Effects of fish meal replaced by fermented soybean meal on growth performance,intestinal histology and microbiota of largemouth bass (Micropterus salmoides)

This study was conducted to investigate the effects of replacing fish meal (FM) with fermented soybean meal (FSM) and soybean meal (SM) on growth performance, intestinal histology and microbiota of largemouth bass (Micropterus salmoides). The basal diet contained 350 g/kg FM (CON), and then, FM was replaced with SM and FSM at the ratios of 30% and 60% (SM‐30, SM‐60, FSM‐30 and FSM‐60), respectively. The largemouth bass (4.43 ± 0.13 g) were fed for 8 weeks. The results showed that weight gain of fish fed with FSM‐60 and SM‐60 diets was significantly lower, and feed conversion ratio of SM‐30, SM‐60 and FSM‐60 groups was significantly higher than the CON group (p < .05). The intestinal villus height of SM‐60 group and the villus width of SM‐60 and FSM‐60 group were significantly lower than the CON group (p < .05). The 30% FM replacement by SM and FSM significantly increased the abundance of Cetobacterium and Mycoplasma, respectively (p < .05). In conclusion, FSM could replace 30% FM in diet without negative impacts on the growth performance of largemouth bass, while the SM should be controlled below 30%.     

An evaluation of replacing fish meal with fermented soybean meal in the diets of largemouth bass (Micropterus salmoides): Growth,nutrition utilization and intestinal histology

A 56‐day feeding trial was conducted to investigate the effects of replacing fish meal (FM) with soybean meal (SBM) and fermented soybean meal (FSBM) on growth performance, nutrition utilization and intestinal histology of largemouth bass. The basal diet contained 350 g/kg FM (control), and then, FM was replaced with SBM or FSBM of 15%, 30%, 45% and 60% respectively. The results showed that the specific growth rate of fish fed FSBM‐60, SBM‐45 and SBM‐60 diets significantly decreased, and the feed conversion ratio of SBM‐30, SBM‐45, SBM‐60, FSBM‐45 and FSBM‐60 groups increased when compared to the control group (p < .05). The apparent digestibility coefficients of dry matter and crude protein of SBM‐45, SBM‐60 and FSBM‐60 groups were significantly lower than those of the control group (p < .05), and the substitution of FM with SBM and FSBM (45% and 60%) significantly reduced the protein retention (p < .05). Serum total protein contents of SBM‐60 and FSBM‐60 groups and serum cholesterol contents of SBM‐45, SBM‐60 and FSBM‐60 groups were significantly lower than those of the control group (p < .05). The SBM‐30 and SBM‐60 groups showed significantly higher alanine aminotransferase activity than the control group (p < .05). The intestinal histology analysis resulted that the villus length of the SBM‐60 group and the villus width of the SBM‐45, SBM‐60 and FSBM‐60 groups decreased when compared to the control (p < .05). In conclusion, FSBM could replace 30% FM in diet of largemouth bass containing 350 g/kg FM, while the substitution level of FM with SBM was only 15%.     

High dietary starch impaired growth performance,liver histology and hepatic glucose metabolism of juvenile largemouth bass,Micropterus salmoides

A 60‐day experiment was carried out to investigate dietary starch levels on growth performance, hepatic glucose metabolism and liver histology of largemouth bass, Micropterus salmoides. Fish (initial weight 22.00 ± 0.02 g) were fed five graded levels of dietary corn starch (0, 50, 100, 150 and 200 g/kg). Fish fed low (0 and 50 g/kg) dietary starch showed significantly higher weight gain than other groups (p < .05). Liver lipid and glycogen accumulations were induced when dietary starch higher than 100 g/kg. After 20 days of feeding, hexokinase activity and mRNA expression were decreased in fish fed dietary starch higher than 150 g/kg (p < .05) and the pyruvate kinase showed the opposite tendency. Insulin receptor 1 (irs1), glucagon‐like peptide‐1 receptor and glucose transport protein 2 (glut2) mRNA expression were decreased with the increasing dietary starch after 10 days of feeding (p < .05). These results indicated gluconeogenesis was depressed and β‐oxidation was enhanced in response to high dietary starch, while the glycolysis was inhibited and endocrine system was impaired when fish fed high dietary starch; then, glucose homeostasis was disturbed and finally led to the glucose intolerance of largemouth bass.     

