting a range of lipid/carbohydrate proportions but similar carbon:nitrogen (C:N) ratios. Subsequently, experiments were conducted to determine elemental (C and N) balances in order to achieve the following aims: (a) To identify strategies of homeostatic nutrient regulation in relation to either endogenous (growth phenotype) or dietary factors and (b) to quantify the extent to which stoichiometric adjustments (at both pre‐ and postabsorptive levels) are accomplished throughout the successive components of elemental balances. The elemental balances of both C and N exhibited higher values under the lipid‐rich diets, indicating the presence of nutritional limitations in juvenile clams fed on low lipid/carbohydrate proportion, resulting from a greater digestive imbalance of lipids in diets of low digestibility coupled to limited dietary lipid income. These nutritional limitations were more effectively managed by the fast‐growing phenotype, pointing to the importance of enhanced energetic status in sustaining homeostatic nutrient regulation. The stoichiometric coupling between consumed diets and the biosynthetic requirements of growing tissues relied on postabsorptive rather than preabsorptive mechanisms, although notable discrepancies in this regard were observed between conditioning diets.

Unreasonable ratio of protein to lipid in feeds could affect growth, antioxidant, and related pathway genes expression. This study aimed to investigate the suitable proportion of protein to lipid in feed with Parabramis pekinensis . The ratio protein‐lipid ( P / L) indicated by G1 (2.52), G2 (3.16), G3 (4.03), G4 (5.33), G5 (7.49), and G6 (11.67), which were fed to P. pekinensis (80 ± 10.52 g) for 56 days. The present results showed that diets with a protein‐to‐lipid ratio of approximately 3.5:1 (35% protein and 10% lipid, or less) were optimal for enhancing growth parameters, including body weight, WGR, PER, VSI, HSI, SGR, and feed conversion ratio (FCR). The quadratic regression analysis of FCR and protein efficiency ratio (PER) in P. pekinensis showed that P/L ratio performed best around 5.33. As the P/L ratio in feeds turned down, the best growth performance appeared at about 5.33 ( p < 0.05), which was due to the unbalanced feed protein and fat levels. Meanwhile, P/L in 5.33 group exerted a protective function against oxidative damage in P. pekinensis . In addition, the increased antioxidant capacity contributed to the growth performance of the fish in 5.33 group, which showed the connection obviously. Thus, the connection existed in target of rapamycin (TOR) and Nrf2 signaling pathway, which was downregulated when the P/L ratio was around 2.52 and 11.67. On the contrary, the P/L ratio around 5.33 could enhance the expression of tor and s6k1 to improve the growth of P. pekinensis . In the Nrf2 signaling pathway, the expression of keap1 , sod1 , and gpx affected antioxidant ability and the P/L ratio from 4.03 to 7.49 could be able to balance the antioxidant capacity, maintaining in normal level of P. pekinensis .

With the increasing prevalence of high‐fat diets (HFD) in aquaculture practices, the detrimental effects of HFD on farmed fish have garnered significant attention. Creatine has emerged as a promising green feed additive for aquaculture species; however, its potential role in mitigating the negative impacts of HFD remains poorly understood. To address this knowledge gap, the present study was designed to investigate the protective effects of dietary creatine supplementation on HFD‐induced hepatic lipid metabolism disorders and muscle quality deterioration in juvenile grass carp ( Ctenopharyngodon idella ). Three experimental diets were formulated: a control diet (5.20% lipid, control), a HFD (8.11% lipid, HFD), and a HFD supplemented with 2% creatine (HFD + creatine). Juvenile grass carp (initial weight: 4.12 ± 0.02 g) were randomly allocated into nine 300‐L indoor tanks and fed the experimental diets for 8 weeks. The key findings of this study revealed that (1) Dietary creatine supplementation significantly ameliorated the adverse effects of HFD on growth performance and feed utilization efficiency in juvenile grass carp. (2) Creatine supplementation improved muscle quality parameters in juvenile grass carp. (3) Dietary creatine attenuated HFD‐induced hepatic lipid accumulation through enhanced fatty acid β ‐oxidation, which was mediated by mfn2‐dependent mitochondrial fusion. Notably, this study elucidates a novel molecular mechanism whereby creatine activates mitochondrial fusion through the binding of pparα transcription factor to specific sites on the mitofusin 2 (Mfn2) gene promoter. To our knowledge, this is the first comprehensive investigation from a multi‐organ/tissue perspective combined with mitochondrial dynamics analysis, providing valuable insights for developing effective nutritional strategies to counteract HFD‐induced adverse effects in farmed fish through creatine supplementation.

