Dietary amino acid profile affects muscle cellularity,growth, survival and ammonia excretion of meagre (Argyrosomus regius) larvae

Formulation of diets according to fish amino acid (AA) qualitative requirements may improve fish growth. Two diets with different AA profiles were tested on 16‐day‐old meagre during 20 days. The first diet had an AA profile closer to meagre larval AA requirements (BAL), whereas the second had a different AA profile (UNBAL). Results showed that larvae fed the diet with higher similarities to the AA profile of meagre carcass had a higher final weight (19.8 ± 0.5 mg versus 13.4 ± 1.8 mg) and lower ammonia excretion after being fed (0.6 ± 0.1 ml/(g DW. larvae. h) and 0.8 ± 0.1 ml/(g DW larvae. h)). A higher mean fibre area was obtained in 36 DAH larvae fed the BAL diet (224.8 ± 33.3 μm² versus 158.8 ± 34.5 μm²) as well as higher larval weight. When fibre area distribution was analysed, a higher frequency of larger fibres was observed in 36 DAH BAL larvae, suggesting that fibre hypertrophy had a higher importance in this treatment. In conclusion, this study shows that meagre larvae fed a diet with an AA profile closer to their requirements had lower nitrogen losses and higher final weight, as result of higher muscle hypertrophy.     

Effect of increased dietary protein level in meagre (Argyrosomus regius) juvenile growth and muscle cellularity

In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm² and 2,200 μm² between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels.     

Evaluation of immune response and performance of silver catfish fed functional linseed fibres in response to hypoxia stress

This study was conducted to evaluate the immunostimulating activity and growth promoting of diets supplemented with different rations of soluble and insoluble linseed fibre to Rhamdia quelen under hypoxia‐induced acute stress. For this reason, soluble and insoluble fractions of linseed fibre were concentrated separately and combined into four ratios (1:0.5; 1:1; 1:2 and 1:4), which were added to the diets of silver catfish (6.43 ± 0.12 g) and evaluated in a biological assay, along with a control diet (without addition of linseed fibre). After being fed the experimental diets for 45 days, specimens of silver catfish were submitted to hypoxia‐induced acute stress. They were kept out of water for 60 s. Immediately afterwards, blood and cutaneous mucus were collected for subsequent determination of immunological indicators and stress. After stress, the fish were weighed and measured for performance parameter calculation. The experimental design was completely randomized with five treatments and four replications. The data underwent analysis of variance and the means were compared by Tukey's test (p < .05). The fish fed diets containing the 1:2 and 1:4 soluble:insoluble fibre ratios, showed higher total protein content, globulin, plasma alkaline phosphatase activity, and performance in addition to higher mucoprotein content in the cutaneous mucus of the fish. Regardless of their ratio in the diet, linseed fibre provided higher plasma levels of total immunoglobulins and reduction in cortisol levels. The 1:1, 1:2 and 1:4 diets led to higher levels of total immunoglobulins and alkaline phosphatase activity in cutaneous mucus. The results indicate that linseed fibre has a stress‐ reduction, immunostimulant and a growth promoter effect on silver catfish. The 1:2 or 1:4 soluble: insoluble fibre ratios provided greater stimulation of the target immunological indicators and performance.     

Effect of replacing dietary fish oil with soybean oil on growth performance,fatty acid composition and haematological parameters of juvenile meagre,Argyrosomus regius

A nutrition trial with meagre, Argyrosomus regius was assessed to determine the effect of dietary replacement of fish oil (FO) by soybean oil (SO) on the growth, feed utilization, body composition, fatty acid composition and basic haematological parameters. Six isonitrogenous (47% crude protein) and isoenergetic (gross energy 22 kJ/g) experimental diets were formulated by replacing 0 (FO), 20 (S20), 40 (S40), 60 (S60), 80 (S80) and 100 (S100) % of the FO with SO. Fish were fed three times daily to near satiation for 14 weeks. The specific growth rate (SGR) of fish fed S100 diet was significantly lower than the other treatments, except SO80 diet. The fish fed SO100 diet displayed significantly higher feed conversion ratio than that of other diets (P < 0.05). It was observed that fish fed the SO100 and SO80 diets displayed haemoglobin (HGB) levels significantly lower (P < 0.05) than fish fed the SO20 diet. Packed cell volume (PCV) of fish fed SO20 diet was significantly higher compared to SO100. The white blood cell (WBC) and red blood cell (RBC) remained unaffected by dietary treatment. The docosahexaenoic acid (22:6n‐3, DHA) and eicosapentaenoic acid (20:5n‐3, EPA) levels of meagre were significantly reduced by the substituting of dietary SO by FO at the end of the feeding period. The level of linoleic acid (18:2n‐6, LA) and linolenic acid (18:3n‐3, LNA) significantly raised in fish fed with SO diets (P < 0.05). The results of this study showed that SO could be replaced FO up to 80% in meagre diet without negative effect on growth performance and basic haematological parameters. Furthermore, the maximum level of FO replacement with SO determined by second order polynomial regression analysis, was 30.1% on the basis of maximum SGR.     

