Aquaculture Nutrition

Biofloc technology (BFT) is a relatively new microbial-based cultivation system that can be adopted to accomplish more sustainable aquaculture and circularity goals. This review explores aspects of BFT integrating the utilization of probiotics and phytobiotics as dietary and water supplements. This scientific-based snapshot unpacks some physiological pathways and brings a literature review on how these supplements can boost water quality, as well as aquatic species’ growth, health, and survival. Probiotics, live microorganisms that confer health benefits on the host when administered in adequate dosage, are noted for their ability to bolster animal defenses and sustain water quality in farming conditions. Recent studies showcased that selected bacteria, yeast, and fungi, once added into biofloc-based systems can enhance animal performance, act as a tool for water quality management and protect fish and crustaceans against diseases. On the other hand, phytobiotics are additives sourced from plants that normally are added into compounded feeds and are known for their health and growth benefits in aquatic animals. These additives contain plant-based substances/extracts that play a key role to suppress inflammation, pathogens, and can also act as antioxidants. These selected ingredients can promote healthy gut microbiota, improve feed efficiency, and turn on genes responsible for immunity improving disease resistance of fish/shrimp. According to this review, the adoption of probiotics and phytobiotics in BFT can greatly increase farm outputs by producing healthier animals, as well as promoting growth and consistent yields. Lastly, this review showcases the importance of proper section of probiotics and phytobiotics in order to achieve a functioning BFT. Despite its numerous advantages, BFT faces several challenges, especially related to microbial management. Probiotics and phytobiotics are practical tools that can play a crucial role to obtain a more stable environment with a desirable microbial population in water and gut. Future directions in the field should focus on optimizing the utilization of these supplements for a more resilient and sustainable BFT aquaculture.

Introduction: The use of glyphosate (Gly) has caused unnecessary economic losses to the aquaculture industry, but research on the effect of Gly on Eriocheir sinensis is very limited. The aim of this study is to reduce the negative effects of Gly, reduce yield loss, and improve economic benefits through nutritional feed control technology. Methods: The experiment involved 80 crabs randomly divided into four groups: control group, Gly group (48.945 mg/L), microbe-derived antioxidant (MA) group, and Gly and MA treatment group. The study lasted for 7 days. In this study, the effects of Gly on the digestive function of E. sinensis were investigated using histology and spectrophotometer, and the gut microorganisms of E. sinensis were analyzed using high-throughput sequencing technology. Results: The study found that exposure to Gly resulted in separation of the folds of the midgut mucosa of Eriocheir sinensis from the basement membrane, a decrease in the fold area of the hindgut mucosa, and an increase in the number of B cells in hepatic tubules. Additionally, the lipase activity of the intestine in the Gly group was significantly higher than that of the control group and the MA + Gly group, while the hepatopancreatic lipase decreased significantly. The amylase activity in the intestine and hepatopancreas of the Gly group was significantly lower than that of the control group. The trypsin activity in the hepatopancreas of the MA + Gly group was significantly higher than that of the Gly group. The Shannon diversity index in MA + Gly group was significantly lower than that in control group. At the phylum level, the abundance of the Campilobacterota in the MA + Gly group decreased. At the genus level, the proportion of the Citrobacter and Flavobacterium in the MA + Gly group decreased. Conclusion: Gly has certain effects on the digestive tissue function, intestinal microbial diversity index and intestinal microbiota structure of E. sinensis, and MA can ameliorate the negative effects of Gly on E. sinensis.

In recent years, zinc oxide nanoparticles (ZnO NPs) have gained attention as feed additives due to their high bioavailability. However, research on their impact on fish growth and health is limited. To investigate the influences of dietary addition of ZnO NPs on growth performance and immune function of rare minnow, rare minnows were fed diets with different ZnO NPs content. Growth analysis showed that ZnO NPs had a negative effect on the weight of rare minnow, decreasing and then increasing condition factors (CFs) and specific growth rate. Additionally, the accumulated zinc (Zn) level was significantly higher (p <0.05), and the liver injury index was significantly higher (p <0.05) in the dietary ZnO NPs group compared to the control group. The number of erythrocytes and leukocytes in blood samples increased and then decreased after treatment with ZnO NPs. It was further found that ZnO NPs as a dietary supplement significantly increased the Zn content and markedly repressed the expression of growth-related genes after 60 days of accumulation in muscle tissues, and accumulation in liver tissues for 60 days significantly enhanced the expression of immune modulation–related genes expression (p<0.05). The findings suggested that short-term supplementation of ZnO NPs could positively affect fish growth and immune function. However, prolonged supplementation of dietary ZnO NPs resulted in reduced body weight and compromised immune function owing to the buildup of Zn in different tissues.

