Diet-fed Fish Research Articles

Dietary chitosan positively influences the immunity and reproductive performances of mature silver barb (Barbonymus gonionotus)

This research was carried out to assess the effects of dietary chitosan on the immunity and reproductive performance of adult Barbonymus gonionotus. The fish (average weight 66.7 ± 0. 86 g) were randomly divided into four treatments: control (0.00 g/kg), CHT-1 (1.00 g/kg), CHT-2 (2.00 g/kg) and CHT-3 (3.00 g/kg) and were fed the appropriately formulated diets for 60 days. The results showed significant differences in the immunological parameters such as lymphocytes, neutrophils, monocytes, immunoglobulin (IgM), and lysozyme activity in the chitosan-fed fish compared to those in the control diet-fed fish. The reproductive hormones such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were significantly enhanced in chitosan fed fish compared to the control. Furthermore, the chitosan-treated diet significantly improved the reproductive performance of adult B. gonionotus compared to control fish. Qualitative histological studies showed that chitosan significantly improved egg morphology and showed mature and uniformly sized eggs compared to the control fish. Similarly, a quantitative histological investigation revealed that chitosan significantly increased oocyte area (µm2) and number of oocyte-3 compared to the control. In conclusion, our study found that dietary chitosan at optimal dose of 1.00 g chitosan/kg feed enhanced immunity, regulated reproductive hormone levels, and promoted reproductive performance and ovarian development in B. gonionotus.

Effects of dietary supplementation of natural Spirulina on growth performance, hemato-biochemical indices, gut health, and disease resistance to Aeromonas hydrophila of Stinging catfish (Heteropneustes fossilis) fingerling

Spirulina is a popular edible blue-green alga that has piqued the interest of aqua-feed formulations due to its high concentration of micronutrients, macronutrients, and antioxidants. To investigate the impacts of natural Spirulina as a feed additive on Stinging catfish (Heteropneustes fossilis) growth, feed utilization, hematology and serum biochemistry, gut morphology, as well as disease resistance to Aeromonas hydrophila, a 60-day feeding experiment was performed. The fish (N = 240), with an initial weight of 4.23 ± 0.50 g, were placed in 12 aquaria tanks (100 L/ tank) and fed twice daily until they were satisfied. Four different experimental diets: 0% (D0, control diet), 1% (D1), 3% (D2), and 5% (D3) natural Spirulina meal were used to feed the fish. This study found that Stinging catfish fed with a 5% Spirulina diet obtained notably higher (p < 0.05) specific growth rate, final weight, weight gain, and average daily weight gain than other supplemented regimens. Furthermore, as Spirulina inclusion in diets increased, feed utilization parameters such as feed conversion ratio and protein efficiency ratio improved remarkably (p < 0.05). Red blood cell, white blood cell, lymphocytes, neutrophil, monocytes, basophil, hemoglobin, red cell distribution width-standard deviation, and mean corpuscular hemoglobin were all substantially (p < 0.05) greater in 5% Spirulina diet-fed fish. The basal diet-fed fish had lower (p < 0.05) total protein, globulin, and albumin levels and higher glucose, cholesterol, and triglyceride levels than those fed with other test diets. Compared to other fish groups, light microscopic examination of intestinal tissues revealed that fish fed 3% and 5% Spirulina had well-organized enterocytes, intact epithelial barrier, abundant goblet cells, and lacking luminal cell debris, as well as exhibited no signs of inflammation (edema). Spirulina diets significantly (p < 0.05) affected intestinal villi height and width, mucosa width, crypt depth, villi, and lumen area. Furthermore, a 5% Spirulina diet-fed fish demonstrated remarkably (p < 0.05) greater resistance (68.57%) to A. hydrophila during the bacterial challenge trial. Based on the findings, applying natural Spirulina powder at 5% in diets as a feed supplement could benefit H. fossilis nutrient utilization, growth performance, health status, as well as disease resistance.