Stress and metabolic indicators in a relatively high (European sea bass,Dicentrarchus labrax) and a low (meagre,Argyrosomus regius) cortisol responsive species,in different water temperatures

The aim of this study was to examine species‐specific differences in pre‐ and post‐stress concentrations of haematological, metabolic and hormonal parameters in two Mediterranean fish species, one with relatively high (European sea bass, Dicentrarchus labrax) and the other with low (meagre, Argyrosomus regius) basal and post‐stress blood cortisol concentrations, in relation to different water temperatures. Fish were reared in net‐pen sea cages and exposed to an identical acute stressor (crowding and chasing with a net for 5 min) in three different periods of the year. Results indicated that inter‐specific differences occurred in most of the examined parameters. In addition, within each species, differences between sampling periods existed in plasma cortisol, glucose, osmolarity, blood pH and muscle glycogen concentration. Glucose, lactate and osmotic pressure showed a constant pattern of change, with maxima at half an hour post stress in both species, while cortisol, and blood and muscle pH, were significantly altered only in E. sea bass. No alterations were observed in liver and muscle glycogen concentrations in E. sea bass, while a significant reduction was evident only in the coldest temperature in meagre. It is concluded that there are important species‐specific differences in the magnitude of hormonal and metabolic response to acute stress and that both basal and post‐stress blood cortisol concentrations are affected by the sampling period.     

Dietary profile of n‐3 series LC‐PUFAs in rainbow trout under regular stripping condition: Semen production and quality,hepato‐somatic index,haemato‐immunologic values,oxidative stress and fatty acid composition of liver,muscle and semen

In this study, the semen production and quality, hepato‐somatic index, haemato‐immunologic values, oxidative stress and the fatty acid contents in liver, muscle and semen of rainbow trout fed diets supplemented n‐3 series long‐chain polyunsaturated fatty acids (LC‐PUFAs) under regular stripping condition were investigated. For this aim, three diets (Control, D1 and D2) were prepared. These diets were contained n‐3 LC‐PUFAs (as a percentage of dietary total fatty acid) at 3.14%, 7.84% and 13.63% respectively. Experimental fish were fed with the control and test diets. The highest hepato‐somatic index, spermatologic (semen pH and volume, sperm motility and density), haematologic (haematocrit value, haemoglobin, erythrocyte count, corpuscular volume, haemoglobin and its concentration in corpuscular), immunologic (nitroblue tetrazolium activity, leucocyte count, phagocytic index, protein and immunoglobulin [IgM] in total plasma) and antioxidants (reduced glutathione, catalase, glutathione peroxidase and superoxide dismutase) values were found in fish fed the D2, D1 and control diets respectively (p < 0.01). Increase in the dietary n‐3 LC‐PUFAs was not significantly (p > 0.01) increased the oxidative stress (malondialdehyde) in fish. The results indicated that the n‐3 LC‐PUFAs at 13.63% level of total fatty acid in the diet could increase the semen production and quality, hepato‐somatic index, haematologic and immunologic values, and the n‐3 LC‐PUFA contents in liver, muscle and semen of rainbow trout broodstock under regular stripping condition.     