The purpose of the study was to investigate the effects of astaxanthin on ovarian development of largemouth bass (Micropterus salmoides) female. Five isonitrogenous and isolipidic feeds with varying levels of astaxanthin (0.8, 19, 41, 97, and 200 mg/kg) were grouped as AS0, AS20, AS40, AS100, and AS200, respectively. The results indicated that the gonadosomatic index (GSI) was significantly greater in the AS40 and AS100 than in AS0 and AS200 (p<0.05). The AS40 and AS100 exhibited a dramatically lower hepatosomatic index (HSI) compared to the other groups (p<0.05). The content of vitellogenin (VTG) was significantly increased in AS100 compared to the AS0, AS20, and AS200 (p<0.05). Testosterone (T) levels were significantly lower in the AS200 compared to the other groups (p<0.05). The AS40, AS100, and AS200 groups exhibited significantly greater follicle-stimulating hormone (FSH) levels than the AS0 and AS20 group (p<0.05). The luteinizing hormone (LH) level was significantly higher in AS100 compared to the other groups (p<0.05). The estradiol (E2) levels were significantly higher in AS40 compared to the AS0 and AS200 groups (p<0.05). The total antioxidant capacity (T-AOC) was significantly higher in AS100 than the AS0 and AS20 groups (p<0.05). The superoxide dismutase (SOD) activity was significantly higher in AS40 compared to the AS0 and AS200 groups (p<0.05). The malondialdehyde (MDA) level was significantly decreased in AS40 than the other groups (p<0.05). Transcriptomic analysis of ovarian tissue revealed that differentially expressed genes primarily involved in pathways such as “ovarian steroidogenesis,” “steroid hormone biosynthesis,” and “arachidonic acid metabolism.” The expression of genes involved in ovarian steroidogenesis and arachidonic acid metabolism, such as cytochrome P450 family 2 subfamily J member (cyp2j), insulin-like growth factor 1 (igf1), phospholipase A2 group (pla2g), FSH receptor (fshr), and acute regulatory protein (star), was significantly upregulated in the AS40 group (p<0.05). In summary, appropriate amount of astaxanthin supplementation in the diet enhance gonadal development, antioxidant capacity, and sex hormone levels, promote the expression of genes related to gonadal development, and consequently, enhance reproductive performance of largemouth bass.

Atlantic salmon are one of the most important fish species in global aquaculture production. However, temperature increases attributed to climatic events impair the production of Atlantic salmon during summer. Additionally, the nutritional requirements for this species when reared under elevated temperatures require elucidation. To address this gap, a feeding trial was conducted to investigate the effect of glutamine supplementation—a functional amino acid (AA) important for energy production and gut health—on the growth, metabolism, gut morphology, antioxidant capacity and thermal tolerance of Atlantic salmon parr at elevated temperatures (22°C). Atlantic salmon were pair-fed three isoenergetic diets: a control diet (D1, no addition of glutamine), D2 (7% glutamine supplementation with other dietary AA levels reduced—isonitrogenous to D1) and D3 (6% glutamine and with the same AA profile as D1). Metabolic rate measurements and sampling commenced after 7.5 weeks on diets and 3 weeks of exposure to 22°C. Glutamine supplementation (D2 and D3) did not affect specific growth rate (SGR), condition factor, relative gut mass or carcass composition despite fish fed D3 having increased pyloric caeca fold height (hF). Resting, maximum and digestive metabolic rates were also unaffected by glutamine supplementation. Contrary to findings in other fish species at optimum temperatures, this study showed that glutamine supplementation did not improve the growth performance of Atlantic salmon parr at elevated temperatures despite enhancing pyloric caeca surface area.

This study evaluated the growth performance, immune response, hepatopancreatic health, and disease resistance in Litopenaeus vannamei fed diets supplemented with fermented pomegranate peel polyphenols (FPPP) for 45 days. Five diets were formulated to contain various levels of FPPP: FP0 (no FPPP), FPPP inclusion at 0.015% (FP1), 0.030% (FP2), 0.060% (FP3), and 0.120% (FP4). The results indicated there were no significant variations in weight gain rate (WGR), specific growth rate (SGR), and feed conversion rate (FCR) of shrimp in all treatment groups (p>0.05), but the survival (SR) of shrimp was significantly higher in all groups with the addition of FPPP (p<0.05). Compared with FP0 group, the contents of total protein (TP) and globulin (GLB) in serum biochemical indexes of FP3 and FP4 groups were significantly increased, and the content of blood urea nitrogen (BUN) was significantly decreased (p<0.05). Compared with FP0 group, the activities of superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (AKP), acid phosphatase (ACP), and lysozyme (LZM) in the hepatopancreas and serum of FP3 and FP4 groups were significantly increased (p<0.05). Similarly, the activities of glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and phenoloxidase (PO) in the hepatopancreas and serum of FP2 group were significantly higher than those of FP0 group (p<0.05). In addition, the content of malondialdehyde (MDA) in the hepatopancreas and serum of shrimp in FPPP-added groups was decreased (p<0.05). Compared with FP0 group, the expression levels of SOD, CAT, glutathione S-transferase (GST), LZM, prophenoloxidase (ProPO), penaeidin-3 (Pen3), Crustin, immune deficiency (Imd), Toll, and Relish genes were significantly upregulated in the hepatopancreas of shrimp in FP3 and FP4 groups (p<0.05). Additionally, increasing the addition level of FPPP resulted in a more compact hepatosomal arrangement of the shrimp’s hepatopancreas, a more visible star-shaped lumen structure, and a significantly higher number of B cells. Finally, the cumulative SR of shrimp in FPPP groups was significantly higher than that in FP0 group after 7 days of infection with Vibrio alginolyticus (p<0.05). In summary, dietary supplementation of FPPP can improve SR, immunity, and hepatopancreatic health and resistance to Vibrio alginolyticus of L. vannamei.

This research evaluated the effect of different levels of extrusion process energy during the production of wheat and sorghum-based feeds on the growth performance and digestibility of Pacific white shrimp (Litopenaeus vannamei). Process energy consisted of mechanical and thermal components, which were both modulated via varying preconditioner steam addition. Diets were formulated to be isonitrogenous (36% protein) and isolipidic (8% fat), with three levels of thermal energy (TE) input during preconditioning (high, medium, and low). All diets showed increased starch gelatinization with increased TE, with the wheat-based diets undergoing a greater degree of gelatinization than the sorghum-based diets. There were no significant differences in final biomass, weight gain, feed conversion ratio (FCR), or survival among the different treatments. However, digestibility results showed that wheat-based diets had significantly higher apparent digestibility coefficients (ADCs) for both protein and energy compared to sorghum-based diets. Overall, increased starch gelatinization that correlated with greater digestibility was observed, but this effect was reduced in the sorghum-based diets. These findings suggest that sorghum can be used as a viable alternative to wheat in shrimp feed without negatively impacting their growth performance, while also offering potential cost savings to producers.