Black soldier fly larvae (BSFL) meal is a promising sustainable protein source for aquafeeds. Processing BSFL into meal and oil can be based on wet rendering technology where the raw material is heat treated and mechanically separated into press cake, stickwater (SW), and oil. In this study, to verify the effect of SW reincorporation into the press cake, dried BSFL cake and SW meal were included in feed mixes before extrusion. Four experimental feeds were prepared, containing 100 g kg⁻¹ BSFL meal with a cake/SW ratio of 100/0, 90/10, 80/20 and 60/40 g kg⁻¹, respectively and compared to a control feed in a trial with Atlantic salmon parr reared in freshwater. The feeds had similar nutritional value and all feeds were highly digestible. The highest content of manganese (Mn) was found in the BSFL cake feed (120 mgkg⁻¹), was reduced with increased SW inclusion and lowest in the control feed. There were no dietary differences in growth or welfare with increased SW inclusion, and no negative impact of high dietary Mn levels. The high Mn content was not accumulated in the fish, and only resulted in an increased excretion of Mn. Further studies are needed to verify these results in Atlantic salmon postsmolt.

Chum salmon (Oncorhynchus keta) is an indigenous salmonid species found in Korea. This experiment was conducted to evaluate the effects of fish meal (FM) replacement with krill meal (KM), soy protein concentrate (SPC), meat meal (MM), and chicken byproduct meal (CBM) in chum salmon diets. A control diet was designed to contain 60% FM, 5% KM, and 8% SPC (FM60). Three diets were formulated to contain 45%, 30%, and 15% FM (FM45, FM30, and FM15). The reduced protein levels after FM replacement were supplied with a mixture of KM, SPC, MM, and CBM. Fish, averaging 5.94 ± 0.19 g, were fed four experimental diets or a commercial diet (COMF) for 6 weeks. Final body weight of fish fed FM30 and FM15 diets were significantly increased than fish fed COMF. Feed intake (FI) was significantly higher in FM60, FM45, and FM30 groups than COMF group. Condition factor (CF) was significantly higher in FM15 group compared to FM60 and COMF groups. Muscle saturated, highly unsaturated, and omega-3 fatty acids were significantly higher in COMF group compared to those of fish fed other diets. FM15 groups exhibited significantly lower EPA and DHA levels compared to FM60, FM45, and FM30 groups and significantly higher omega-6 levels compared to other groups. The results indicate that a mixture of KM, SPC, MM, and CBM can be used to replace FM in chum salmon diet down to 30%–15% while maintaining normal performance compared to diet containing 60% FM.

Compared with mammals, fish have a limited capability to utilize carbohydrates, thus generally suffering from metabolic disorders when offered carbohydrate‐enriched diets. As a synthetic liposoluble derivative of vitamin B 1 , benfotiamine can alleviate the carbohydrate overload‐induced mitochondrial dysfunction in fish, but the potential mechanisms have not been well explored. The present research was performed to unveil the molecular pathways through which benfotiamine benefits the mitochondrial function of a carp species Megalobrama amblycephala , which often exhibits metabolic disturbances. First, a control (C, 30% carbohydrate) group, a high‐carbohydrate (HC, 43% carbohydrate) group, and a HC incorporating benfotiamine (1.425 mg/kg) group were conducted, respectively, in a 12‐week feeding trial. Then, two in vitro studies were performed by using primary hepatocytes. In the first one, a media treatment, a high‐glucose (HG) treatment, and a HG incorporating benfotiamine were designated, respectively. In the second one, a media group, a vehicle group, a HG group, and a HG + BL‐918 (the agonist of UNC‐51‐like kinase 1 [ULK1]) group were adopted, respectively. The results indicated that HC/HG treatment resulted in mitophagy disorder by downregulating the phosphorylation of AMPK and ULK1 and the contents of proteins involved in the PTEN‐induced putative kinase protein 1 (PINK1)‐Parkin pathway. Mitochondrial dysfunction was also observed, as was indicative of the reduced activities of mitochondrial complex I, III, and SDH. However, benfotiamine treatment increased the contents of P‐AMPK, P‐ULK1, and the PINK1‐Parkin pathway‐related proteins as well as mitochondrial complex activities. In conclusion, benfotiamine could trigger the ULK1‐mediated mitophagy to ameliorate the carbohydrate overload‐induced mitochondrial dysfunction in fish.