Digestive enzyme activity and nutrient digestibility in meagre (Argyrosomus regius) fed increasing levels of black soldier fly meal (Hermetia illucens)

The effect of partially replacing fishmeal (FM) by black soldier fly larvae meal (Hermetia meal—HM) in meagre (Argyrosomus regius) diet was evaluated for nutrient digestibility and digestive enzyme activity. For that purpose, triplicate groups of fish (18.0 ± 0.02 g) were fed during 48 days either a control diet (CTR), without HM, or one of three diets including 100, 200 and 300 g/kg of HM, replacing 17, 35 and 52% of FM, respectively. Apparent digestibility coefficients (ADCs) of dry matter, energy, protein, lysine, isoleucine, leucine, phenylalanine, alanine, glutamate, glycine and serine presented a decreasing response with increased HM inclusion. Chitin ADC was null, independent of dietary HM inclusion. Total alkaline protease activity increased while trypsin activity decreased with dietary HM inclusion. No intestinal chitinolytic activity was detected. Intestinal alkaline protease zymogram revealed nine bands with proteolytic activity against casein, with molecular weights ranging between 15 and 75 kDa. Anti‐protease activity in the intestine was not affected by dietary inclusion of HM compared to the CTR diet. Overall, it is concluded that replacement of up to 17% FM with HM (100 g/kg HM inclusion level) in meagre diets has no major adverse effects in diet digestibility and digestive enzyme activity.     

Effect of L‐tryptophan supplemented diets on serotonergic system and plasma cortisol in Totoaba macdonaldi (Gilbert, 1890) juvenile exposed to acute stress by handling and hypoxia

Brain serotonin and cortisol play a central role in integrating the neuroendocrine response to stress. Previous studies in aquatic species show that dietary supplementation with the 5‐HT precursor L‐tryptophan amino acid is able to modulate this response. The aim of this study was to evaluate the effect of dietary tryptophan (Trp) on the serotonergic system and acute stress response in Totoaba macdonaldi. Four groups of fish were fed with one of four isonitrogenous and isocaloric diets formulated with different Trp content: 0.5% (1X TRP, control diet), 1.1% (2X TRP), 1.7% (3X TRP) and 2.3% (4X TRP). After a feeding period of 21 days, groups were exposed to acute stress by handling with a net or hypoxia. Feeding with Trp‐enriched diets resulted in increased 5‐HT content in telencephalon of undisturbed fish. Handling increased the 5‐hydroxyindole acetic acid (5‐HIAA) and serotonin turnover (5‐HIAA/5‐HT) in telencephalon of fish fed with 1X TRP and 2X TRP but was not significant for the fish fed 3X TRP and 4X TRP, and no significant increase was observed by hypoxia in both telencephalon and hypothalamus in any of the diets. An inverted U‐shaped response was observed in plasma cortisol increasing with 2X TRP after both handling and hypoxia and decreasing with diets rich in Trp, 3X TRP and 4X TRP. A higher increase was observed in haematocrit, plasma glucose and lactate in hypoxia than the handling groups. Our results indicate that Trp supplementation modulated cortisol response and mediated negative feedback of 5‐HT system in telencephalon after acute stress.     

Assessing the feasibility of using pomegranate (Punica granatum) seed oil,rich in conjugated linolenic acid,as a lipid source in the diet of common carp,Cyprinus carpio,juveniles

In this study, the feasibility of using pomegranate seed oil, rich in conjugated linolenic acid and its partial replacement for fish oil in fish diet were investigated. Common carp, Cyprinus carpio, juveniles (1.8 ± 0.1 g) were fed four isonitrogenous and isolipidic diets with similar basal composition but different oil mixture containing 100% fish oil (A), 50% fish oil +50% sunflower oil (B), 50% fish oil +25% sunflower oil +25% pomegranate seed oil (C) and 50% fish oil +50% pomegranate seed oil (D) for 8 weeks. The highest weight gain was observed in fish fed diet D (p < 0.05). Test diets had no significant effect (p > 0.05) on saturated and monounsaturated fatty acid contents of fish muscle. Docosahexaenoic acid (22:6n‐3; DHA) was significantly lower in the muscle of fish fed diet B (p < 0.05) compared to those fed diet A. However, there was no significant difference in the muscle DHA content of fish fed diets A, C, or D. No specific hepatocyte damage associated to dietary pomegranate seed oil was found in this study. This study showed a 50‐50 combination of fish oil and pomegranate seed oil could be used as dietary lipid source for common carp without any adverse effect on growth performance or muscle n‐3 content while accumulated punicic acid in the muscle could be considered as added value for the final human consumer.     