Effects of gelatin or carboxymethyl cellulose supplementation during pelleting processing on feed quality,intestinal ultrastructure and growth performance in gibel carp (Carassius gibelio)

Gelatin and carboxymethyl cellulose (CMC) were often used as binders due to their binding ability. To investigate the effects of gelatin and CMC supplementation on feed quality, intestinal ultrastructure and growth performance of gibel carp, six pelleted feed were formulated: control; supplemented with gelatin (10 g/kg, 30 g/kg and 50 g/kg); and supplemented with CMC (10 g/kg and 30 g/kg). Increased gelatin supplementation levels reduced feed solubility and pellet softening (p < .05) and decreased chemical oxygen demand in the surrounding water after pellets were immersed (p < .05). Increased levels of gelatin supplementation enhanced digesta viscosity and reduced intestinal microvilli length and digestive enzymes activities (chymotrypsin and amylase; p < .05) of fish. Fish‐fed diets supplemented with 30 g/kg gelatin had higher levels of plasma total free amino acids and glucose (p < .05) than fish fed 10 g/kg and 50 g/kg gelatin. Feed supplemented with 10 g/kg CMC were softer than those supplemented with 30 g/kg CMC (p < .05); fish‐fed diets supplemented with 10 g/kg CMC had longer intestinal microvilli (p < .05) than fish fed 30 g/kg CMC. Thus, our results indicated that either gelatin or CMC is applicable to supplement in the feed for improving feed quality and without negative effect on growth performance of gibel carp.     

Effect of dietary sodium butyrate on growth performance,enzyme activities and intestinal proliferation‐related gene expression of juvenile golden pompano Trachinotus ovatus

The present study was conducted to investigate the effects of dietary sodium butyrate on growth performance, intestine enzyme activities and intestinal proliferation‐related gene expression of juvenile golden pompano Trachinotus ovatus. A basal diet was supplemented with sodium butyrate at 0.0 (control), 0.25, 0.5, 1, 2 and 4 g/kg feed for 8 weeks. The final body weight, weight gain (WG), specific growth rate (SGR) and condition factor (CF) increased with increasing dietary sodium butyrate up to 2.0 g/kg, and thereafter declined, while feed conversion ratio exhibited an opposite trend. Compared with the control, the 2.0 g/kg sodium butyrate group had higher condition factor (CF) significantly (p < 0.05). Whole body ash decreased with increasing dietary sodium butyrate level, with the lowest whole body ash content in 4.0 g/kg sodium butyrate (p < 0.05). Compared with the control, the 2.0 g/kg sodium butyrate group had significantly increased plasma glucose, cholesterol, albumin level, A/G ratio, ALT and AST contents (p < 0.05), while significantly decreased plasma ALT/AST ratio (p < 0.05). As for the intestinal digestive and brush border enzymes activities, compared with the control, the 2.0 and 4.0 g/kg sodium butyrate groups had significantly increased intestinal protease, amylase, AKP and Na⁺‐K⁺‐ATPase activities (p < 0.05), respectively. The relative level of intestinal CDX2 mRNA of fish significantly increased with dietary sodium butyrate level. Compared with the control, the 2.0 g/kg sodium butyrate groups had significantly increased the expression of intestinal CDX2 and CREB mRNA (p < 0.05), respectively. In conclusion, these results suggested that the optimum sodium butyrate level for juvenile golden pompano could be 2.0 g/kg of the diet.     

Partial substitution of soybean meal with fermented soybean residue in diets for juvenile largemouth bass,Micropterus salmoides