This study evaluated the effects of a commercial probiotic containing Arthrobacter nicotianae and Bacillus cereus on the growth performance, intestinal histological structure, body composition, hematology, and microbiota of red tilapia. Fingerlings were fed four different diets: a control diet (Pd0) and three diets (Pd1, Pd2, and Pd3) containing 15, 20, and 40 mL of probiotics/kg, respectively, for 12 weeks. Probiotic supplementation had no significant effect on water quality parameters. Compared with the control diet, all the probiotic diets improved growth performance, with greater final body weight (FBW), net weight gain (NWG), weight gain, average daily weight gain (ADWG), specific growth rate (SGR), and feed conversion efficiency (FCE). The feed conversion ratio (FCR) was lower in all probiotic-treated fish compared to control. The survival rate was also higher in the probiotic groups, though the difference was not significant. There was no significant difference in crude ash or lipid contents. However, protein content was significantly higher in Pd2 and Pd3, while moisture content (MC) was significantly higher in Pd3 than in the control group. Histological examination revealed increased villi length and width, being significantly higher in Pd2 and Pd3, while significantly greater muscular thickness and intestinal diameter were observed in Pd3-treated fish. These values increased with probiotic dose. The intestinal total viable count (TVC) was the highest in Pd2 and the lowest in the control group. The water TVC was the highest in Pd3 and the lowest in Pd0. The number of Bacillus spp. in the intestine and culture water increased with probiotic dose, while intestinal and culture water Vibrio counts decreased. Hematological analysis showed significant increases in red blood cell (RBC) count, hematocrit, mean corpuscular hemoglobin concentration (MCHC), and hemoglobin (Hb) in the treated groups compared with the control. The incorporation of A. nicotianae and B. cereus at 40 mL/kg in red tilapia diets improved growth performance, intestinal health, and general welfare.

Taste perception is essential for animals to detect nutrients, providing critical dietary information necessary for growth and survival. Since the early growth performance of alevin rainbow trout (Oncorhynchus mykiss) can be affected by food intake influenced by terrestrial ingredients without fish meal and fish oil, our study aimed to evaluate the role of taste receptors in nutrient detection and the associated signaling pathways leading to central nervous system activation in the regulation of feeding behavior. We conducted a nutritional experiment from the first feeding to 30 days, comparing the performance of fish fed a commercial-like diet (C diet: a blend of fish meal, fish oil, and plant ingredients) with those on a totally plant-based diet (V diet). After 5 and 30 days of feeding, fish were fasted for 16 h and then fed either the C or V diet, with sampling conducted at 20 min and 6 h post-meal. We evaluated the expression of nutrient-sensing genes related to fatty acids, amino acids, and sweetness, and taste receptor genes for flavors. Additionally, we examined calcium signaling pathways in the tongue, focusing on indolamine and catecholamine pathways, alongside appetite-regulating neuropeptides in the brain and intestinal hormones in the gut of alevins. Results indicated that fish on the V diet experienced a decrease in body weight gain starting 10 days after feeding to 30 days, along with changes in feed intake during the periods of 0–10 days and 21–30 days after the first meal. In tongue tissue, after 5 days of feeding, fish on the C diet showed a slight upregulation of nutrient taste receptors, but not those related to flavor, along with an upregulation of the calcium signaling pathway. By 30 days, there was a general upregulation of nutrient and flavor taste receptors, although the calcium signaling pathway showed less clear evidence of regulation. A significant dysregulation of the serotonin pathway, along with its degradation, was observed in the tongues of fish fed the V diet at both 5 and 30 days. For the first time in fish, catecholamine quantification levels in the tongue emerged as a potential marker for nutrient detection, with high quantification of L-DOPA after 5 days on the V diet, but much lower after 30 days. This impaired monoamine and catecholamine turnover in the tongue could be linked to a failure in activating the tongue-brain axis, potentially contributing to reduced food intake, as indicated by poorly regulated brain neuropeptides but also intestinal hormones in fish fed the V diet after 30 days. Overall, these findings demonstrate that the V diet disrupts the feeding response at an early stage, underscoring the heightened sensitivity of rainbow trout alevins’ tongue sensing systems to novel food sources during critical early development.