This trial was conducted to assess the effects of different levels of dietary fish oil on growth performance, hepatic health, nonspecific immune responses, and intestinal microbial community of Amur grayling (Thymallus grubii). Five isonitrogenous diets containing 60 (6FO), 90 (9FO), 120 (12FO), 150 (15FO), and 180 g/kg (18FO) fish oil were fed to triplicate groups of 60 fish per tank for 8 weeks, respectively. The results revealed that specific growth rate (SGR) and weight gain (WG) of fish in the 15FO group were significantly greater than those in the 6FO group (p<0.05). Somatic indices and whole-body lipid levels were positively correlated with increases in dietary fish oil levels. Trypsin and lipase activities in 15FO and 18FO groups were significantly higher than those in the 6FO and 9FO groups (p<0.05). The activities of intestinal catalase (CAT) and liver superoxide dismutase (SOD), CAT, lysozyme (LZM), alkaline phosphatase (AKP), and acid phosphatase (ACP) improved significantly as the dietary lipid content increased to 185.3 g/kg and decreased thereafter (p<0.05). The lipid metabolism-related genes peroxisome proliferator-activated receptor gamma (PPARγ) and carnitine palmitoyltransferase 1A (CPT1A) were significantly downregulated and upregulated (p<0.05), respectively, in the 15FO group. Immune-related genes in the liver and intestine, such as interleukin (IL-8), were significantly upregulated in the 15FO group (p<0.05). The liver sections from 18FO group presented more numerous and larger lipid vacuoles. Both low- (6FO) and high-lipid (18FO) diets reduced the relative abundance of intestinal Lactococcus. The relative abundances of intestinal Staphylococcus and Bacillus (mainly Bacillus anthracis) increased in the low-lipid diet group and that of Pedobacter increased in the high-lipid diet group. Second-order polynomial analysis of WG and the feed conversion ratio (FCR) for varying levels of dietary lipid revealed that a range of 194.76–198.90 g/kg dietary lipid was optimal for the growth and health of Amur grayling.

Understanding the nutritional and metabolic physiology of aquatic organisms is essential for optimizing aquaculture practices and informing ecological models. We investigated the influence of dietary composition, specifically the incorporation of multienzyme extract derived from Pleoticus muelleri waste, on the growth and metabolic processes of juvenile Cherax quadricarinatus. We investigated how these dietary changes influence dietary assimilation and tissue turnover using stable isotope δ¹³C and δ¹⁵N dynamics, in both the pleon muscle and hepatopancreas. Juvenile crayfish were subjected to two isocaloric diets for a 90-day period: a control diet (diet C) and a diet supplemented with a multienzyme extract (diet E) from red shrimp waste. Despite comparable growth rates, isotopic analysis (δ¹³C and δ¹⁵N) of the pleon muscle and hepatopancreas revealed distinct metabolic patterns between both dietary treatments. The hepatopancreas exhibited accelerated isotopic turnover relative to muscle tissue, irrespective of diet, suggesting a more dynamic metabolic role. Diet E further accelerated turnover rates in both tissues, indicative of enhanced nutrient assimilation and utilization. Consistent isotopic disparities between the hepatopancreas and muscle tissues highlighted tissue-specific metabolic functions, with the hepatopancreas serving as a metabolic hub. Molting-induced shifts in isotopic patterns underscored the dynamic interplay between metabolic processes and nutrient mobilization. Isotopic equilibrium was reached earlier for δ¹³C than δ¹⁵N, with lower discrimination factors in the hepatopancreas. While δ¹³C primarily supported metabolic processes, δ¹⁵N contributed substantially to growth, especially in muscle. These findings illuminate the complex interplay of dietary composition, isotopic fractionation, and physiological regulation in C. quadricarinatus. The metabolic enhancements induced by the diet supplemented with the extract warrant further investigation to optimize nutrient utilization and growth performance in aquaculture settings.

The aim of this study was to investigate how dietary arachidonic acid (ARA) level affects growth performance and lipid metabolism in juvenile black seabream (Acanthopagrus schlegelii). A feeding trial was conducted for 8 weeks, during which the fish (0.99 ± 0.10 g) were fed six isonitrogenous and isolipidic diets with varying ARA levels of 0.1%, 0.59%, 1.04%, 1.42%, 1.94%, and 2.42%. Fish fed the diet with 1.42% ARA had significantly higher weight gain (WG) and specific growth rate (SGR) than the other groups (p<0.05), except for the ARA1.04. As the ARA level increased, the liver and muscle effectively accumulated n−6 polyunsaturated fatty acids (n−6 PUFAs; p<0.05). However, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and n−3 PUFA contents of liver and muscle significantly decreased by increasing dietary ARA level (p<0.05). Results of liver histology showed dramatically increased vacuolar fat droplets leading to hepatic fat pathological changes in fish fed diets with ARA levels of 1.94% and 2.42% (p<0.05). Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased with increasing dietary ARA level which was accompanied with elevated liver lipid content (p<0.05). Consistently, triglyceride (TG) and nonesterified fatty acid (NEFA) concentrations of serum and liver, and serum cholesterol (CHO) concentration increased (p<0.05). As the level of dietary ARA increased, the indicators of lipid metabolism such as sirtuin 1 (sirt1) and peroxisome proliferator-activated receptor α (pparα) also increased (p<0.05). However, after reaching their peak in ARA1.04 group, the level of these indicators declined (p<0.05). The same trend was observed for the expression of genes related to the downstream pathways. While the mRNA levels of sterol regulatory element–binding protein-1 (srebp-1) and its downstream genes were markedly increased with the increase of dietary ARA level (p<0.05). In conclusion, these data suggested that the optimum dietary ARA requirement of A. schlegelii is 1.03% of diet based on the WG. The study revealed that a diet containing 1.04% ARA can activate the expression levels of sirt1 and pparα leading to promoted lipolysis. However, dietary ARA levels of ≥1.42% induced lipid accumulation in the liver, as they suppressed the mRNA levels of sirt1 and pparα, while elevating the expression level of genes related to lipogenesis.