A feeding trial was conducted to investigate the effects of partial replacement of soybean meal (SBM) with fermented soybean residue (FSR) on growth performance, body composition and plasma biochemical parameters of largemouth bass, Micropterus salmoides. Soybean residue was fermented with a mixture of microorganisms (Bacillus subtilis, Lactobacillus spp. and Molasses yeast) using the solid‐state fermentation. Four isonitrogenous (crude protein 430 g/kg) and isoenergetic (gross energy 18 MJ/kg) diets were formulated by replacing 0 (the control), 20, 40 and 60g/kg of protein from SBM with FSR (FSR0, FSR20, FSR40 and FSR60, respectively). Each diet was fed to four replicate groups of fish (initial body weight: 17.1 ± 0.19 g) for 12 weeks. Results showed that dietary FSR substitution significantly improved growth of juvenile largemouth bass. The weight gain, specific growth rate and protein efficiency ratio were all significantly improved by dietary FSR level up to 40g/kg substitution level (p < .05) and then levelled off beyond this level. Fish fed the diet with 40g/kg and 60g/kg protein from FSR had lower feed conversion ratio than the control group (p < .05). The hepatosomatic index, viscera ratio and liver lipid content significantly decreased with increasing dietary FSR level. Total protein content, superoxide dismutase and alkaline phosphates activities in plasma were lower in fish fed the control diet (p < .05) than the other groups. However, both alanine aminotransferase and aspartate transaminase were higher in fish fed the control diet (p < .05) compared to the other treatments. The plasma catalase activity significantly increased with increasing dietary FSR level, while plasma triglyceride, total cholesterol, glucose and malondialdehyde contents significantly reduced. No significant difference was observed in the glutathione peroxidase activity among dietary treatments. These findings demonstrated that replacing dietary SBM with FSR has beneficial effects on growth of M. salmoides, and the best growth performance was obtained at 40g/kg replacement for SBM protein. In addition, there is a great potential to apply FSR to improve lipid metabolism and antioxidant capacity of M. salmoides.     

High dietary starch inclusion impairs growth and antioxidant status,and alters liver organization and intestinal microbiota in largemouth bass Micropterus salmoides

Five diets (D1, D2, D3, D4 and D5) containing 0, 50, 100, 150 and 200 g starch per kg diet were formulated to investigate the effects of starch level on largemouth bass, Micropterus salmoides. Fish (initial weight: 22.00 ± 0.02 g) were fed the five diets for 90 days. Results indicated that weight gain, specific growth rate and survival of fish fed higher dietary starch level (200 g/kg) were lower than those of fish fed the lower dietary starch levels (0–50 g/kg). Higher dietary starch levels (150–200 g/kg) have a negative effect on antioxidant ability (total superoxide dismutase: T‐SOD; malonyldialdehyde: MDA; total antioxidant capacity: T‐AOC; glutathione peroxidase: GSH‐Px) and liver health (cellular contents leaked, nucleus deformed, endoplasmic reticulum and golgi body disappeared) of largemouth bass. Lower dietary starch levels (0–50 g/kg) modified intestinal microbiota of largemouth bass represented by increasing the relative abundance of beneficial bacterial such as Bacilli, Lactobacillales and Bacteroidales. These results indicated that dietary starch level above 50 g/kg had a negative effect on growth performance and antioxidant status of largemouth bass. Moreover, high dietary starch levels are potentially associated with negative alterations in liver structure and function, and decrease of beneficial gut microbes.     

The optimal dietary protein level of juvenile silver sillago Sillago sihama at three dietary lipid levels

A 5 × 3 factorial growth trial was conducted to evaluate optimal dietary protein and lipid levels (dietary protein level, DP; dietary lipid level, DL) for juvenile Sillago sihama (S. sihama) (2.0 ± 0.02 g, initial weight). Fish were fed 15 diets containing 5 DPs (350, 400, 450, 500 and 550 g/kg) and 3 DLs (60, 90 and 120 g/kg) for 8 weeks. The interaction between proteins and lipids significantly influenced the feed conversion ratio, condition factor, body composition, antioxidant indices and lipase activity (p < .05). DP 450 g/kg showed the highest average final body weight. DPs 500 and 550 g/kg significantly decreased the protein efficiency ratio (p < .05). DL 120 g/kg showed the highest percentage weight gain. The low feed conversion ratio was found in diets P45L12, P55L9 and P55L12. Diet P45L12 showed high superoxide dismutase activities. DP 450 g/kg showed the lowest average malondialdehyde content. Lipase activity was increased by increasing DP (p < .05) with a fall at DP 550 g/kg. Under the present experimental conditions, the optimal DP for S. sihama was 450 g/kg under the DL 120 g/kg.     

