Protein-sparing effect of dietary lipid: Changes in growth, nutrient utilization, digestion and IGF-I and IGFBP-I expression of Genetically Improved Farmed Tilapia (GIFT), reared in Inland Ground Saline Water

From feed formulation to frozen flesh: Hydrolysable tannin mitigates high-fat diet-induced quality deterioration in flesh of largemouth bass (Micropterus salmoides) through enhancing antioxidant capacity, optimizing nutrient composition, and textural characteristics

This study aimed to systematically evaluate the impact of adding hydrolysable tannin (HT, 1.25 g/kg) to a high-fat diet on the flesh quality of fish (Micropterus salmoides) after 12 weeks rearing. Results showed that high-fat diet supplemented with HT increased the content of crude protein and n-3 polyunsaturated fatty acids and optimized the amino acid composition of flesh. Meanwhile, the high-fat diet reduced the antioxidant capacity, muscle fiber density, and collagen content of flesh, but HT supplementation counteracted these negative effects. According to metabolomics analysis, dietary HT reduced the abundance of hypoxanthine and inosine, suggesting that HT might potentially mitigate the deterioration of flesh by delaying the degradation of adenosine triphosphate. Short-term frozen storage analysis indicated that dietary HT contributed to maintain flesh color, texture, and pH, and reduce total volatile base nitrogen‌. This study provides insights for enhancing the nutritional value and flesh quality of fish fed high-fat diets.

Transcriptomic analysis reveals sexual dimorphism in lipid metabolism within largemouth bass (Micropterus salmoides) fed the high-fat diet

The study presented the differential responses of male and female largemouth bass fed a high-fat diet, focusing on growth performance, hepatic transcriptomics, and lipid metabolism. The high-fat diet, 50.23 % crude protein and 19.46 % crude fat, was formulated and fed to female and male largemouth bass for 73 days separately. Growth parameters, such as final weight, weight gain (WG) and specific growth rate (SGR), demonstrated superior performance in males compared to females fed the high-fat diet. Hepatic transcriptomic analysis between the sexes under high-fat diet revealed totally 267 differentially expressed genes (DEGs), of which 132 were up-regulated and 135 down-regulated. Notably, genes implicated in lipid biosynthesis, such as elovl5, pap, aacs, hmgcra, fdft1, ebp, and dhcr24, were found to be down-regulated in males and are enriched in metabolic pathways. This suggests a sex-dependent modulation of lipid metabolism. Furthermore, the study revealed a stark contrast in hepatic mRNA expression levels of genes pivotal for lipid anabolism, with acc1, pparγ, srebf1, fasn, and scd being more highly expressed in females compared to males. Conversely, genes associated with lipid catabolism, including cpt1 and hsl, showed elevated expression in males. These findings underscore the interplay between sex, diet, and metabolic regulation in largemouth bass. The study's contributions to our understanding of physiological variances between male and female largemouth bass under high-fat diet are significant, offering valuable insights for the nutritional strategies to accommodate the metabolic needs of both sexes.

Effects of Diets With Different Carbohydrate to Lipid Ratios on the Growth Performance, Ion Transport, and Carbohydrate, Lipid and Ammonia Metabolism of Nile Tilapia (Oreochromis niloticus) Under Long-Term Saline-Alkali Stress

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.

Do lipases and amylases of an endangered Indian carp Hypselobarbus pulchellus play a role in visceral fat dynamics; evidence of in vitro macromolecular interactions

Fat depots or triglycerides are hydrolysed by the action of lipases in fish to be used for energy and/or for growth and reproduction. In herbivores fishes, de novo synthesis of lipids from non- lipid substrates (glucose) leads to fat deposits and/or fatty infiltration in organs especially on ovaries limiting its normal functions. This study was aimed to understand lipases from the digestive tract (DT) of adult Hypselobarbus pulchellus of different sizes, their partial purification, characterisation and their isozymes. In-vitro hydrolysis study on interaction of carbohydrate with proteins was evaluated to establish specific protein selection that combat undue glucose release. Results of the study identified four lipase isoenzymes of ~ mol. wt 19.88, 24.29, 32.86, 54.56 kDa with optimal pH of 3.5 and 8, pH stability between pH 5.5-10; optimal temperature at 35 °C and heat stability between 35 and 45 °C. Characterisation studies indicated presence of thiol group in their active site and Ca, Na and Zn ions activated lipase activity. Rice bran as carbohydrate source when used along with azolla (plant protein) and fish meal (animal protein) may combat undue release of excess glucose that leads to visceral fat formation in H. pulchellus as assessed from in vitro studies.