Replacement of fishmeal by house cricket (Acheta domesticus) and field cricket (Gryllus bimaculatus) meals: Effect for growth, pigmentation, and breeding performances of guppy (Poecilia reticulata)

Insect meal is a promising alternative to unsustainable fishmeal. However, limited studies have been focused on identifying the fishmeal replacement potential related to ornamental fish compared with food fish. Therefore, an experiment was conducted using house cricket (Acheta domesticus) and field cricket (Gryllus bimaculatus) meals to test the growth and pigmentation performances of Guppy (Poecilia reticulata). The protein content of the fish meal in the control diet was replaced by 50%, 75%, and 100% by both cricket meals. One-day-old fry of all the treatments were initially fed by Artemia nauplii for five days; then, the research diets were fed from day six to day thirty thrice a day ad libitum by the respective research diets. The growth performance of all the treatments was significantly similar (p > 0.05) to each other and the control. Therefore, the results confirmed that both insect meals could replace fishmeal by 100% without any adverse effects on the growth of the nursery phase of P. reticulata. Furthermore, sorted and further reared fry were tested for breeding performance, and the results showed that both insect meals did not affect negatively (P > 0.05) the delivered fry number and its weight and length. The total carotenoid concentration and MATLAB analysis of the photographed caudal fins of A. domesticus meal-fed fish showed that all the inclusion levels of the insect meal did not affect (P > 0.05) pigmentation with the control. However, the diet that the field cricket meal included diet-fed fish replaced 100% fishmeal showed statistically higher (P < 0.05) color intensity than the control. Pigmentation is a crucial factor for ornamental fish in marketing. Therefore, the field cricket meal is more suitable than house cricket for P. reticulata feed.

Trehalose alleviated hepatic cholesterol accumulation via inhibiting transformation from glucose-derived acyl-CoA to cholesterol synthesis in Nile tilapia

Trehalose has been identified as an autophagy enhancer with atheroprotective properties in mammals that reduces cholesterol accumulation in the body. However, such effects have been rarely explored in aquatic animals. This study examined the effects of trehalose supplementation in a high-cholesterol diet on liver cholesterol accumulation and the related mechanisms in Nile tilapia (Oreochromis niloticus). The fish were fed high cholesterol (1.6%) diets supplemented with different levels (0, 1.5, 3 and 4.5%) of trehalose for eight weeks. The results showed that inclusion of 3% trehalose in high-cholesterol diet led to the significant reduction of viscerosomatic index (VSI), hepatosomatic index (HSI) and total and free cholesterol (TC and FC) accumulation in the serum and liver of fish. Moreover, 3% trehalose supplementation decreased serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, indicating the alleviation of high-cholesterol diet-induced liver impairment. Surprisingly, such beneficial effects did not correlate with autophagy activity since dietary inclusion of 3% trehalose inhibited the expression of autophagy-related genes and proteins (atg5/12, autophagy related gene 5/12; Lc3, microtubule-associated protein 1 light chain 3 and Beclin protein). Also, the same group inhibited the expression of genes related to hepatic cholesterol synthesis, glycogen metabolism, glycolysis, and glucose oxidative phosphorylation. These results indicated that trehalose treatment reduced the capability of glucose catabolism in the liver of high-cholesterol diet-fed fish. In the primary hepatocytes of Nile tilapia, which were cultured in a medium containing high cholesterol concentration, the [1-14C]-glucose tracking test showed that trehalose treatment resulted in decreased cellular retention of 14C-glucose and unaltered release of 14CO2. Likewise, the trehalose treatment inhibited the expression of genes associated with glucose uptake and catabolism, cholesterol synthesis. Also, the inhibited autophagy activities were found in the primary hepatocytes treated with trehalose. Overall, trehalose treatment alleviated high-cholesterol diet-induced hepatic and serum cholesterol accumulation in Nile tilapia, but such effect was not associated with the autophagy activities. Alternatively, our results suggested that trehalose exerted a cholesterol-lowering effect via inhibiting the transformation from glucose-mediated acyl-CoA to cholesterol synthesis in the liver of fish. This is the first study revealing the cholesterol-lowering function of trehalose in fish and could contribute to developing new strategies for maintaining liver health in fish.

Mitigating Aeromonas hydrophila infection in Nile tilapia through dietary Basella alba and Withania somnifera supplementation: A bioassay‐guided fractionation approach