Zingiber officinale and Glycyrrhiza glabra,individually or in combination,reduce heavy metal accumulation and improve growth performance and immune status in Nile tilapia,Oreochromis niloticus

This study evaluated the impact of dietary ginger and liquorice supplementation on growth performance, physiological and histopathological profiles and heavy metal accumulation in Nile tilapia fingerlings. Fish (n = 1,800, 17.5 ± 0.11 g BW) were randomly distributed into four treatment groups in triplicates and received no supplementation (control group), 5 ml aqueous ginger extract/kg feed (ginger group), 4 ml aqueous liquorice extract/kg feed (liquorice group) or 2.5 ml ginger plus 2 ml liquorice aqueous extracts/kg feed (mix group). The ginger‐liquorice mix supply improved the growth performance and feed efficiency (p < .05), increased the haematocrit and haemoglobin (p < .05), leucocytes (p = .108), neutrophils (p = .054), serum total protein (p < .05), albumin (p = .011) and globulin (p = .094) but decreased (p < .05) the blood urea nitrogen and creatinine than feeding liquorice or ginger lonely compared to the control. Heavy metal loads in pond water induced lamellar telangiectasis of gills and necrosis with sloughing of intestinal villi tips. These detrimental effects were alleviated, and the intestinal villus length (p = .041) and crypt depth (p = .069) were increased with liquorice supply. In all treatment groups, heavy metal contents in fish flesh were lower compared to the control. Thus, using ginger and/or liquorice aqueous extracts can decrease heavy metal accumulation in the fish flesh and exert positive effects on growth performance, metabolic profile and the intestinal and gill morphology of Nile tilapia.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Effects of exogenous multienzyme complex supplementation in diets on growth performance,digestive enzyme activity and non‐specific immunity of the Japanese seabass,Lateolabrax japonicus

This experiment aimed to investigate the effects of exogenous multienzyme complex (EC) on growth performance, digestive enzyme activity and non‐specific immunity of the Japanese seabass, Lateolabrax japonicus (initial weight 27.09 ± 0.08 g). EC includes protease, xylanase, glucanase and mannase. Japanese seabass were given six levels of EC (0, 0.5, 1.0, 1.5, 2.0 and 2.5 g/kg) for 28 days. Results show that EC significantly enhanced the weight gain rate and specific growth rate (p < .05), while the feed conversion ratio reduced significantly (p < .05). Activities of lipase and trypsin in liver and intestine significantly increased (p < .05). Alkaline phosphatase, superoxide dismutase and lysozyme activities in serum and liver significantly increased (p < .05), while the content of malondialdehyde in liver significantly declined (p < .05). Regression analysis showed that the optimal supplementation of EC in WGR, SGR, FCR, SOD and LZM activity in serum was 1.66, 1.67, 1.81, 1.71 and 1.53 g/kg, respectively, while the best SOD, LZM activity in liver, trypsin activity in liver and intestine supplement were 1.64, 1.51, 1.81 and 1.97 g/kg. In conclusion, EC supplemented can improve the growth performance, digestive enzyme activity and non‐specific immunity of Japanese seabass, and it is recommended that the optimal supplementation of EC in diets of Japanese seabass is 1.5–2.0 g/kg.     

Effects of a highly purified fucoidan from Undaria pinnatifida on growth performance and intestine health status of gibel carp Carassius auratus gibelio

A six‐week feeding trial was conducted to determine the effects of different concentrations of fucoidan (1 g/kg, 10 g/kg and 30 g/kg; w/w) from Undaria pinnatifida on gibel carp (Carassius auratus gibelio). Our results demonstrated that 30 g/kg fucoidan significantly increased (p < .05) growth performance, intestinal digestive enzyme activities, acid phosphatase activity and immunoglobulin M content. Histological examinations revealed that gibel carp receiving 30 g/kg fucoidan had significant higher abundance of mucin‐containing goblet cells in middle and distal intestine as compared with control treatment (p < .05). Intestinal microbiota analysis showed that 30 g/kg fucoidan supplementation significantly increased (p < .05) the abundance of Cetobacterium and Aeromonas, but lowered (p < .05) the prevalence of pathogenic bacteria Plesiomonas and a mucin‐degrading bacterium Mucinivorans. Furthermore, RNA‐seq and RT‐qPCR analysis indicated that 30 g/kg fucoidan caused significant changes (p < .05) in the expression of genes involved in immune regulation (such as interleukin‐8 and cyclooxygenase), signal transduction (such as phosphatidylinositol‐4,5‐bisphosphate 3‐kinase and protein kinase B) and nutrition utilization (maltase–glucoamylase and muscarinic acetylcholine receptor 3). Together, the current study shows that fucoidan supplementation could elevate the activity of intestinal digestive enzymes, modulate intestinal microbial communities and potentiate a higher state of immune readiness, which might consequently improve growth performance and intestine health status of gibel carp.     