Digestibility,growth and pigmentation of astaxanthin,canthaxanthin or lutein diets in Lake Kurumoi rainbowfish,Melanotaenia parva (Allen) cultured species

New cultured ornamental fish namely Lake Kurumoi rainbowfish Melanotaenia parva (Allen) run into reduced of colour performances when reared in the aquaria, consequently, fish feed must be added with carotenoids as a pigment source. The aim of this study was to evaluate the digestibility, growth and pigmentation of astaxanthin, canthaxanthin and lutein in diet. Apparent digestibility coefficients (ADC) of dry matter, lipid, protein, carotenoids, growth and pigmentation were studied in twenty fish after 14 and 56 days of observation. The single‐dose supplementation of 100 mg/kg of astaxanthin, canthaxanthin, or lutein diets on fish was fed by apparent satiation. The basal diet without carotenoids was used as control. The result showed that the ADC of carotenoids of test diets was higher compared to control. Fish fed astaxanthin diet had higher survival rate (96.67 ± 2.89%), colour measurements of lightness (57.60 ± 7.46%), a*‐values (4.66 ± 1.20), total carotenoids content in skin (33.75 ± 5.02 mg/kg) and muscle (2.16 ± 0.74 mg/kg). Astaxanthin also increased the growth after 14 days (2.00% ± 0.19%/days) but there was no significantly different at the end of experiment. The yellowish‐orange colour performance was more rapidly achieved by fish fed astaxanthin diet after 28 days experimentation. These values suggested that dietary carotenoids were required and astaxanthin diet was superior to other diets for skin pigmentation of Lake Kurumoi rainbowfish.     

Effects of dietary chlorogenic acid on growth,flesh quality and serum biochemical indices of grass carp (Ctenopharyngodon idella)

The study was to investigate effects of dietary chlorogenic acid (CGA) on growth performance, flesh quality and serum biochemical indices of grass carp (95.1 ± 0.3 g) (Ctenopharyngodon idella) fed seven different diets, including control diet, Eucommia ulmoides (EU)‐supplemented diet (20 g kg^–1) and CGA‐supplemented diets containing 100, 200, 400, 600 and 800 mg/kg CGA. Contents of collagen and alkaline‐insoluble collagen in muscle and skin were significantly increased by dietary CGA and EU (p < .05). Total essential amino acids (TEAA) and total amino acids (TAA) in muscle of grass carp fed EU diet or 400, 600 and 800 mg/kg CGA diet were significantly higher than those of fish fed control diet and 100 and 200 mg/kg CGA diet (p < .05). Fish fed 200–800 mg/kg CGA showed significantly lower muscle crude lipid content than EU, control and 100 mg/kg CGA groups (p < .05). Fish fed CGA‐supplemented diets (100–800 mg/kg) had significantly higher muscle fibre density and lower muscle fibre diameter than control group (p < .05). In conclusion, supplementation of CGA improved flesh quality of grass carp, and supplemental level of CGA for improving flesh quality and growth was estimated to be 400 mg/kg diet.     

Effects of phospholipid addition to diets with different inclusion levels of fish oil on growth and fatty acid body composition of juvenile swimming crab Portunus trituberculatus

Six experimental diets were designed with two phospholipid (PL; 0% and 1.5%) and three fish oil levels (0%, 1% and 3%) to evaluate the effects of dietary fish oil and PL levels on growth, survival and fatty acid composition of juvenile swimming crab, Portunus trituberculatus. Diets were iso‐energetic and iso‐nitrogenous and each diet was fed to triplicate groups (initially weight, 24.88 ± 0.04 g per crab) for 59 days. Weight gain (WG) and specific growth rate (SGR) increased with dietary PL addition to 0% fish oil‐supplemented diets (P < 0.05). On the other hand, WG and SGR decreased with dietary PL addition to 3% fish oil diets (P < 0.05). Crabs fed PL supplemented diets had higher haemolymph low‐density lipoprotein cholesterol concentrations and muscle crude lipid levels (P < 0.05) than crabs fed a none PL supplemented diet. The percentage of highly unsaturated fatty acids (HUFA; % total FA) in both polar and neutral lipids fractions of muscle tissue only increased in case of PL addition to 0% and 1% fish oil‐supplemented diets (P < 0.05). HUFA levels in the neutral lipids fraction of the hepatopancreas increased by dietary PL addition at each dietary fish oil level (P < 0.05). In this study, both dietary fish oil and PL addition contributed to a high n‐3/n‐6 ratio in muscle and hepatopancreas of P. trituberculatus. In conclusion, PL addition is only meaningful with fish oil‐deficient diets, in which case it enhanced lipid transport and HUFA absorption efficiency, hence improving the nutritional value of the diet.     