The present study aimed to identify the antibacterial bioactive compounds in Withania roots and Basella leaves against Aeromonas infection in Nile tilapia. Withania ethanol extract (EW, ZoI 10.72 ± 1.028 mm) and Basella methanol extract (MB, ZoI 10.83 ± 1.058 mm) showed the highest antibacterial activity in disc diffusion assay. In in vivo experiment, Nile tilapia (25.61 ± 0.31 g) were fed basal, EW and MB (both at 0.7 g/kg feed) diets for 15 days either before being intraperitoneally injected with Aeromonas and basal diet feeding for 7 days (prophylactic) or after bacterial injection and basal diet feeding for 7 days (therapeutic). Fish fed EW and MB fortified diets showed significantly (p < 0.05) lower mortality, alkaline phosphatase, glutamic oxaloacetic transaminase, glutamic pyruvate transaminase activities, HSP70, Caspase3, IFN-ɣ, IL-1 β, TNF-α level, while significantly (p < 0.05) higher weight gain, protein efficiency ratio, respiratory burst, lysozyme, phagocytotic activity, plasma total protein, total immunoglobulin content, RBC, WBC count, haemoglobin, haematocrit, mean corpuscular haemoglobin concentration, mean corpuscular volume, lymphocytes, neutrophils, monocytes percentages and superoxide dismutase, catalase, glutathione peroxidase activities compared to basal diet-fed fish. EW showed significantly (p < 0.05) better antibacterial efficacy compared to MB. Prophylactic treatment showed better results compared to therapeutic treatment. Bioassay-guided chromatography and GC–MS analysis revealed the presence of hexadecanoic acid, phytol, cis, cis, cis-7,10,13-hexadecatrienal in EW and α-tocopherol, 1-(+)-ascorbic acid 2,6-dihexadecanoate, 1-heptatriacotanol in MB, which was reported to have antibacterial, antioxidative and immunostimulatory potential. Present results indicate prospective use of EW as a prophylactic immunostimulant and effective therapeutic remedy against Aeromonas in Nile tilapia.

Evaluation of UV-B Ameliorating Properties of Indigenous Plants Ashwagandha Withania somnifera (Dunal), Amla Emblica officinalis (Gaertn), and Prickly Chaff Flower Achyranthes aspera (L.) Supplemented Diets in Prior UV-B Exposed Catla catla

Ultraviolet B (UV-B) radiation is a potent environmental stressor and it severely affects the survival, growth, and physiology of aquatic organisms. The UV-B protective properties of three herbal ingredients enriched diets were evaluated in pre-exposedCatla catla. Fish (70.38 ± 1.18 g) were divided into five sets with three replicates each. Four sets were exposed to UV-B (80 µW/cm2) for an initial 10 days (20 min/day), and the fifth one remained unexposed (control). On day 11, feeding with enriched diets started. These diets were: diet 1 (D1) containingWithania somnifera(0.5%) root powder, diet 2 (D2) containingEmblica officinalis(1.25%) fruit powder, diet 3 (D3) containing seeds ofAchyranthes aspera(0.5%), and diet 4 (D4) control. There were two batches of D4 diet-fed fish, D4a, UV-B exposed, and D4b unexposed. Blood and tissue samples were collected on days 0, 7, 14, and 21 of feeding. The average weight reduced 26.32% in UV-B exposed catla compared to the unexposed one on day 0. Among the exposed fish, average weight was significantly higher in D3 compared to others throughout the study period. Significantly lower nitric oxide synthase (NOS) and higher thiobarbituric acid reactive substances (TBARS), carbonyl protein, superoxide dismutase (SOD), and heat shock proteins (Hsp) 70 and 90 were observed in D4a compared to the enriched diet fed catla. The NOS level was significantly higher in D3 on day 21. The TBARS level was significantly lower in D3 on days 7 and 14 and in D2 and D3 on day 21. The carbonyl protein, SOD, and Hsp70 levels were always significantly lower in D3 compared to others, and D2 followed D3 treatment. Hsp 90 was significantly lower in D2 compared to others on day 7 and in D3 on days 14 and 21. All three enriched diets helped the fish overcome the harmful effect of UV-B radiation, and the D3 diet-fed fish showed the best performance.

Bioconversion of chitin waste through Stenotrophomonas maltophilia for production of chitin derivatives as a Seabass enrichment diet

Marine wastes pose a great threat to the ecosystem leading to severe environmental hazards and health issues particularly the shellfish wastes. The shellfish waste which contains half of the amount of chitin can be efficiently transformed into useful products. Various approaches for the hydrolysis of chitin like physical, chemical, and enzymatic processes are there. Still, the use of enzyme chitinase is well documented as an effective and eco-friendly method. The present study summarizes the isolation of chitinase enzyme producing bacteria from different shrimp waste disposal sites in Parangipettai (India), and the possible use of an enzyme hydrolyzate as an immunostimulant to Asian Seabass (Lates calcarifer). The potential chitinase-producing bacteria were identified by 16S rRNA gene sequencing as Stenotrophomonas maltophilia. After purification, the chitinase specific activity was 5.01 (U/ml) and the protein content was 72 mg and the recovery rate was 48.06%. The optimum pH and temperature for the chitinolytic activity were 6.5 and at 35–50 °C, respectively. The animal experiment trial was done with our feed supplements which included 0.0 (control), 0.5%, 1% and 2% of chitin degraded product. All the supplementary feed had an optimal 42% (w/w) of crude protein. The feed protein level was 41–43% on average and gross energy was 13–17 kcal/g and the feed was observed to exhibit a significantly higher (p < 0.05) survival rate, condition factor, specific growth rates, and body weight gain was also found to be promising compared to other fishes fed with control diet only. The red blood cells (RBC) and white blood cell (WBC) counts were found to increase significantly after being challenged with infection in animals fed with chitin derivatives from 1st week to 3rd week when compared to the control. The hematocrit (Hct) values were low on the 2nd and 3rd week in infected fish fed with chitin derivatives. This low level was due to infection lyses of the red blood cells and increased nitro blue tetrazolium reduction. The control diet-fed fish showed 70% mortality but the chitin derivative supplemented fishes showed only 20% mortality post-infection. The results of the study encompass that the use of chitin-derivate enriched feed further is taken into large-scale approaches thereby benefitting the aquaculture sector.