A 50-day test was adopted to compare the growth performance, liver histology, glucose metabolism, lipid (L) metabolism, ion transport, and ammonia metabolism of tilapia fed different carbohydrate–lipid (C:L) ratio diets under saline–alkaline water (salinity = 16 mmol/L and alkalinity = 35 mmol/L). The C and L levels of five isoenergetic (16.5 kJ/g) and isonitrogenous (32% protein) diets were C45%:L3% (L3), C38%:L6% (L6), C31%:L9% (L9), C24%:L12% (L12), and C17%:L15% (L15). This study found that the dietary C:L ratio did not affect the survival rate (SR), feed conversion ratio (FCR), or condition factor of tilapia in saline–alkali water, but fish in the L12 group had the highest weight gain (WG) rate and the lowest hepatosomatic index (HSI) compared with the other groups. Fish fed the higher C diet (L3 and L6) had a higher ion transport capacity and ammonia excretion capacity in gills. However, the highest mRNA expression of genes involved in glutamine metabolism and urea metabolism in the liver was found in the high-L diet groups (L12 and L15). In particular, a lower serum ammonia concentration was observed in the high-L diet groups (L12 and L15). In addition, biochemical indicators indicated that the L12 group had the highest liver pyruvic acid, lactic dehydrogenase (LDH), and lipase (LPS) and serum total cholesterol (T-CHO) contents. In summary, this study indicated that dietary Ls could promote glutamine metabolism and urea metabolism more than dietary Cs and then reduce the serum ammonia concentration of tilapia in saline–alkali water. A dietary C:L ratio of 2:1 was beneficial to the growth and ammonia excretion of tilapia in saline–alkali water in this study.

The dietary lipid level is closely associated with ovarian maturation of broodstock. However, optimal lipid requirements during broodstock gonad development for aquatic animals remain limited. In order to assess the impact of dietary lipid levels (6%, 8%, 10%, 12%, and 14% lipid, denoted as L6%, L8%, L10%, L12%, and L14%) on the ovarian maturation, antioxidant status, and messenger RNA (mRNA) expression of genes involved in the lipid metabolism of Macrobrachium rosenbergii broodstock (initial weight 10.53 ± 1.97 g), this study carried out an 8-week feeding experiment. The findings showed that while there was no significant difference in the survival rate across the groups (p>0.05), the weight gain observed in prawns fed the 8% lipid-level diet was significantly higher than those fed other diets (p<0.05). The hepatosomatic index and the gonadosomatic index showed a significant increase with the rise in dietary lipid level (p<0.05). More ovaries from M. rosenbergii broodstock reached stages Ⅲ and Ⅳ after being supplemented with dietary lipid levels between 8% and 14%. Serum glucose content did not show any significant difference among all groups (p>0.05), but serum triglyceride and total cholesterol content increased followed by a decreasing trend with increasing levels of dietary lipids, both peaking in the prawns fed a 10% lipid-level diet. Furthermore, the progesterone (PROG) and 17β-estradiol (E2) content of prawns fed the 10% and 12% lipid-level diets were significantly higher compared to other groups (p<0.05). Based on serum E2 and PROG content, the optimal lipid level needed for maximal ovarian maturation was determined to be 11.79% and 10.88%, respectively. Moreover, there were more endogenous vitellogenic oocytes in prawns fed 8% and 10% lipid-level diets, with a more compact arrangement compared to the less tightly arranged structure of the ovarian tissue in prawns fed other diets. With the increase in dietary lipid levels, there was a significant increase in the activity of superoxide dismutase. The activities of total antioxidant capacity and glutathione peroxidase initially increased and then decreased significantly, peaking at prawns fed 8% and 10% lipid-level diets, respectively (p<0.05). The malondialdehyde content reached its lowest point in prawns fed a diet containing 10% lipid. In addition, the mRNA expressions of hepatopancreatic diacylglycerol acyltransferase and acetyl-CoA carboxylase showed the highest values in prawns fed a 10% lipid diet. Conversely, there was a significant decrease in the mRNA expression of carnitine palmitoyltransferase-1a in the hepatopancreatic as dietary lipid levels increased. The highest mRNA expression of fatty acid-binding proteins was observed in prawns fed an 8% lipid diet. In conclusion, dietary lipid levels ranging from 8% to 11.79% are beneficial for ovarian maturation and health of M. rosenbergii broodstock.