Hoven's carp Leptobarbus hoevenii strategized metabolism needs to cope with changing environment

Current water warming and freshwater acidification undoubtedly affect the life of aquatic animals especially ammonotelic teleost by altering their physiological responses. The effect of temperature (28 °C vs 32 °C) and pH (7 vs. 5) on the metabolic compromising strategies of Hoven's carp (Leptobarbus hoevenii) was investigated in this study. Fishes were conditioned to (i) 28 °C + pH 7 (N28°C); (ii) 32 °C + pH 7 (N32°C); (iii) 28 °C + pH 5 (L28°C) and (iv) 32 °C + pH 5 (L32°C) for 20 days followed by osmorespiration assay. Results showed that feeding performance of Hoven's carp was significantly depressed when exposed to low pH conditions (L28°C and L32°C). However, by exposed Hoven's carp to L32°C induced high metabolic oxygen intake and ammonia excretion to about 2x-folds higher compared to the control group. As for energy mobilization, Hoven's carp mobilized liver and muscle protein under L28°C condition. Whereas under high temperature in both pH, Hoven's carp had the tendency to reserve energy in both of liver and muscle. The findings of this study revealed that Hoven's carp is sensitive to lower water pH and high temperature, thereby they remodeled their physiological needs to cope with the environmental changes condition.

Integrated alternative approaches to select feed-efficient rainbow trout families to enhance the plant protein utilization

Improving feed utilization efficiency is a challenge in aquaculture. Therefore, we developed an indirect benchmark to use in selecting trout for improved efficiency of feed utilization on plant protein (soy)-based diets, with the long-term goal of reducing the cost of commercial trout production. We used a four-part integrative approach to identify feed efficient individuals among 1595 fish coming from 12 genetically selected families by establishing the phenotypic relationship between feed conversion ratio (FCR) and body weight variations using compensatory feeding regimes. Additionally, we examined the nutritional composition of fish filet for each efficiency phenotype during the compensatory regimen. Our findings showed that the fish with the lowest weight loss during a feed deprivation period and the highest weight gain during the refeeding period (FD-/RF +) demonstrated the lowest FCR (FCR = 0.99) and consisted of individuals from several lines. This finding confirms the possibility of improving feed efficiency in mixed lines. Although feeding period has an effect on nutritional composition of fillet, such selection criteria did not show an effect on groups. Overall, successful selection for the improvement of feed efficiency will have a broad application to commercial fish selective breeding programs, leading to increased aquaculture sustainability in the long run.

Effects of Dietary Protein and Lipid Levels on Growth, Metabolism, Antioxidative Capacity, and Fillet Quality of Adult Triploid Rainbow Trout Farmed in Net Cage

The research is aimed at investigating the effects of dietary protein and lipid levels on adult triploid rainbow trout growth performance, feed utilization, digestive and metabolic enzyme activities, antioxidative capacity, and fillet quality. Nine diets containing three dietary protein levels (DP) (300, 350, and 400 g kg^-1) and three dietary lipid levels (DL) (200, 250, and 300 g kg^-1) were prepared using a 3 × 3 factorial design. In freshwater cages, 13,500 adult female triploid rainbow trout (3.2 ± 0.1 kg) were cultured for 77 days. Triplicate cages (500 fish per cage) were used as repetitions of each experimental diet. The findings revealed that as DP increased to 400 g kg^-1 and DL raised to 300 g kg^-1, the weight gain ratio (WGR) elevated significantly (P < 0.05). However, when DP ≥ 350 g kg^-1, WGR was similar in the DL250 and DL300 groups. As DP raised to 350 g kg^-1, the feed conversion ratio (FCR) notably decreased (P < 0.05). In the DP350DL300 group, lipids had a protein-sparing impact. High DP diet (400 g kg^-1) generally improved fish health status by increasing antioxidant capacity in the liver and intestine. A high DL diet (300 g kg^-1) showed no harmful effect on hepatic health based on plasma levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and antioxidant capacity in the liver. For fillet quality, a high DP diet could increase fillet yield, improve fillet hardness, springiness, and water-holding capacity values, and inhibit the production of off-flavors caused by n-6 fatty acids. A high DL diet could increase odor intensity, and EPA, DHA, and n-3 fatty acid concentrations decrease the thrombogenicity index value. The maximum fillet redness value was discovered in the DP400DL300 group. Overall, for adult triploid rainbow trout (≥3 kg), the minimum recommended DP and DL according to growth performance were 400 and 250 g kg^-1, respectively; DP and DL based on feed utilization were 350 and 200 g kg^-1, respectively; DP and DL based on fillet quality were 400 and 300 g kg^-1, respectively.