Immunomodulatory Effects of Dietary β‐glucan and Vitamin C in Nile Tilapia,Oreochromis niloticus L., Subjected to Cold‐induced Stress or Bacterial Challenge

To determine the dietary β‐glucan and vitamin C levels that would enable the fish to cope with different stress, 252 tilapia (16.86 ± 0.24 g) were distributed in thirty six 250‐L aquaria and fed experimental diets for 60 d. Diets were supplemented with β‐glucan (0.1, 0.2, 0.4, and 0.8%) and vitamin C (400 and 600 mg/kg diet) and distributed in a factorial design that included a control diet (0 β‐glucan/125 mg vitamin C/kg). After growth performance analyses, a group of 108 fish were subjected to cold‐induced stress and another to Aeromonas hydrophila infection. Hematological and immunological parameters were determined before and after the stress. Growth performance was not affected. Red blood cells, hematocrit, mean corpuscular volume, total plasma protein, albumin : globulin ratio and leukocytes, lymphocytes, neutrophils, and monocytes were affected (P < 0.05) by stress and/or diets. The control diet resulted in higher post‐infection cortisol (P < 0.05). Liver vitamin C was directly proportional to dietary vitamin C (P < 0.05). The production of hydrogen peroxide and nitric oxide was also affected by diets and/or bacterial challenge (P < 0.05). In total, 0.1–0.2% β‐glucan and 600 mg/kg vitamin C increased fish resistance to stress and 0.8% β‐glucan resulted in reduced immune responses regardless of the vitamin C supplementation level.     

Total substitution of fish oil by vegetable oils in Senegalese sole (Solea senegalensis) diets: effects on fish performance, biochemical composition, and expression of some glucocorticoid receptor-related genes

To study the substitution of fish oil by vegetable oils in fish diets, juveniles Senegalese sole (Solea senegalensis) were fed diets (56 % crude protein, 12 % crude lipid) containing either linseed (100LO) or soybean (100SO) oils in comparison with a 100 % fish oil-based diet (100FO) for 90 days. Samples of muscle, liver, and intestine were collected for biochemical analysis and for glucocorticoid receptor-related genes, including GR1 and GR2, and the associated heat shock proteins HSP70, HSP90AA, and HSP90AB. Besides, basal levels of plasma cortisol were also determined. After the feeding period, a stress test, consisting on 5 min of net chasing, was applied to a selected population of each dietary group. Total replacement of fish oil by vegetable oils did not induced changes in fish growth and performance, but affected fatty acid profile of muscle, liver, and intestine, reflecting those tissues the characteristic fatty acids of each type of dietary oil. A tendency to conserve the ARA/EPA ratio could be observed in the different tissues, despite of the level of these fatty acids in diet. Chasing stress induced an increase of muscle GR1 and a reduction in intestinal GR2 relative expressions at any of the experimental diets assayed. In liver, chasing stress induced an increase in both GR1 and GR2 gene expression in fish fed fish oil diets. Similarly, chasing stress induced an increase of muscle HSP70 and decrease of HSP90AB in liver at any of the experimental diet assayed. Besides, vegetable oils decreased the expression of HSP70 in intestine, being the relative expression of liver HSP90AA increased by the inclusion of linseed oil in the diet, at any of the experimental conditions assayed.     

Juvenile Atlantic salmon decrease white trunk muscle IGF‐1 expression and reduce muscle and plasma free sulphur amino acids when methionine availability is low while liver sulphur metabolites mostly is unaffected by treatment