Effects of dietary inulin and Jerusalem artichoke (Helianthus tuberosus) on intestinal microbiota community and morphology of Nile tilapia (Oreochromis niloticus) fingerlings

This study investigated the effects of dietary inulin and Jerusalem artichoke (JA) on intestinal microbiota and morphometry of Nile tilapia fingerlings. Five treatment diets were designed to supplement inulin at 0 (basal diet), 2.5 and 5.0 g/kg, and JA at 5.0 and 10.0 g/kg. Nile tilapia larvae were fed experimental diets from the first feeding through the fingerling stage (84 days). The cultivation‐dependent technique showed that dietary inulin at 5.0 g/kg and JA (at both levels) increased lactic acid bacteria and Bifidobacterium spp., but decreased Vibrio spp. (p < .05). PCR‐DGGE targeting 16S ribosomal RNA gene revealed that dietary inulin and JA generated different profiles of microbial community compared with fish fed a basal diet. Compared with fish fed the basal diet, a greater intestinal villi height was observed in fish fed 5.0 g/kg inulin and JA at both levels (p < .05). A larger relative goblet cell number were observed in the anterior intestine of fish fed 5.0 g/kg inulin or JA (p < .05). Overall, dietary inulin (5.0 g/kg) and JA (5 and 10.0 g/kg) since the first feeding had effects on modulating the intestinal microbiota and morphology of Nile tilapia fingerlings.     

Dietary monosodium glutamate supplementation during the feed training of pacamã (Lophiosilurus alexandri): Growth performance and intestinal histomorphometry

Feed training of carnivorous fish is a delicate and stressful process. Thus, feed additives that reduce stress and encourage fish consumption could improve training efficiency. Therefore, the aim of this study was to evaluate monosodium glutamate (MSG) dietary supplementation during pacamã (Lophiosilurus alexandri) feed training through growth performance and intestinal histomorphometry. Fish were trained by the method of gradual diet transition, using five diets with increasing proportions of commercial diet and decreasing proportions of gelatin. A quadruplicate experimental design was performed with seven treatments, consisted in diets supplemented with different levels of MSG (0.0; 2.0; 8.0; 16.0; 29.0; 34.0 and 42.0 g/kg). Pacamã (0.17 ± 0.01 g) were distributed in 28 tanks (30 fish per tank) and trained for 41 days with the experimental diets. There were no effects (p > .05) of MSG on growth performance and feed training indices. However, fish trained with diets supplemented with 42.0 g/kg of MSG presented higher number of goblet cells in the anterior portion of intestine (p < .05). These results demonstrate that MSG did not act on growth performance and feed training efficiency of pacamã, and high levels of MSG can cause dietary stress on fish intestinal mucosa.     

Growth performance,immune response and disease resistance of rainbow trout (Oncorhynchus mykiss) fed Thymus vulgaris essential oils

Efficacy of Thymus vulgaris essential oils was assessed on growth, immune response and disease resistance of rainbow trout (Oncorhynchus mykiss). Fish weighing 10 g were fed with dietary supplemented of the oils at 0.5, 1.0 and 2.0 ml/kg feed for 2 months. Fish fed with the oils at 0.5 ml/kg feed demonstrated a better weight gain and specific growth rate, compared to other treatments (p < .05). Fish fed with 1.0 ml the oils showed the highest up‐regulation of complement component 3 (C3) and (cluster of differentiation 4) (CD4) genes expression (p < .05), while lysozyme gene expression level significantly increased in fish fed with 2.0 ml of the oils. In addition, at the end of the experiment, the expression of C3 and CD4 genes were significantly up‐regulated in fish fed with 1.0 and 2.0 ml of the oils, while IL‐1ß and lysozyme genes expression levels were significantly decreased in fish fed 2.0 ml oils, towards the end of the trial (p < .05). There was a fluctuation in the levels of Alanine aminotransferase, Aspartate aminotransferase and Alkaline phosphatase in all treatments during the experiment. When treated fish were challenged with Aeromonas hydrophila, the highest survival rate was observed in 0.5 ml/kg treatment, followed by 2 and 1 mg/kg treatments. Overall, these findings demonstrated that dietary administration of T. vulgaris oils especially at 0.5 mg/kg feed can be considered as a potential component for enhancing of the growth, immune responses and disease resistance of trout against motile Aeromonas septicemia caused by A. hydrophila.     