A 30-day research was carried out to examine the impacts of dietary taurine (Tau) on ovaries maturation and physiological responses of Penaeus vannamei female brooders (29.4 ± 0.2 g). A basal diet (497 g kg⁻¹ protein and 140 g kg⁻¹ lipid) was administered with graded levels of Tau ranging from 0 (control) to 2, 4, 6, 8, and 10 g kg⁻¹. A total of 180 shrimp brooders were stocked into 18 250 L black circular polyethylene tanks. Female (n = 5) and male (n = 5) shrimps were stocked in each tank and supplied with seawater (35.2 ± 3.1 g L⁻¹ salinity, 28.9 ± 1.4°C) and the experimental feeds were offered to shrimp twice a day at 5% of their biomass. Supplementing diet with 4–8 g Tau kg⁻¹ reduced latency period after eye stalk ablation to spawning (5–6 days) that was associated with higher hepatopancreatic and gonadosomatic (except for 8 g Tau kg⁻¹ diet) indices (p<0.05). With 10 g Tau kg⁻¹ diet hepatopancreas glutathione peroxidase activity and total antioxidant capacity increased and catalase activity increased by 6 g Tau kg⁻¹ diet. Supplementing diet with Tau-enhanced bile-salt dependent lipase activity in the gut. Docosahexaenoic acid and Tau levels were elevated in the ovaries with the increment of dietary Tau level (p<0.05). Plasma total protein, calcium, cholesterol, and high-density lipoprotein increased with inclusion of 6–10 g Tau kg⁻¹ diet. The transcription levels of vitellogenin, insulin-like growth factor II, superoxide dismutase, prophenoloxidase, and lysozyme genes transcription levels were upregulated in the hepatopancreas of shrimp brooders fed 6–10 g Tau kg⁻¹ diet (p<0.05). It seems that Tau at 4–8 g kg⁻¹ diet by modulating lipid metabolism, antioxidant capacity, and immunocompetence can improve maturation and health status of P. vannamei brooders.

In this study, four groups of diet were prepared, with eel commercial diet without hydrolyzable tannin (HT) as the control group (H0), and the other three groups were fed with diet containing 0.05% (H1), 0.1% (H2), and 0.2% (H3) doses of HT to juvenile Mastacembelus armatus with an initial body weight of (0.40 ± 0.005) g. Juvenile fish in all groups were fed continuously for 60 days. Growth indices, hepatopancreatic antioxidant enzymes, biochemical indices (including total superoxide dismutase [T-SOD], catalase [CAT], malondialdehyde [MDA], total antioxidant capacity [T-AOC], alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [AKP], and triglyceride [TG]), the content of muscle amino acids and fatty acids, stomach and intestine enzyme activities (pepsin, amylase, lipase), and genes expressions were evaluated. The results showed that 0.1% HT significantly improved the growth performance, hepatopancreatic antioxidant capacity, as well as muscle quality and lipase activity of juvenile M. armatus. In summary, the optimal addition level of HT in the diet of juvenile M. armatus is 0.1%, which helps to improve aquaculture efficiency and improve the muscle quality of M. armatus. However, the long-term effects of feeding HT on M. armatus and its physiological reaction mechanism need to be further explored.

This study investigated the effect of dietary lipid levels on growth performance, lipid metabolism, antioxidant capacity, digestive enzyme activity, and metamorphosis rate of bullfrog (Aquarana catesbeianus) tadpoles. A total of six isonitrogenous diets were prepared, each containing 4.46% (L5), 6.95% (L7), 9.10% (L9), 10.90% (L11), 12.34% (L13), and 15.00% (L15) crude lipid content. The experimental diets were administered to triplicates of tadpoles (stage 25, 0.007 g) twice daily for 75 days with a daily feeding rate of 6.50% of their body weight. Weight gain (WG), specific growth rate (SGR), crude protein content of the whole body, apparent digestibility of dry matter and gross energy, intestinal lipase (LPS) capacity, lipoprotein lipase (LPL), and carnitine palmitoyltransferase-I (CPT-I) and contents of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in the liver, high-density lipoprotein cholesterol (HDL-C) content in the serum, and metamorphosis rate at stages 40 and 41 increased as the dietary lipid level increased from 4.46% to 12.34% and then decreased. As the dietary lipid level increased from 4.46% to 10.90%, the protein efficiency ratio (PER), protein deposition rate (PDR), lipid deposition rate (LDR), crude lipid content and gross energy of the whole body, apparent digestibility of the crude lipid, superoxide dismutase (SOD), catalase (CAT) activities in the liver, and the intestinal trypsin (TPS) activity all increased and then decreased. According to the second-order polynomial regression analysis of the WG and metamorphosis rate at stage 41 to the dietary lipid level, the ideal dietary lipid content for tadpoles was 11.08% and 10.72%, respectively. Overall, the appropriate dietary lipid level for bullfrog tadpoles was found to be 10.72%–11.08% of the diet.

Dietary docosahexaenoic acid (DHA) is crucial for the optimal (Opt) growth of bivalves, but the precise dietary DHA requirement remains undetermined in bivalves. Our study identifies the optimal dietary DHA requirement for razor clam Sinonovacula constricta and demonstrates its effects on fatty acid profiles and gene expression related to inflammation and detoxification. Microencapsulated feeds with different DHA levels (DHA1–6 groups: 1.68, 4.85, 9.49, 12.6, 15.59, and 16.95 mg g⁻¹ dry matter) were prepared using spray drying. Razor clams (initial wet weight: 3.8 ± 0.6 mg) were fed these microcapsules for a period of 20 days. The present study showed that the clams in the DHA1 group exhibited significantly lower weight and shell length gain rates compared to those in the DHA3, DHA4, DHA5, and DHA6 groups. Based on the shell length gain rate, the Opt dietary requirement of DHA for clam is approximately 6.42 mg g⁻¹ dry matter. The clams in the DHA2 group had significantly higher crude lipid content compared to those in the DHA1 and DHA6 groups, while the clams in the DHA1 group had the highest ash content, significantly higher than that in the DHA4 and DHA6 groups. The DHA levels in the clams increased with the increase in DHA content in the microcapsules, while the levels of total n-6 polyunsaturated fatty acids (PUFAs), linoleic acid (LA), and alpha-linolenic acid (ALA) decreased. The mRNA levels of cyclooxygenase-2 (cox2) and 5-lipoxygenase type 2 (5-lox-2) were higher in the DHA1 and DHA6 groups compared to other microcapsule groups. As dietary DHA levels increased, the mRNA levels of nuclear factor kappa B (nfκb) and nuclear factor erythroid 2-related factor 2 (nrf2) decreased. Additionally, the mRNA levels of glutamate-cysteine ligase catalytic subunit (gclc) and glutathione S-transferase (gst) were highest in the DHA1 group. This is the first study to determine the Opt DHA requirement for juvenile razor clams using microcapsules with different DHA levels, and this study further reveals that dietary DHA can help reduce inflammation and oxidative status in clams.