We previously reported that juvenile Atlantic salmon with mean initial BW 11.5 g offed a methionine deficient diet had lower weight gain due to a reduced protein accretion, while lipid gain was unaffected. Muscle of the fish fed the methionine deficient diet was depleted for sulphur amino acids, while in liver, the concentration of these metabolites was maintained within narrow limits. We speculated whether this could be due to an increased muscle proteolysis to support a prioritized liver metabolism in fish fed the low methionine diets. In this study, we assessed whether genes associated with muscle proteolysis increased under methionine deficiency. The composition of the diets was similar to those used previously containing 1.6 or 2.1 g Met/16 g N. We confirmed that the fish fed the low methionine diet gained less protein compared to fish fed the DL‐methionine enriched diet (P = 0.014), but growth did not reduce significantly. Also the deficient fish maintained the concentrations of liver sulphur amino acids and reduced muscle free methionine. Several of the other free amino acids within muscle increased. Further, methylation capacity was maintained in liver but reduced in the muscle (P = 0.78 and 0.04, respectively). Gene expression of muscle IGF‐1 was lower (P = 0.008) and myosin light chain 2 tended (MLC2, P = 0.06) to be reduced in fish fed low methionine diet, concurrently the activity of cathepsins B+L increased (P = 0.047) in muscle of fish fed the low methionine diet. Gene expression of the muscle‐specific E3 ubiquitine ligases (Murf and MaFbx) was not affected by treatment. Thus, the lower protein gain observed in fish fed the low methionine diet may be caused by reduced protein synthesis in line with the reduced IGF‐1 gene expression in the white trunk muscle. Thus, to support metabolism, the dietary protein needs to be balanced in amino acids to support metabolism in all compartments of the body and secure maximal protein gain.     

Growth response,body composition,plasma metabolites,digestive and antioxidant enzymes activities of Siberian sturgeon (Acipenser baerii,Brandt, 1869) fed different dietary protein and carbohydrate: lipid ratio

Knowing the effect of dietary nutrients on physiological parameters, especially oxidative stress, during fish rearing can be useful to improve fish health and optimize production in aquaculture. In this study, four iso‐energetic (2 × 2 factorial design) diets differing in nutrient composition were submitted to the Siberian sturgeon juveniles, to analyse biochemical and physiological responses. The juveniles were fed for as long as 10 weeks with the following diets: low protein–high carbohydrate (CHO): lipid ratio (LP‐St), high protein–high CHO: Lipid ratio (HP‐St), low protein‐low CHO: Lipid ratio (LP‐L) and high protein‐low CHO: Lipid ratio (HP‐L). It was shown that HP‐L diet significantly induced higher growth performance in the juveniles than LP‐L; however, there was not a significant difference between them with other treatments. HSI was increased by higher dietary CHO: L ratio. The result obviously showed the higher dietary fat led to an increase in sturgeon body fat content. In addition, dietary protein and CHO: lipid ratio significantly affected plasma metabolites (glucose, cortisol, cholesterol and triglyceride) but did not affect IGF‐1 and insulin levels. Based on enzyme activities results, incorporation of high protein (44%) in the diet induced lower amylase activity and carbohydrate digestion in the sturgeon juveniles. Moreover, antioxidant enzyme activities in this species were more influenced by lipid than other nutrients. In conclusion, using appropriate carbohydrates (~30%) in the sturgeon diet helps to spare protein. Furthermore, it is suggested to decrease the amount of lipid in high protein diet, to improve higher sturgeon fillet quality and less oxidative damage in liver.     

Effects of antimicrobial peptide APSH‐07 on the growth performance,anti‐oxidation responses,stress resistance and intestine microbiota in large yellow croaker Larimichthys crocea

A 65‐day feeding trial was conducted to investigate the effects of dietary antimicrobial peptide APSH‐07 on the growth performance, anti‐oxidation responses, stress resistance and intestine microbiota of large yellow croaker Larimichthys crocea. Four isonitrogenous and isolipidic diets were formulated with 0, 30, 60 and 90 mg/kg of APSH‐07, respectively. The results showed that the fish fed with 90 mg/kg of dietary APSH‐07 had the significantly highest specific growth rate (p < .05). The activities of catalase, superoxide dismutase, the total anti‐oxidative capacity and lysozyme had the significantly highest values in liver of fish fed with 90 mg/kg of dietary APSH‐07 (p < .05). Serum glucose increased significantly in fish fed diets without APSH‐07 supplementation after temperature stress, while serum cortisol increased significantly in those after trawl stress (p < .05). Fish fed with 90 mg/kg of dietary APSH‐07 showed significantly higher operational taxonomic units, ACE estimator and phylogenetic diversity whole tree in intestine microbiota compared to fish fed without APSH‐07 (p < .05). In conclusion, under the present experimental condition, 90 mg/kg of antimicrobial peptide APSH‐07 supplementation in diet had the better growth performance, higher anti‐oxidation and stress resistance capacity, and a potentially more beneficial intestine microbial community of large yellow croaker.     