Feeding habits and dietary preferences of wels catfish (Silurus glanis) were investigated in Sıddıklı Dam Lake through the examination of 200 individuals. The results revealed that the species predominantly exhibited piscivorous feeding characteristics, with Tinca tinca (IRI% = 78.93) identified as the primary food source. The food items in the stomach showed a wide spectrum, ranging from benthic invertebrates, crustaceans, molluscs, amphibians, and mammals to fishes. The study not only assessed the general food composition of wels catfish but also delved into the seasonal variations in diet composition. It was found that the stomach fullness index (FI) varied significantly among the seasons, with Winter showing the highest values (0.827). On the other hand, the lowest value was detected in the Autumn season (0.480). Age and length groups were also considered, with notable differences in stomach FI and diet composition observed across different stages of growth. Food preference analysis highlighted the selective tendencies of wels catfish towards certain food types, with Atherina boyeri and T. tinca emerging as preferred choices in different size groups. For small, medium, and large length individuals, the most preferred prey fish were A. boyeri (Va = 0.39518, χ2 = 31.2336), T. tinca (Va = 0.63564, χ2 = 82.8073) and T. tinca (Va = 0.666495, χ2 = 88.4307), respectively. The findings provide valuable insights into the feeding behaviour of wels catfish, underscoring the importance of understanding these patterns for effective management and conservation efforts. Further research should aim to explore the ecological implications of these feeding habits on the overall aquatic ecosystem.

An 8‐week breeding experiment was conducted to study the impacts of adding different levels (0%, 3.1%, 6.2%, 9.3%, 12.4%, and 15.5%) of hydrolyzed feather meal (HFM) in place of fish meal (FM) in the feed on the growth performance, immune function, and antioxidative ability of juvenile largemouth bass ( Micropterus salmoides ), with fishmeal substitution levels (FSLs) of 0% (control group; FSL0), 10% (FSL10), 20% (FSL20), 30% (FSL30), 40% (FSL40), and 50% (FSL50), respectively. The findings show that there were no notable differences observed among the different treatment groups when contrasted with FSL0. However, as the substitution level increased, final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) declined, while the feedback coefficient rate (FCR), condition factor (CF), hepatosomatic index (HSI), and viscerosomatic index (VSI) increased. With an increase in the FSL, catalase (CAT) activity increased in all the groups and was significantly higher in the FSL20 and FSL50 groups than the control group; SOD activities in FSL40 and FSL50 significantly increased, and the plasma MDA contents in FSL40 and FSL50 significantly decreased. The gene expression levels of IL‐10 and IL‐8 in the groups FSL20 to FSL50 significantly decreased. When compared with FSL0 , the gene expression levels of CHOP and ATF6 were also significantly lower in the FSL10 to FSL50 groups. The overall expression level of ASK1 was significantly reduced in the FSL20 group. Similarly, the expression level of JNK1 was also significantly reduced in the FSL20 group. To sum up, replacing FM with HFM at 50% did not impact the growth of juvenile largemouth bass. An FSL range of 20%–50% can enhance the antioxidant capacity of largemouth bass, reduce inflammation and stress states, and have beneficial effects on the body. It is beneficial for maintaining the healthy growth of largemouth bass.

Food-derived bioactive peptides could serve as feed ingredients and/or feed additives. We investigated the health-promoting properties of low molecular weight duck blood protein hydrolysate (DBPH), fractionated by ultrafiltration with a 10 kDa molecular weight cut-off membrane, in flowerhorn fish. The analysis of molecular weight distribution revealed that the most common sizes of DBPH fell within the range of 3–7 kDa (39.68%), followed by >7–10 kDa (20.69%), 1–3 kDa (23.03%), and <1 kDa (9.00%). After 1 month of the feeding trial, fish fed with diets supplemented with 2% DBPH exhibited the highest growth, antioxidant activity, and humoral immune response enhancement under normal conditions. In addition, microbiome analysis confirmed that 2% DBPH possesses antimicrobial activity, as evidenced by the significant decrease in operational taxonomic units (OTUs) and alpha diversity indexes, including Chao1 and Shannon. Compared to the control group, fish that were fed with diets supplemented with 2% DBPH exhibited a significantly higher abundance of the genera Cetobacterium and Romboutsia, which could serve as indicators of the overall health and well-being of the fish. After a Streptococcus agalactiae challenge, fish fed with diets supplemented with 2% DBPH exhibited an enhanced ability to modulate inflammatory genes, including interleukin (IL)-1β, IL-6, CC, and CXC chemokine as well as antioxidant gene expression (superoxide dismutase (SOD) and catalase (CAT)). Overall, dietary supplementation with 2% DBPH could improve the overall health of the flowerhorn fish by ameliorating humoral immune response, alleviating oxidative stress, and strengthening resistance against S. agalactiae.