Effect of Greater Duckweed Spirodela polyrhiza Supplemented Feed on Growth Performance, Digestive Enzymes, Amino and Fatty Acid Profiles, and Expression of Genes Involved in Fatty Acid Biosynthesis of Juvenile Common Carp Cyprinus carpio

The greater duckweed Spirodela polyrhiza (Lemnaceae) is a free-floating freshwater macrophyte. The effect of dietary inclusion of duckweed in the feed of common carp Cyprinus carpio fry was evaluated. The control feed (SP0) contained soybean meal as the primary protein source. In four experimental feeds, greater duckweed was incorporated at levels of 5% (SP5), 10% (SP10), 15% (SP15), and 20% (SP20) replacing soybean meal. Broken-line regression showed that incorporation of greater duckweed at 10 and 13.4% levels were the breakpoint for final weight and specific growth rate (SGR) of fish, respectively. The final weight and SGR of common carp fed diet SP20 were significantly higher compared with those of others. The feed conversion ratio was lowest in SP20 treatment. The inclusion of greater duckweed in the fish feeds showed linear relationships with amylase, trypsin, chymotrypsin, and lipase activities. The content of crude protein was significantly higher in SP10, SP15, and SP20 treatments compared with that of others. Significantly higher crude lipid and ash contents were found in SP20 diet-fed fish compared with other diet-fed fish. The essential amino acids composition was similar in five different diet-fed fish. The greater duckweed supplemented feeds influenced the fatty acid contents of fish. The monounsaturated fatty acids (MUFA) showed an inverse relationship with the inclusion level of greater duckweed in the feed. The highest MUFA content was found in fish fed SP0 diet. The highest level of linoleic acid was found in SP20 diet fed fish. The n-3 PUFA contents of fish showed an increasing trend with the increasing inclusion of greater duckweed, and a significantly higher level was found in SP20 compared with that of others. A significantly higher expression of fas was found in SP5 and fads2d6 in SP5 and SP10 compared with that of others. The expressions of elovl2 and elovl5 were significantly higher in SP5, SP10, and SP15 diet-fed fish compared with other diet-fed fish. The incorporation of greater duckweed in diets improved the growth performance and nutritional value of common carp.

Replacing fish oil and astaxanthin by microalgal sources produced different metabolic responses in juvenile rainbow trout fed 2 types of practical diets.

Dietary fish oil supplementation provides n-3 long-chained polyunsaturated fatty acids for supporting fish growth and metabolism and enriching fillet with eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; c22:6n-3). Two experiments were performed as a 3 × 2 factorial arrangement of dietary treatments for 16 wk to determine effects and mechanisms of replacing 0%, 50%, and 100% fish oil with DHA-rich microalgae in combination with synthetic vs. microalgal source of astaxanthin in plant protein meal (PM)- or fishmeal (FM)- based diets for juvenile rainbow trout (Oncorhynchus mykiss). Fish (22 ± 0.26 g) were stocked at 17/tank and 3 tanks/diet. The 100% fish oil replacement impaired (P < 0.0001) growth performance, dietary protein and energy utilization, body indices, and tissue accumulation of DHA and EPA in both diet series. The impairments were associated (P < 0.05) with upregulation of hepatic gene expression related to growth (ghr1and igf1) and biosynthesis of DHA and EPA (fads6 and evol5) that was more dramatic in the FM than PM diet-fed fish, and more pronounced on tissue EPA than DHA concentrations. The source of astaxanthin exerted interaction effects with the fish oil replacement on several measures including muscle total cholesterol concentrations. In conclusion, replacing fish oil by the DHA-rich microalgae produced more negative metabolic responses than the substitution of synthetic astaxanthin by the microalgal source in juvenile rainbow trout fed 2 types of practical diets.