Attenuated glucose uptake promotes catabolic metabolism through activated AMPK signaling and impaired insulin signaling in zebrafish

Glucose metabolism in fish remains a controversial area of research as many fish species are traditionally considered glucose-intolerant. Although energy homeostasis remodeling has been observed in fish with inhibited fatty acid β-oxidation (FAO), the effects and mechanism of the remodeling caused by blocked glucose uptake remain poorly understood. In this study, we blocked glucose uptake by knocking out glut2 in zebrafish. Intriguingly, the complete lethality, found in Glut2-null mice, was not observed in glut2^-/- zebrafish. Approxiamately 30% of glut2^-/- fish survived to adulthood and could reproduce. The maternal zygotic mutant glut2 (MZglut2) fish exhibited growth retardation, decreased blood and tissue glucose levels, and low locomotion activity. The decreased pancreatic β-cell numbers and insulin expression, as well as liver insulin receptor a (insra), fatty acid synthesis (chrebp, srebf1, fasn, fads2, and scd), triglyceride synthesis (dgat1a), and muscle mechanistic target of rapamycin kinase (mtor) of MZglut2 zebrafish, suggest impaired insulin-dependent anabolic metabolism. Upregulated expression of lipolysis (atgl and lpl) and FAO genes (cpt1aa and cpt1ab) in the liver and proteolysis genes (bckdk, glud1b, and murf1a) in muscle were observed in the MZglut2 zebrafish, as well as elevated levels of P-AMPK proteins in both the liver and muscle, indicating enhanced catabolic metabolism associated with AMPK signaling. In addition, decreased amino acids and elevated carnitines of the MZglut2 zebrafish supported the decreased protein and lipid content of the whole fish. In summary, we found that blocked glucose uptake impaired insulin signaling-mediated anabolism via β-cell loss, while AMPK signaling-mediated catabolism was enhanced. These findings reveal the mechanism of energy homeostasis remodeling caused by blocked glucose uptake, which may be a potential strategy for adapting to low glucose levels.

The influence of napier grass biomass mixed feed on the biorefinery indicator for Nile tilapia production

Aquaculture is vital for feeding a growing population as aquatic creatures require more protein. Utilizing protein-rich biomass for feeding animals is a possible solution. Biorefinery technology can extract protein and non-protein components from biomass, creating an economically feasible value chain. This study replaced fish feed with napier grass and used a compensatory response to reduce the cost of feeding Nile tilapia. The trial involved dividing mono-sex male Nile tilapia, initially weighing between 11.10 and 13.60 g/f, into four groups with three replications based on their feeding regime. Therefore, in the study, four groups of Nile tilapia were fed different diets for 90 days. The control group (T1) received a commercial floating pellet diet throughout the trial. Group T2 and T3 received a mix of commercial floating pellet diet and napier grass in varying proportions, and group T4 was fed with only napier grass throughout the trial. The study found that groups T2 and T3 had remarkable fish growth performance, high digestibility of napier grass, and lower feed prices with the highest benefit-cost ratios. The percentage of edible flesh and Hepatosomatic Index (PT2) were higher in group T2 than T3. Cellulase activity decreased with the frequency of napier grass intake, and the amylase activity was higher in T2 than T3, which also had the highest growth performance and feed utilization. Therefore, the study suggests that the optimal feeding regimen for Nile tilapia is T2 or T3, which promotes growth and is cost-effective.

Guar gum improves growth performance, intestinal microbiota homeostasis, and hepatic lipid metabolism in juvenile largemouth bass (Micropterus salmoides) fed high-fat diets

The study aimed to investigate the effects of guar gum on the growth performance, gut microbiota composition, and hepatic lipid metabolism of largemouth bass (Micropterus salmoides) fed high-fat diets. Experimental fish were fed a normal-fat diet (Control), high-fat diet (HF), or HF diets supplemented with 0.3 %, 1 %, and 3 % guar gum (GG0.3, GG1, and GG3, respectively) for eight weeks. The results showed that HF significantly decreased fish growth performance, increased hepatic lipid accumulation, upregulated the expression of sterol regulatory element binding proteins 1 (SREBP1), and downregulated the expression of liver X receptor alpha (LXRα), cytochrome P450 7A1 (CYP7A1), and CYP8B1, compared to Control. However, these problems of high-fat diets were significantly alleviated by GG 0.3. The intestinal microbial communities of the GG0.3 and Control were similar but distinctly different from that of the HF group. Compared to HF, GG0.3 significantly increased the relative abundances of Firmicutes and Lactococcus and decreased the relative abundance of Tenericutes, Mesomycoplasma, and Phenylobacterium. In addition, the GG0.3 and GG1 treatments significantly enhanced the bile salt hydrolase (BSH) activity in the digesta compared to HF. In conclusion, 0.3 % guar gum supplementation can improve growth performance, intestinal health, and hepatic lipid metabolism in fish fed high-fat diets.