Metabolic disorders and complications induced by high‐fat diets (HFDs) are a hot research topic in aquatic animal nutrition and health, but the mechanism of gut microbes and their metabolites on muscle homeostasis is not yet clear. In this study, a 16‐week HFD (Con, 6% fat and HFD, 12% fat) rearing experiment was conducted with a freshwater drum (20.88 ± 2.75 g, about 20,000 fish per pond) to investigate the underlying regulation of gut microbes on muscle nutrient and metabolism. Results revealed that HFD had no remarkable effect on proximate nutrients (moisture, ash, crude protein, and crude fat), total amino acids, and fatty acids contents in muscle. Moreover, decreased acetic acid content by HFD in the gut and muscle was confirmed to regulate lipid metabolism, as evidenced by the activation of fatty acid synthesis (acetyl‐CoA carboxylase alpha [ACC1] and sterol regulatory element binding protein‐1 [SREBP1]) and inhibition of fatty acid lipolysis (AMP‐activated protein kinase [AMPK], adipose triglyceride lipase [ATGL], and carnitine palmitoyl transferase 2 [CPT2]). Interestingly, RNA‐seq revealed glycolytic metabolism (glycolysis/gluconeogenesis and pyruvate metabolism) was active in the muscle under HFD, which was further confirmed to be the intermediate for acetic acid to regulate lipid metabolism. Strikingly, gut microbe Rikenellaceae_RC9_gut_group and Knoellia regulate muscle lipid and glucose metabolism through their derived metabolite acetic acid, which is the key target for gut microbe to regulate muscle. Taken together, these results reveal the regulatory mechanism of gut microbes and derived metabolites on muscle metabolism and development, providing a theoretical basis for the healthy regulation of HFD in aquatic animals.

Some coral species in natural reef systems derive benefits from fish which live in close association with them. This study investigates the benefits of incorporating fish in ex situ coral culture to enhance coral physiological performance. Corals that typically have fish associations ( Acropora kenti and Pocillopora verrucosa ) and those that do not ( Porites lutea and Platygyra daedalea ) were grown in aquaria under different fish‐associated treatments for 3 months. Physiological performance of the corals, including growth, protein content, symbiont density and photosynthetic efficiency were assessed in the different treatments where corals were (1) kept with a school of Chromis viridis fed a pelleted diet, (2) supplied filtered water from a tank housing C. viridis , (3) fed live feeds whilst maintained with C. viridis , (4) supplied only with live feeds, (5) supplied with a pelleted fish diet without C. viridis and (6) not supplied feeds and without C. viridis . Whilst the responses of the corals varied between species, generally, exposure to fish or fish‐water increased the protein and/or symbiont density within coral tissue. A. kenti and P. lutea , which derive a higher proportion of their energy requirement from autotrophy, displayed improved growth in the fish treatments, whilst the more heterotrophic P. verrucosa grew fastest when supplied with live feeds. The more heterotrophic, slow‐growing P. daedalea did not show significant improvements in growth under any of the treatments, and there were no major differences in photosynthetic efficiency between treatments in any of the corals. These results indicate that incorporating fish into coral culture could provide an accessible source of nitrogen and phosphorous enrichment via the dissolved portion of the fish’s wastes and, in turn, enhance the growth of corals more reliant on autotrophy, like Acroporids. The results point to potential efficiency gains for coral husbandry practices, with the aim of satisfying the growing demands of reef restoration and ornamental aquaculture.