Plant-Based Diets Induce Transcriptomic Changes in Muscle of Zebrafish and Atlantic Salmon.

With the expansion of the aquaculture industry in the last two decades, there has been a large increase in the use of plant ingredients in aquafeeds, which has created new challenges in fish growth, health and welfare. Fish muscle growth is an important trait that is strongly affected by diet, but our knowledge on the effect of plant protein-based diets on global gene expression in muscle is still scant. The present study evaluated nutrigenomic effects of the inclusion of proteins from pea, soy and wheat into aquafeeds, compared to a control diet with fishmeal as the main protein source using the zebrafish model by RNA-seq; these results were extended to an important aquaculture species by analyzing selected differentially expressed genes identified in the zebrafish model on on-growing Atlantic salmon fed with equivalent plant protein-based diets. Expression of selected Atlantic salmon paralogues of the zebrafish homologs was analyzed using paralogue-specific qPCR assays. Global gene expression changes in muscle of zebrafish fed with plant-based diets were moderate, with the highest changes observed in the soy diet-fed fish, and no change for the pea diet-fed fish compared to the control diet. Among the differentially expressed genes were mylpfb, hsp90aa1.1, col2a1a, and odc1, which are important in regulating muscle growth, maintaining muscle structure and function, and muscle tissue homeostasis. Furthermore, those genes and their paralogues were differentially expressed in Atlantic salmon fed with the equivalent percentage of soy or wheat protein containing diets. Some of these genes were similarly regulated in both species while others showed species-specific regulation. The present study expands our understanding on the molecular effects of plant ingredients in fish muscle. Ultimately, the knowledge gained would be of importance for the improved formulation of sustainable plant-based diets for the aquaculture industry.

The combination of palm and rapeseed oils emerges as a good dietary alternative for optimal growth and balanced lipid accumulation in juvenile gilthead sea bream reared at an elevated temperature

The aquaculture sector needs to develop new tools to optimally increase production for feeding, while facing future environmental changing conditions. One of the major improvements in this industry has been reducing the usage of fishmeal and fish oil (FO) in diet formulations to promote a more sustainable production. In this line and considering global warming, in the present study, juvenile gilthead sea bream were fed a diet with a 60% of FO substitution by vegetable oils (VO) containing mainly palm oil (P) (80% of the VO content) and maintained at 21 or 28 °C. Furthermore, in the condition of elevated temperature, fish were fed with two other diets with the same level of FO substitution and containing either 80% of the VO content of rapeseed oil (R) or an equilibrated combination of both VO (named PR). High temperature induced a significant increase in growth, but a reduction in the hepatosomatic and viscerosomatic indexes, and circulating triglycerides. Otherwise, significant differences were not found among the fish fed the three distinct diets at 28 °C for any of the somatic or plasma parameters analyzed. In the adipose tissue, the higher number of adipocytes of smaller size in fish maintained at 28 °C compared to fish at 21 °C, suggested an activation of adipogenesis despite the gene expression of peroxisome proliferator-activated receptor gamma (pparg) was significantly decreased. Furthermore, lipid droplets of smaller area and downregulation of the fat translocase cd36 and the fatty acid binding protein fabp1 were found in the liver of fish reared at 28 °C compared to those at 21 °C. Concerning differences among dietary groups, fish fed R diet showed in the liver a more extensive surface area occupied by lipid droplets of bigger size, while contrarily, fish fed PR diet had the smallest area filled with smaller lipid droplets. In adipose tissue, PR diet-fed fish had also adipocytes within the smaller size range. These histological data, together with the significant upregulation of several transcription factors (i.e. ppars) and genes related to lipid transport in the two tissues, indicated that the PR diet could be the most equilibrated for gilthead sea bream, to grow at a high rearing temperature while avoiding excessive fat accumulation. Thus, this study highlights the need of fine-tuning the substitution of FO by VO in the elaboration of feeds for this species to assure proper growth and physiological status in a future global warming scenario.