Manganese (Mn) is a nutritional element required for fish growth and physiology functions. In this study, we examined the effect of Mn on the intestinal digestive function, antioxidant response, and muscle quality in coho salmon (Oncorhynchus kisutch). Nine hundred salmons with initial weight approximately 0.35 g were fed with six isoproteic and isoenergetic diets formulated to contain 2.4, 8.5, 14.8, 19.8, 24.6, and 33.7 mg/kg Mn for 84 days. The result showed that the activity of trypsin and lipase was elevated, whereas α-amylase activity was not affected by various Mn diets in intestine. Dietary Mn elevated the activity of Mn-superoxide dismutase (Mn-SOD), total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX), and catalase (CAT), but had no influence on copper/zinc-superoxide dismutase (Cu/Zn-SOD) in intestine. Dietary Mn at 8.5, 14.8, 19.8, 24.6, and 33.7 mg/kg enhanced the gene expression level of protein kinase B (Akt) and mammalian target of rapamycin (mTOR). In addition, the accumulation of Mn in muscle was enhanced with increasing levels of dietary Mn. Dietary Mn elevated the content of sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca), but the content of iron (Fe) and Zn was decreased by dietary Mn in the salmon muscle. The content of fatty acids and amino acids was enhanced by various levels of dietary Mn in muscle. Moreover, a significant quadratic effect was observed on the texture of salmon muscle. The dietary Mn requirement was 16.9–25.7 mg/kg Mn to acquire the highest value of muscle texture using the quadratic regression model. The diets at 14.8 and 19.8 mg/kg Mn had a higher score of sensory evaluation for raw muscle. Our result showed that dietary Mn affected the intestinal digestion function and antioxidant response, which may further result in the change of muscle quality in coho salmon. The result will provide reference for detecting the effect of dietary micronutrients on the muscle quality of salmons.

One of the most farmed fishes is the African catfish, Clarias gariepinus. Its production has increased by 20% annually on average during the last 20 years, but the occurrence of fish diseases, especially bacterial such as Aeromonas hydrophila infections, is hindering its activities. Also, the incorporation of plant-derived substances in aquafeeds is limited since they frequently contain different antinutritional factors, like nonstarch polysaccharides (NSPs). However, supplementing fish diets with β-mannanase could increase growth, antioxidants, and immunity. Despite the advantage of β-mannanase, its effects on growth, digestive enzymes, antioxidants, and immunity in African catfish need to be elucidated. This study examined the effects of dietary β-mannanase on the growth performance, liver enzymes, antioxidant profiles, immunity, and protection of African catfish, C. gariepinus, against A. hydrophila infection. Five isonitrogenous diets were prepared to have 400 g/kg crude protein and supplemented with β-mannanase at 0, 1500, 3000, 4500, or 6000 thermostable endo, 1,4-β-mannanase units (TMUs)/kg diet and fed to 300 juveniles of the African catfish, C. gariepinus (mean weight 12.1 ± 0.1 g) for 12 weeks. Then, 10 fish from each tank received an intraperitoneal injection of 0.1 mL of A. hydrophila (5.0 × 10⁵ CFU/mL) and observed for 14 days. Results showed dietary β-mannanase levels considerably improved growth performance but did not affect fish survival. Also, amylase, protease, and lipase levels were significantly promoted in the fish fed with β-mannanase-fortified diets than the control group (p <0.05). Enhanced gut villi and intestinal absorption areas, haematlogical profiles, and liver enzymes but reduced gut viscosity were observed in fish-fed β-mannanase-fortified diets (p <0.05). In a dose-dependent order, including β-mannanase in the meals of African catfish raised the levels of glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione-S-transferase (GST), and glutamate cysteine ligase (GCL) activities and decreased the malondialdehyde (MDA) values in African catfish (p <0.05). Also, fish immunity was greatly (p <0.05) enhanced due to supplementation of the diet with β-mannanase. In addition, fish-fed diets comprising 6000 TMU β-mannanase/kg diet showed the lowest rates of fish mortality (7.5%) (p <0.05). Therefore, feeding African catfish, Clarias gariepinus, β-mannanase enhanced growth performance, increased activity of digestive enzymes, gut morphology, enhanced generation of short-chain fatty acids, digesta potential of hydrogen (pH), and improved antioxidant profiles and immunity at the optimum dose of 5800 TMU/kg diet. Additionally, β-mannanase protected African catfish against A. hydrophila infection.