Effect of Dietary Lipid Level on Growth Performance, Body Composition, and Physiometabolic Responses of Genetically Improved Farmed Tilapia (GIFT) Juveniles Reared in Inland Ground Saline Water

A 60-day feeding trial was carried out to determine the effect of dietary lipid levels on growth and physiometabolic responses to optimize the dietary lipid requirement for maximizing the growth of Genetically Improved FarmedTilapia (GIFT) juveniles reared in inland ground saline water (IGSW) of medium salinity (15 ppt). Formulation and preparation of seven heterocaloric (389.56-449.02 Kcal digestible energy/100 g), heterolipidic (40-160 g/kg), and isonitrogenous (410 g/kg crude protein) purified diets were done for conducting the feeding trial. Random distribution of 315 acclimatized fish (mean weight 1.90 ± 0.01 g) was made in seven experimental groups such as CL4 (40 g/kg lipid), CL6 (60 g/kg lipid), CL8 (80 g/kg lipid), CL10 (100 g/kg lipid), CL12 (120 g/kg lipid), CP14 (140 g/kg lipid), and CL16 (160 g/kg lipid) with 15 fish per triplicate tank (fish density, 0.21 kg/m3). Respective diets were used for feeding the fish at satiation level three times daily. Results indicated that weight gain percentage (WG%), specific growth rate (SGR), protein efficiency ratio, and protease activity significantly increased up to 100 g lipid/kg fed group, and then the values significantly decreased. Muscle ribonucleic acid (RNA) content and lipase activity were highest in 120 g/kg lipid-fed group. RNA/DNA (deoxyribonucleic acid) and serum high-density lipoproteins levels of 100 g/kg lipid-fed group were significantly higher than 140, and 160 g/kg lipid-fed groups. The lowest feed conversion ratio was found in the 100 g/kg lipid-fed group. The amylase activity was significantly higher in 40 and 60 g lipid/kg fed groups. The whole-body lipid level was increased with increasing the dietary lipid levels, whereas, there was no significant difference in whole-body moisture, crude protein, and crude ash contents of all groups. Highest serum glucose, total protein and albumin, and albumin to globulin ratio and lowest low-density lipoproteins level were found in 140 and 160 g/kg lipid-fed groups. Serum osmolality and osmoregulatory capacity did not vary significantly, whereas carnitine palmitoyltransferase-I and glucose-6-phosphate dehydrogenase showed an increased and decreased trend, respectively, with the increasing dietary lipid levels. According to second-order polynomial regression analysis based on WG% and SGR, the optimum dietary lipid for GIFT juveniles in IGSW of 15 ppt salinity was found to be 99.1 and 100.1 g/kg, respectively.

Synbiotic Lactic Dry® enhanced the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater

Nile tilapia is recognized as a suitable candidate for intensive farming and sustainability of the aquaculture industry. However, one issue limiting Nile tilapia expansion in arid and semi-arid areas is the scarcity of freshwater resources. In this study, the supplementation of synbiotics was investigated to enhance the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater. Four diets were prepared where the basal diets were mixed with the dietary mixture of probiotics and prebiotics (Synbiotic Lactic Dry®, a blend of Saccharomyces cerevisiae, Lactobacillus acidophilus, Streptococcus faecium, and Bacillus subtilis, mannan oligosaccharides and β-1.3/1.6-D-glucan) at 0, 0.5, 1, and 2 g/kg. After eight weeks, the final weight and weight gain are linearly increasing with increasing the supplementation level of synbiotic. Markedly fish fed 0.5, 1, and 2 g/kg of synbiotic had higher final weight, weight gain, and feed intake and lower feed conversion ratio (FCR) than fish fed synbiotic free diet. The specific growth rate (SGR) was significantly higher in fish fed 1 and 2 g/kg than in fish fed 0 and 0.5 g/kg. The intestine of fish fed on synbiotic shows an increase in intestinal villi density. Further, the intestine of fish fed on synbiotic showed an increase in the length and branching intestinal villi (anterior, middle, and posterior) in a dose-dependent manner. The lysozyme and phagocytic activities were significantly different from the control, while synbiotic supplementation did not affect the phagocytic index. Interestingly, the results showed marked upregulation of ghrelin, IGF-1, and GH genes in fish fed synbiotics at 0.5, 1, and 2 g/kg. In addition, fish fed 2 g/kg had the highest expression of ghrelin, IGF-1, and GH genes. In conclusion, growing Nile tilapia in inland brackish groundwater can be achieved without negative impacts on the growth performance and health status. Supplementing synbiotics (1-2 g/kg) in Nile tilapia feeds enhanced the growth and feed performances, intestinal histomorphological features, growth-related genes, and immune response.