Early feeding with hyperglucidic diet during fry stage exerts long-term positive effects on nutrient metabolism and growth performance in adult tilapia (Oreochromis niloticus)

The present study aimed to investigate nutritional programming of carbohydrate metabolism in Nile tilapia. Early nutritional intervention stimulus was achieved by feeding fry with high-protein/low-carbohydrate (HP/LC) or low-protein/high-carbohydrate (LP/HC) diet since first feeding for 4 weeks, and the effect of nutritional stimulus on carbohydrate and its related metabolism was evaluated through the adult stage. Our findings indicated that at week 1, LP/HC diet-fed fry had lower levels of mRNA for genes coding gluconeogenesis and amino acid catabolism and higher levels of hk2 (P < 0⋅05). As expected, in adult tilapia, although LP/HC diet-fed fish had poorer growth (end of stimulus), the fish showed compensatory growth. There were permanent effects of early high-carbohydrate (HC) intake on several parameters, including (1) modulating hepatic composition, (2) increased muscle glycogen, (3) lower levels of enzymes involved in amino acid catabolism and (4) higher levels of glycolytic enzymes in glycolysis. Finally, HP/LC diet- and LP/HC diet-fed fish were challenged with different dietary carbohydrate levels. Irrespective of challenging diets, the early HC stimulus had significant effects on adult tilapia by (1) promoting utilisation of glucose, which had protein-sparing effects for better growth, (2) inducting lipogenesis and (3) decreasing amino acid catabolism. Taken together, for the first time, we demonstrated that early HC feeding was effective for positive nutritional programming of metabolism in Nile tilapia (an omnivorous fish). It led to the improvement of growth performance in adult fish associated with early feeding, which is linked to a better ability to use glucose, to induce lipogenesis, and to suppress amino acid catabolism.

Histopathological study and intestinal mucous cell responses against Aeromonas hydrophila in Nile tilapia administered with Lactobacillus rhamnosus GG.

Aim:This study aimed to examine the intestinal histopathological lesions and mucous cell responses in the entire intestines of Nile tilapia administered with Lactobacillus rhamnosus GG (LGG)-mixed feed, after Aeromonas hydrophila challenge.Materials and Methods:Intestinal samples from fish fed with control normal diet or LGG-mixed feed (1010 colony-forming unit [CFU]/g feed) with or without A. hydrophila in phosphate-buffered saline challenge (7.46 × 108 CFU/mL/fish) were collected and processed for histopathological study. The mucous cell responses were evaluated using histochemistry, using Alcian blue (AB) at pH 2.5, AB at pH 1.0, and periodic acid-Schiff-AB at pH 2.5. The quantification of the intestinal mucous cell size and the staining character of each mucin type from the entire intestine were recorded and counted.Results:Histopathological study showed remarkable lesions only in the proximal intestine in fish infected with A. hydrophila, while LGG-fed fish had less intestinal damage, perhaps resulting from heterophil infiltration. Furthermore, a significant (p<0.01) increase in mixed mucous cell numbers was observed mainly in the proximal intestine of all challenged fish, compared with normal diet-fed fish without challenge, and also in LGG-fed fish with A. hydrophila challenge compared with LGG-fed fish without challenge.Conclusion:Dietary LGG-fed Nile tilapia showed improvements in host innate immunity. In addition, LGG was effective in decreasing intestinal lesions from A. hydrophila-induced intestinal damage. Moreover, increasing numbers of mixed mucous cells in the proximal intestine might be indicative of certain pathological conditions in Nile tilapia after A. hydrophila infection.

High-carbohydrate diet promotes the adaptation to acute hypoxia in zebrafish.

Oxygen deprivation (hypoxia) is a common challenge in water environment, which causes lack of energy and oxidative damage in organisms. Many studies have indicated a number of physiological and metabolic changes under hypoxia, but the effects of dietary nutrients on hypoxia tolerance have not been well evaluated. In the present 7-week feeding trial, we fed zebrafish with low-protein diet (LP), high-protein diet (HP), low-fat diet (LF), high-fat diet (HF), low-carbohydrate diet (LC), and high-carbohydrate diet (HC), respectively. Afterward, the resistance to acute hypoxia challenge, growth, body composition, activities of metabolic enzymes, and expressions of energy homeostasis-related genes and six hifαs genes were measured. The results indicated that only the HC diet could significantly improve the resistance to hypoxia challenge. Moreover, the HC diet feeding caused higher glycogen deposition in the liver and muscle, and these glycogens were significantly reduced after 6-h acute hypoxia challenge. Meanwhile, the lactate content in the liver and blood was increased in the HC groups. At hypoxia status, the relative mRNA expressions of the genes related to glycolysis, ATP production, insulin signaling pathway, and hif-3a (hif1al) were all significantly increased in the muscle of the HC diet-fed fish. This study revealed that high-carbohydrate diet could improve the resistance to hypoxia by activating glycolysis and hif/insulin signaling pathway in zebrafish, mainly in the muscle, to efficiently supply energy. Therefore, our results highlight the importance of dietary carbohydrate in resisting hypoxia in fish.