The circular aquaculture model of largemouth bass pond engineering has the characteristics of high yield and efficiency, but it is prone to stress caused by flow velocity and density, which affects the yield of largemouth bass (Micropterus salmoides). γ-Aminobutyric acid (GABA) is believed to have the effect of improving growth and stress tolerance. We divided the largemouth bass into three groups: a control group, a flow rate and density combined stress group, and a combined stress feed supplemented with GABA (0.9%) group, and conducted a 60-day aquaculture experiment. The results showed that the final weight, weight gain rate (WGR), specific growth rate (SGR), and feed efficiency (FE) of largemouth bass significantly decreased in the combined stress group (P<0.05). The serum aspartate aminotransferase (AST), alanine transaminase (ALT) activity, and glucose (GLU), malondialdehyde (MDA) level of largemouth bass significantly higher than the control group, and the serum lysozyme (LZM) activity and total antioxidant capacity (T-AOC) were significantly lower than the control group (P<0.05). After adding GABA, the final weight, WGR, SGR, and FE decreased, and the serum GLU levels, AST, ALT activity, and MDA levels were downregulated, and the serum LZM activity and T-AOC of largemouth bass were upregulated. But most of the above are still at the level of the control group. Under combined stress, the messenger ribonucleic acid (mRNA) expression levels of growth hormone (GH), insulin-like growth factor-Ⅰ (IGF-I), B-cell lymphoma-2 (Blc2), nuclear transcription factor E2-related factor 2 (Nrf2), catalase (CAT), and superoxide dismutase (SOD) genes were significantly reduced (P<0.05), while the mRNA expression levels of heat stress protein 70 (HSP70), heat stress protein 90 (HSP90), nuclear factor kappa-B (NF-κB), interleukin-1β (IL-1β), Bax and keap1 genes were significantly increased (P<0.05). After the exogenous addition of GABA, all the above genes have a certain degree of callback, but GH, HSP70, HSP90, IL-1β, Bax, Nrf2, CAT, and SOD have not yet reached the level of the control group. These results indicate that adding GABA to feed can alleviate the adverse effects of combined stress of flow rate and density to a certain extent and provide insights for solving the problems in the circular aquaculture model of largemouth bass.

Long-term consumption of high-carbohydrate feed may adversely affect intestinal health of fish; however, the underlying roles remain ambiguous. This study examined the effects of varying carbohydrate levels on the intestinal flora of common carp and assessed how microbial metabolites influence intestinal health. Two hundred seventy common carps were chosen and distributed randomly into three groups that fed diets containing starch at levels of 15% (low-carbohydrate diet [LCD]), 28% (medium-carbohydrate diet [MCD]), and 45% (high-carbohydrate diet [HCD]) for 60 days. A significant increase in final body weight, weight gain rate, and specific growth rate within the MCD group, while feed conversion ratio exhibited a decrease in comparison to the other groups (p<0.05). Feeding with a HCD led to decreased activity of catalase and increased malondialdehyde content, which was consistent with reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) analysis results (p<0.05). Specifically, the RT-qPCR results revealed that HCD treatment significantly upregulated il1β, il6, and il8 transcript levels. Whereas, the il10 messenger RNA (mRNA) was markedly reduced in comparison to the LCD group. Furthermore, the HCD group exhibited an increased abundance of Proteobacteria, accompanied by a reduction in Fusobacteria abundance, and also revealed an upsurge in opportunistic pathogenic bacteria, such as Aeromonas and Shewanella. The correlation analysis demonstrated negative correlations of anti-inflammatory active substances such as fucoxanthin, (S)-reticuline, hecogenin, and uridine with Aeromonas, but positive correlations with Luteolibacter. In summary, dietary carbohydrates might mediate intestinal flora to regulate their metabolites and affect intestinal inflammatory response.

Porphyra polysaccharide (PPS), derived from marine red seaweeds of the Porphyra genus, has been reported to improve growth performance, lipid metabolism, and antioxidant capability in animals. The present study investigated the effects of PPS supplementation to a high-carbohydrate diet on growth performance, lipid metabolism, immunity, antioxidant capacity, intestinal morphology, and microbial composition in rabbitfish (Siganus canaliculatus). Rabbitfish were fed a basal starch diet (BSD, 15% starch) and high-starch diets (HSD, 25% starch) supplemented with varying levels of PPS (0%, 1.25%, 2.5%, and 5%) for 8 weeks. The results showed that HSD intake significantly decreased body weight and increased hepatosomatic index compared to rabbitfish fed BSD. But all dietary levels of PPS reversed these two indicators of fish fed HSD. In addition, the supplementation of 2.5% and 5% PPS significantly reduced the higher lipid contents in whole fish and abdominal muscle of fish fed HSD. Notably, 2.5% PPS reduced lipid droplets in the liver, possibly through the downregulation of genes associated with lipid synthesis and the upregulation of genes associated with lipid catabolism. Moreover, all levels of PPS supplementation decreased the higher serum alanine aminotransferase activity in fish fed HSD, indicating the alleviation of HSD-induced liver impairment. Additionally, PPS inclusion significantly increased the activity of serum lysozyme, superoxide dismutase, and catalase while decreasing serum malondialdehyde in fish fed HSD, suggesting improvements in immunity and antioxidant capacity. Furthermore, PPS inclusion mitigated damage to intestinal villi induced by HSD. Interestingly, 2.5% PPS increased the abundance of Bacteroidetes and Tenericutes while reducing the abundance of Proteobacteria and Spirochetes, indicating the reshaping of gut microbiota. In summary, dietary PPS alleviated the negative effects of HSD on growth performance, lipid metabolism, immunity, antioxidant capacity, and intestinal morphology and altered microbial composition in rabbitfish. This highlighted the beneficial effects of dietary PPS in fish and suggested it could contribute to the new strategies for treating metabolic syndrome and health impacts in aquatic animals.