Effects of fishmeal replacement with cottonseed meal protein hydrolysate on growth,digestion and intestinal histology of juvenile Chinese soft‐shelled turtle,Pelodiscus sinensis

A 60‐day feeding experiment was conducted to evaluate the effects of fishmeal (FM) replacement with cottonseed meal protein hydrolysate (CPH) on growth, digestion and intestinal histology of juvenile Chinese soft‐shelled turtle (Pelodiscus sinensis). Five diets were formulated to replace 0, 50, 100, and 150 g/kg fishmeal protein by CPH (CPH0, CPH5, CPH10, CPH15) and CPH15L (CPH15 with micro capsule‐L‐lysine). Weight gain, feed conversion rate and protein efficiency ratio showed no significant differences compared to control group (p > .05). The highest feed intake indicated in CPH15 (p < .05). The composition of whole‐body varied slightly in each groups (p > .05). The trypsin activity significantly elevated when dietary fishmeal protein was replaced by CPH at 30–90 g/kg (p < .05). A significantly higher lipase activities in CPH5 than control group (p < .05). The CPH5‐10 groups showed higher villus height than the other groups (p < .05). The microvillus length in turtles with CPH showed a significant increasing length (p < .05). The results indicated that replacing up to 90 g/kg of dietary fishmeal protein with CPH did not hamper growth or reduce feed intake of turtles. Moreover, CPH replaced 60 g/kg FMP can increase intestine digestive enzymes activities and improve intestinal development.     

Growth,feeding and thyroxine‐related responses of hybrid striped (sunshine) bass (Morone chrysops ♀ X M. saxatilis ♂) fed de‐oiled carinata (Brassica carinata) meal

De‐oiled (<10 g/kg oil) carinata (Brassica carinata) meal is high (>400 g/kg) in protein, but its use in fish diets will likely be limited mainly by glucosinolates (GLS), sinapine and crude fibre. Two feeding experiments were conducted to determine the response of hybrid striped bass (Morone chrysops ♀ X M. saxatilis ♂, HSB) to inclusion of cold‐pressed carinata meal (CPCM) in diets. Cook extrusion reduced an average of 44% and 57% of GLS and sinapine concentrations in diets, respectively. In experiment 1, diets containing 0.71–2.71 μmoles of GLS and 0.034–0.181 mg of sinapine/g did not significantly (p > .05) reduce feed consumption, utilization or growth, resulting in similar concentrations of thyroxines and consequently no effect on deiodinase enzymes. In experiment 2, there was a significantly reduced (p < .05) feed consumption in fish fed diets containing 5.58–9.52 μmoles of GLS and 0.54–0.75 mg of sinapine/g, resulting in HSB exhibiting lethargic swimming and feeding behaviours, and consequently poor feed utilization and growth. Cook extrusion reduced about half of GLS and sinapine, and HSB tolerated ≤2.71 μmoles of GLS and ≤0.31 mg of sinapine/g of diet without affecting feed consumption and utilization, growth and thyroid metabolism.     

Growth performance,digestive and absorptive capacity of on‐growing grass carp (Ctenopharyngodon idellus) fed with graded level of dietary fibre from soybean hulls