Effect of dietary Citrus sinensis peel extract on growth performance, digestive enzyme activity, muscle biochemical composition, and metabolic enzyme status of the freshwater fish, Catla catla

BackgroundThe present study was made to assess the effects of dietary Citrus sinensis peel extract on the growth performance, digestive enzyme activity, muscle biochemical compositions, profiles of fatty acid and amino acid, and metabolic enzyme status of the freshwater fish Catla catla. The methanolic extract of C. sinensis peel was supplemented with basal diets at 2, 6, and 10 g kg−1 and fed to C. catla for a 45-day experiment period.ResultsFish fed with the different concentrations of C. sinensis peel-supplemented extract showed significant (P ˂ 0.05) improvement in the survival, growth, muscle biochemical compositions, digestive enzyme activities, and profile of amino acids and fatty acids when compared to control. Among these different concentrations, 6 g kg− 1C. sinensis-supplemented diet produced a significantly better performance when compared to other concentrations. Similarly, the insignificant (P > 0.05) difference was observed in the metabolic enzyme activities (glutamic oxaloacetic transaminase and glutamic pyruvic transaminase) in all concentrations of C. sinensis peel-supplemented diet-fed fish. It indicates that the supplemented peel extract did not produce any adverse effect on C. catla.ConclusionThe obtained results suggested that the 6 g kg− 1 of C. sinensis can be supplemented in the diet of C. catla for regulating better survival and growth.

Achyranthes aspera (Prickly chaff flower) leaves- and seeds-supplemented diets regulate growth, innate immunity, and oxidative stress in Aeromonas hydrophila-challenged Labeo rohita

ABSTRACT The immunostimulatory and disease-resistance properties of Achyranthes aspera were evaluated in rohu (Labeo rohita) challenged with Aeromonas hydrophila. Experimental diets were enriched with leaves at 0.25% (D1) and 0.5% (D2) and seeds at 0.5% (D3); the control diet (D4) was without any enrichment. Rohu (2.02 ± 0.23 g) were cultured for 75 days and then challenged with bacteria. The highest average weight was observed in the D3 diet-fed fish. The cumulative mortality rates were 70%, 60%, 40%, and 30% in the D4, D1, D2, and D3 diets fed to rohu respectively. Enriched diets significantly increased myeloperoxidase, nitric oxide synthase, and serum lysozyme levels and decreased malondialdehyde and carbonyl protein content. Expressions of lysozyme C and lysozyme G were significantly (P < .05) higher in the D3 diet-fed fish. In the kidney, IL-1β and TLR 4 were up-regulated in enriched-diet-fed fish. Supplementation of seeds and leaves at 0.5% showed a positive impact in fish.

Effects of natural feeding stimulants and glutamic acid supplementation on the feed intake, growth performance and digestive enzyme activities of red sea bream ( Pagrus major ) fed fish meal‐free soy protein concentrate (SPC)‐based diet

Two experiments were conducted for red sea bream (Pagrus major). In experiment 1, the optimum level of glutamic acid and natural feeding stimulants to enhance feed intake were determined and found that glutamic acid level of 0.5% and fish meat hydrolysate (FMH) were effective. In experiment 2, fish were fed with soy protein concentrate (SPC)-based diet with synthetic feeding stimulants (Basal diet), the Basal diet with FMH (FMH diet), the FMH diet with glutamic acid (FMHG diet) and with fish meal diet (FM diet) as a control until satiation for 8 weeks. Feed intake of FMHG-fed fish was significantly higher than others (p < 0.05). Specific growth rate and the feed conversion ratio of FMHG were comparable to those of FM-fed fish (p > 0.05). Relative visceral fat ratio and crude lipid content of any SPC-based diet-fed fish tended to be lower than those of FM diet-fed fish. There were no significant differences in trypsin and lipase activities hepatopancreas among treatments. SPC can be utilized as a sole protein source in a diet for red sea bream. The lower growth performance in SPC-based diet- fed fish was not due to poor digestive enzyme secretion but could be associated with lipid utilization disorder.

Intestinal microbiome and its potential functions in bighead carp (Aristichthys nobilis) under different feeding strategies.