Effect of dietary canthaxanthin on the growth and lipid composition of red porgy (Pagrus pagrus)

A 24‐week feeding trial was conducted to study the possible effect of dietary canthaxanthin on red porgy growth and lipid composition. Two triplicate groups were established to test two experimental diets: (1) Control group fed a diet with no added carotenoids, and (2) canthaxanthin group (CTX100) fed a diet with 100 mg of synthetic canthaxanthin per kilogram of diet (CTX). Final and eviscerated weight were increased (P < 0.05) in the CTX100 treatment. The rest of growth performance parameters were not affected by the CTX diet. Whole‐fish total lipid content was decreased (P < 0.05) in CTX100 fish. In the liver, total lipids were not affected; however, saturated fatty acids in CTX100 treatment were significantly lower together with a higher n‐3 PUFA and a lower n‐6 PUFA, therefore increasing the n‐3/n‐6 ratio. Liver histology of CTX100 fish revealed decreased lipid vacuolization thus, significantly lowering hepatocyte area. In the muscle, total lipids were not affected. Similar to the liver, an increase of n‐3 PUFA and decrease n‐6 PUFA, led to a significant increase of the n‐3/n‐6 ratio. Concerning plasma, only total cholesterol (TC) was significantly affected by the CTX diet. Dietary canthaxanthin has an effect on red porgy lipid composition.     

Fish protein hydrolysate in diets of turbot affects muscle fibre morphometry,and the expression of muscle growth‐related genes

The study was conducted to investigate the effects of fish protein hydrolysate (FPH) in diets for turbot on growth performance, muscle fibre morphometry, and the expression of muscle growth‐related genes. A control diet (FPH0) contained 0 g/kg FPH, and four experimental diets were formulated replacing fishmeal with FPH at levels of 45 (FPH4.5), 120 (FPH12), 180 (FPH18) and 300 (FPH30) g/kg. Fish fed the FPH12 and FPH18 diets had higher specific growth rate (SGR) than fish fed the FPH0 diet (p < .05), and a quadratic regression was found between SGR and dietary FPH level (p = .001, R² = .677). Cross‐section area (CSA) and the length of sarcomere in the FPH12 group increased compared with the control group (p < .05), and a quadratic regression was observed between CSA and dietary FPH level (p = .006, R² = .574) and between sarcomere length and dietary FPH level (p = .018, R² = .788). An appropriate level of FPH down‐regulated myostatin 2 gene expression and up‐regulated proliferating cell nuclear antigen gene expression, while the expression of myogenic regulatory factors was not affected by dietary treatments (p > .05). To conclude, an appropriate level of FPH may improve muscle growth by regulating the expression of muscle growth‐related genes, and muscle microstructure and ultrastructure.     

Effects of dietary nucleotides supplementation on rainbow trout (Oncorhynchus mykiss) performance and acute stress response

This experiment was conducted to examine the effect of dietary nucleotides (NT) on fish performance and acute stress response on fingerling rainbow trout (23 g ± 0.01, mean weight ± SEM). Five experimental diets according to different levels of supplemented nucleotides (0, 0.05, 0.1, 0.15, and 0.2%) were assayed on experimental fish for 8 weeks. Growth, hematological parameters (hematocrit, hemoglobin, erythrocyte, lymphocyte, and neutrophil count), serum proteins (globulin, albumin), and plasma enzymatic activity (alkaline phosphatase, ALP; aspartate transaminase, AST; lactate dehydrogenase, LDH; alanine transaminase, ALT) were assayed. At the end of feeding trial, fish fed the control and 0.2% diets were subjected to handling and crowding stress. Modulatory effects of nucleotides on acute stress response (cortisol and glucose) and plasma electrolytes (Na⁺, Cl⁻, K⁺, and Ca²⁺) were studied. The percentage of body weight gain (WG) and feed efficiency (FE) of fish were better when the fish were fed 0.15–0.2% diets. Fish fed the nucleotide-supplemented diets tended to have lower levels of serum enzymes including ALP, AST, LDH, and ALT. Plasma cortisol levels of fish fed on 0.2% diet under handling and crowding stress were significantly lower than fish fed the control diet at all post-stress time intervals. In our study, fish fed nucleotide-supplemented diet had significantly lower concentrations of glucose compared to those fed the basal diet. The concentrations of sodium, chloride, calcium, and potassium of fish fed the control diet were significantly lower than in fish fed nucleotide-supplemented diet. Dietary nucleotides administration seems to promote growth and to enhance resistance against handling and crowding stress in fingerling rainbow trout.