The present research evaluated the effects of graded levels of dietary fibre on growth, digestive and absorptive capacities, and the potential underlying mechanisms in on‐growing grass carp (Ctenopharyngodon idella). Grass carp (123.00 ± 0.70 g) were fed diets with graded levels of neutral detergent fibre (NDF: 97.8, 119.0, 140.2, 159.4, 181.2 and 201.6 g/kg diet) for 60 days. Besides, a 2‐week digestion experiment was conducted to explore the effect of dietary fibre on the apparent digestibility coefficients (ADC) of feed. The results showed that optimum dietary fibre level (140.2 or 159.4 g/kg diet) increased feed intake, per cent weight gain, specific growth rate and the ADC of dietary protein (p < .05); increased the activities of digestive and brush border enzyme; and up‐regulated intestinal amino acid transporter mRNA levels (SLC1A5 and SLC6A19b, p < .05) partially associated with activation of TOR signalling pathway. However, high dietary fibre levels (NDF levels ≥181.2 g/kg diet) were not conducive to the digestion and absorption of nutrients, resulting in the decline of growth performance. Thus, based on the quadratic regression analysis for per cent weight gain and feed efficiency, the optimum (143.9 and 134.5 g/kg diet) and maximum tolerance (189.8 and 171.2 g/kg diet) levels of dietary NDF were estimated for on‐growing grass carp.     

Effects of fish origin probiotics on growth performance,immune response and intestinal health of shrimp (Litopenaeus vannamei) fed diets with fish meal partially replaced by soybean meal

This study was conducted to evaluate the application of four fish origin probiotics to relieve the side effects induced by SBM in shrimp. Shrimps were fed with high fish meal diet (C0, positive control containing 500 g/kg FM and 0 g/kg SBM), low fish meal diet (C, control containing 250 g/kg FM and 340 g/kg SBM) or the control diet (C) supplemented, respectively, with 1.0 × 10⁸ CFU/g Bacillus pumilus SE5 (T1), Psychrobacter sp. SE6 (T2), Enterococcus faecium MM4 (T3) or Bacillus claussi DE5 (T4). After 6 weeks of feeding, the growth performance, hepatopancreatic digestive enzymes, intestinal histological structure and immune parameters were determined. The results showed that compared with high FM group (C0), significantly lower WGR and SGR as well as higher FCR were observed in the low FM group (C) (p < .05). Compared with the control, significantly lower FCR was observed in treatment T1 (p < .05), but not in treatments T2–T4. Protease, amylase and lipase activities in all the treatments (T1‐T4) were significantly higher than the control (p < .05). GOT and GPT activities in the control were significantly lower than the C0 (p < .05), while higher MDA level was recorded in the control (p < .05). Meanwhile, higher GPT activities were observed in treatments T1‐T4 compared with the control (p < .05). Compared with the C0, lower SOD, ACP and AKP activities were observed in the control. Significantly improved SOD and AKP activities were observed in all probiotic feeding groups compared with the control (p < .05). The control diet led to significant reduction of intestinal wall thickness and villus height compared with the C0 (p < .05), while significantly higher intestinal wall thickness and villus height were exhibited in all the probiotic groups compared with the control (p < .05), except intestinal wall thickness in treatment T3. Thus, these results demonstrated that the four fish origin probiotic strains could relieve the side effects induced by high level of SBM in shrimp, while probiotic B. pumilus SE5 showed the best performance.     

Dietary calcium requirement of red swamp crayfish (Procambarus clarkia)

To investigate dietary calcium requirement of red swamp crayfish (Procambarus clarkia), six semi‐purified diets were formulated to contain different concentrations of calcium (2.7(control group), 6.1, 11.9, 17.6, 23.5 and 29.1 g/kg calcium). Each diet was hand‐fed to triplicate of 15 crayfish with average initial body weight (6.22 ± 0.87) g for 8 weeks. The results showed that weight gain rate (WGR) significantly increased and feed conversion ratio (FCR) significantly decreased from 11.9 to 23.5 g/kg groups (p < .05). Protease activities in intestine and hepatopancreas and parathyroid hormone concentrations in serum significantly decreased with increasing dietary calcium levels (p < .05), while calcium and phosphorus contents in exoskeleton, calcium content in muscle and calcitonin concentrations in serum significantly increased (p < .05). The activities of lipase and amylase in intestine and hepatopancreas, serum alkaline phosphatase and total vitamin D concentrations in serum had significant increase as dietary calcium content increased up to 11.9–17.6 g/kg (p < .05). The inorganic phosphorus content in 29.1 g/kg group was significantly lower than those in other groups (p < .05). Broken‐line model analysis based on WGR and quadratic curve model analysis based on FCR showed that optimal dietary calcium requirement of red swamp crayfish ranged from 12.7 to 17.1 g/kg.