Bighead carps (Aristichthys nobilis) were divided into four groups with different feeding strategies: group A, nature live food only (fertiliser only, 200 g urea + 160 g ethylamine phosphate + 250 g Huangjintai bio-fertiliser); group B, nature live food + 1/2 formulated feed; group C, nature live food + formulated feed; and group D, formulated feed only. The intestinal microbiomes of the different groups were compared through the Illumina MiSeq sequencing of the bacterial 16S rRNA gene. The specific growth rate (SGR), survival and blood biochemical factors of the fish were also investigated. Results showed that feeding treatment influenced the intestinal communities in the fish. In specific, more bacterial phyla dominated in groups A and B (phyla Bacteroidetes, Fusobacteria, Firmicutes and Proteobacteria in group A, phyla Proteobacteria and Fusobacteria in group B) than in groups C and D (phylum Proteobacteria). The diversity was also lower in groups C and D than in groups A and B. Unweighted pair-group method analysis revealed a clear difference in intestinal microbiota among the different feeding treatments. No difference in survival rate was found among the treatment groups, but the SGR was significantly higher (P < 0.01) in groups B, C and D than in group A. Functional analysis showed that the intestinal bacteria correlated with fish glucose metabolism in group A but with lipid metabolic activity in groups B, C and D. In summary, the intestinal microbiomes and their potential functions vary in bighead carp under different feeding treatments. This study provides new insights into the gut microbiomes of filter-feeding and formulated diet-fed fish.

Effects of alcohol extract of defatted soybean meal on growth performance and digestive physiology of yellowtail Seriola quinqueradiata

The effects of alcohol extract of soybean meal on growth performance, digestibility, and pancreatic enzyme and bile acid status of yellowtail Seriola quinqueradiata were studied. Fish were fed one of the following for 8 weeks: a fish meal (FM) control diet (FMD), a defatted soybean meal diet (SBMD), an alcohol-extracted SBM diet (ExSBMD), an ExSBMD with alcohol-extract diet (ExSBM + ExtD), and an FMD with alcohol-extract diet (FM + ExtD). Growth performance was significantly inferior in fish fed with SBM, ExSBM + ExtD, and FM + ExtD compared to FMD- or ExSBMD-fed fish. Total bile acid levels, and trypsin and lipase activities in the anterior intestine were significantly lower in fish fed with SBM, ExSBM + ExtD, and FM + ExtD than in fish fed with ExSBMD and FMD, despite similar values in gallbladder or pyloric caeca. Cholecystokinin mRNA levels of the former diet-fed fish were significantly lower than those of FMD- or ExSBMD-fed fish. Lipid and protein digestibility of fish fed with SBMD, ExSBM + ExtD, and FM + ExtD was significantly reduced in comparison with that of fish fed with FMD or ExSBMD. These findings indicate that the alcohol extract of soybean meal inhibited the secretion of bile acids and pancreatic enzymes by a decrease of cholecystokinin stimulation. This inhibition seemed to be responsible for a low growth performance through impairment of the assimilation of lipid and protein.

β-1,3/1,6-Glucan-supplemented diets antagonize immune inhibitory effects of hypoxia and enhance the immune response to a model vaccine

The diets of farmed salmon are usually supplemented with immunostimulants to improve health status. Because β-glucan is one of the most common immunostimulants used in diets, here we examined the effect of two β-1,3/1,6-glucan-supplemented diets on the expression of immune response genes of Atlantic salmon. The relative abundances of IFN-α1, Mx, IFN-γ, IL-12, TGF-β1, IL-10, and CD4 transcripts were evaluated in head kidney by qRT-PCR. We assessed the effects of the diets under normoxia and acute hypoxia, as salmon are especially sensitive to changes in the concentration of dissolved oxygen, which can also affect immunity. These effects were also tested on vaccinated fish, as we expected that β-1,3/1,6-glucan-supplemented diets would enhance the adaptive immune response to the vaccine. We found that administration of the Bg diet (containing β-1,3/1,6-glucan) under normoxia had no effects on the expression of the analyzed genes in the kidney of the diet-fed fish, but under hypoxia/re-oxygenation (90 min of acute hypoxia), the βg diet affected the expression of the antiviral genes, IFN-α1 and Mx, preventing their decrease caused by hypoxia. The Bax diet, which in addition to β-1,3/1,6-glucan, contained astaxanthin, increased IL-12 and IFN-γ in kidneys. With fish exposed to hypoxia/reoxygenation, the diet prevented the decrease of IFN-α1 and Mx levels observed after hypoxia. When fish were vaccinated, only the levels of IL-12 and CD4 transcripts increased, but interestingly if fish were also fed the Bax diet, the vaccination induced a significant increase in all the analyzed transcripts. Finally, when vaccinated fish were exposed to hypoxia, the effect of the Bax diet was greatly reduced for all genes tested and moreover, inducible effects completely disappeared for IL-12, IFN-α, and Mx. Altogether, these results showed that the tested β-1,3/1,6-glucan diets increased the levels of transcripts of key genes involved in innate and adaptive immune response of salmon, potentiating the response to a model vaccine and also antagonizing the effects of hypoxia.