In the past decade, insect meal has gained popularity in the animal feed industry, particularly in aquafeed, due to rising costs and decreased availability of fish meal (FM) and fish oil. Initially met with skepticism, insect meal is now seen as a promising ingredient because of its high nutrient profile. Research worldwide is exploring its potential as a FM replacement. Insects are abundant, nutritious, and environmentally friendly, as they can be reared on organic waste, minimizing the need for land, water, and energy. This research aims at obtaining a comprehensive and in-depth understanding of the current status and research trend patterns in this research field. To achieve this goal, this study conducts a mini systematic review and scientometric analysis of the global research published from 2013 to 2022 on the usage of insect meal in aquaculture. In the scientometric analysis, a total of 354 papers published by 1800 authors in 124 different journals from the Web of Science (WoS) core collection were analyzed, evaluating the number of publications, most relevant authors, organizations, top cited countries, most globally cited publications, and trending research themes in this field. The result showed that the University of Turin was the leading organization in insect meal research, whereas aquaculture was the leading journal, and author Laura Gasco was the prominent researcher in this field in the studied time frame (2013–2022). Italy was the leading country in Europe, while China dominated Asia in terms of the number of publications. The annual growth rate in insect meal research was found to be positive (23.11%), with 36.95 average citations per document. This study helps practitioners and scholars understand the current state of insect meal in aquaculture and identifies research requirements that can benefit both academia and industry.

Astaxanthin (Ax) determines the flesh redness of a salmonid fish which is the most desirable quality indicator by consumers. Fish cannot synthesize Ax de novo, therefore, the only way to increase flesh redness is to increase dietary input or improve the absorption and retention rate of dietary Ax. As a hydrophobic carotenoid, the absorption of Ax can be modulated by other lipid molecules in the diet. The present study explored the effect of three lipids, cholesterol (CH), phytosterol (PS), and docosahexaenoic acid (DHA) on Ax absorption, transport, and retention in rainbow trout. Dietary CH significantly improved Ax absorption by elevating plasma Ax levels (p<0.05); however, it had no effect on the whole body Ax or flesh color. Dietary PS appears to inhibit Ax absorption since fish had significantly (p<0.05) reduced whole body Ax. Dietary DHA appeared to have no effect on Ax absorption or retention. By comparing intestinal transcriptomes, a low density lipoprotein receptor (ldlr) gene was significantly downregulated in fish fed the CH diet as compared to the control diet. Since LDLR protein plays a major role in plasma lipoprotein turnover, we hypothesized that the inhibition of ldlr gene by high dietary CH resulted in higher retention of plasma Ax. The elevation of plasma Ax was not reflected in higher flesh coloration, which suggested other limiting factors governing Ax retention in the muscle. On the other hand, the transcriptomic and proteomic analyses found no changes of genes or proteins involved in Ax absorption, transport, or excretion in fish fed PS or DHA diets as compared to the control diet. In conclusion, this study has suggested that CH promotes Ax absorption by regulating lipoprotein retention and provide evidence for improving Ax absorption via dietary modulation.

Biofloc technology offers a viable choice for the rearing of fish seed by offering a safe and protected habitat for young fish. Nevertheless, it is crucial to establish a standardised stocking density and implement effective ameliorative steps in order to successfully utilise this technology. In this study, a 90-day investigation was conducted to assess the effect of stocking density and dietary vitamin C (Vit C) levels on the growth and immunity of Labeo gonius fry (1.03 ± 0.01 g) reared in a biofloc system. Three stocking density groups (5, 10 and 15 fish per 50 L) were established, and each experimental group was supplemented with three levels of Vit C (0, 500 and 1000 mg kg⁻¹). The highest survival rate was observed in the lowest density group (five fish per 50 L) fed with 1000 mg kg⁻¹ Vit C. A better feed conversion ratio and significantly higher protein efficiency ratio were found in the moderate stocking density group (10 fish per 50 L) fed with 500 mg kg⁻¹ Vit C. Total leukocyte count (TLC), haemoglobin, and packed cell volume improved in Vit C-fed groups. The total erythrocyte count (TEC) increased in groups fed Vit C and stocked at lower densities (5 and 10 fish per 50 L). Total serum protein (TPP) content increased when Vit C was added at a rate of 500 mg kg⁻¹. Serum glucose and cortisol levels were significantly reduced in Vit C-supplemented groups. Supplementation of Vit C at 500 mg kg⁻¹ resulted in a significantly lower value of malondialdehyde (MDA). Thus, the findings confirm that the incorporation of Vit C in the basal diet promotes the growth and health status of L. gonius fry reared in the biofloc system at high-density rearing.

A 10-week feeding trial was conducted to investigate the dietary pyridoxine requirements of coho salmon (Oncorhynchus kisutch) post-smolts with an initial mean body weight of 180.22 ± 0.41 g. Seven diets were prepared with gradient pyridoxine levels of 0.32, 1.25, 2.56, 4.08, 8.24, 16.02, and 32.32 mg/kg, respectively, and each diet was assigned to three replication groups of 10 fish. The results revealed that coho salmon fed the diet with pyridoxine supplementation gained more final body weight (FBW), specific growth rate (SGR), and better feed conversion ratio (FCR). FBW and SGR of the fish fed the diet with 8.24 mg/kg pyridoxine were significantly higher than those of the other groups (P<0.05). An inverse trend was observed for FCR, which was the lowest in fish fed the diet with 8.24 mg/kg pyridoxine. The gradient pyridoxine levels did not yield any statistically (P>0.05) significant impact on the whole-body composition including moisture, ash, crude lipid, and crude protein. The hepatic pyridoxine concentration, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities increased significantly with dietary pyridoxine levels increasing from 0.32 to 4.08 mg/kg (P<0.05) and plateaued after that (P>0.05). The coho salmon fed the diet with 8.24 mg/kg pyridoxine achieved the maximum superoxide dismutase and catalase, as well as the minimum total cholesterol, triglyceride, and malondialdehyde. Broken line analysis of SGR, FCR, AST, and ALT activities reflected the optimal dietary pyridoxine requirements for coho salmon post-smolts from 3.92 to 7.08 mg/kg diet.