Guanidinoacetic acid (GAA)—a nutritional additive—is essential for the healthy growth of aquatic animals. The experiment was conducted to examine the effects of dietary GAA on growth, muscle amino acid composition, antioxidative indices, and nonspecific immunity for juvenile Litopenaeus vannamei. Total 800 healthy shrimp (initial mean weight = 0.27 ± 0.03 g) were equally distributed into 15 tanks (0.3 m³; five groups, and three repeats per group) and fed with diets containing GAA levels (e.g., 0, 0.04%, 0.10%, 0.13%, and 0.16%, named G0, G004, G010, G013, and G016, respectively) for 8 weeks (four times a day). At the end of the trial, shrimps from all replicate groups were weighed, and serum, hepatopancreas, and muscle were collected from three random tails. The weight gain rate (WGR) and specific growth rate (SGR) were significantly higher, and feed conversion rate (FCR) was significantly lower in G010 and G013 groups than in G0 group. No significant effect of GAA on the total amino acids of each treatment was observed. Serum superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) were significantly higher, and malondialdehyde (MDA) levels were significantly lower in G010, G013, and G016 groups compared to G0 group. Alkaline phosphatase (AKP), phenoloxidase (PO), lysozyme (LZM), and acid phosphatase (ACP) activities were significantly higher in G010, G013, and G016 groups than in G0 group. The mRNA expressions of immune deficiency (imd) and lzm genes in G010 and G013 groups were significantly upregulated. Following the challenge with Vibrio harveyi, the overall percent mortality of shrimp showed a gradually decreasing trend with the increase of GAA supplementary but was not significantly different from each other. In conclusion, GAA can improve the growth, antioxidant ability, and nonspecific immunity for L. vannamei.

Soybean meal (SBM) is commonly used in aquafeeds due to its wide availability, reasonable protein content, and cost-effectiveness. However, high SBM inclusion levels in the diets of carnivorous fish, such as Atlantic salmon (Salmo salar), can cause soybean meal-induced enteritis (SBMIE), resulting in compromised gut health, reduced nutrient absorption, and impaired growth. An 8-week study was conducted to evaluate the potential of brewers’ yeast-derived functional feed additives (FFAs), specifically yeast cell wall β-glucans (PβG [purified β-glucan]) and yeast cytosolic extracts (YEs), to mitigate the adverse effects of SBMIE in Atlantic salmon parr. Fish were fed diets containing 30% SBM (30-SBM) with either 0.02% β-glucan (30-SBM+PβG) or YE at 1% (30-SBM+YE1) and 2.5% (30-SBM+YE2.5) inclusion levels and compared against a control diet without SBM (0-SBM). The study assessed growth performance, haematological parameters, distal intestinal morphology, and the distal intestinal gene expression levels of enteritis biomarkers (casp3b, pcna, and hsp70). The results showed that PβG and 1% YE supplementation significantly reduced the severity of SBMIE, with improvements in intestinal morphology, including reduced intraepithelial leukocytes (IELs) levels and goblet cell hyperplasia. Intestinal gene expression levels of casp3b and pcna were significantly downregulated in the PβG and YE fed fish relative to the 30-SBM fed fish, indicating reduced apoptosis and more controlled cell proliferation. However, the effects of 2.5% YE supplementation were less pronounced, indicating a dose-dependent response. These findings demonstrate that both PβG and YE from 100% Saccharomyces cerevisiae can alleviate SBMIE in juvenile Atlantic salmon by supporting gut health and modulating cellular recovery processes.

Achillea wilhelmsii (AW), a plant rich in flavonoids, including lutein, apigenin, rutin, and phenolic compounds with antioxidant, antibacterial, and antifungal properties, is used in traditional medicine. In this study, the impact of AW extract on the growth, immune response, and biochemical indices of rainbow trout ( Oncorhynchus mykiss ) was investigated. Over 8 weeks, fish were fed diets supplemented with varying concentrations of AW extract (0%, 0.5%, 1%, or 2%). No significant differences were observed in growth performance, glucose levels, or key enzymes such as lactic acid dehydrogenase, alanine transaminase, or aspartate aminotransferase (AST) between the AW‐supplemented groups and the control group. However, fish that received AW supplementation showed significantly higher levels of total serum protein, lysozyme activity, superoxide dismutase (SOD) activity, and immunoglobulin M (IgM). Moreover, the AW‐fed groups exhibited lower mortality after exposure to Yersinia ruckeri . In conclusion, AW supplementation could enhance immune function in rainbow trout and decrease mortality after exposure to Y. ruckeri . Therefore, using this plant (1% and 2%) in aquaculture could be justified as a means to increase resistance to pathogens and improve the immune system performance of fish.