High dietary energy level stimulates growth hormone receptor and feed utilization in large Atlantic salmon (Salmo salar L.) under hypoxic conditions

This study examines how appetite and growth regulation of Atlantic salmon are affected by low dissolved oxygen (LO) and dietary digestible energy levels (DE: high [HE] vs. low [LE]). Long‐term exposure to LO resulted in a reduced feed intake, growth, digestible protein and fat retention efficiencies and increased feed conversation ratio and plasma ghrelin concentrations (p < .05) compared to high dissolved oxygen (HO). Pair‐feeding of rations based on the feed intake of the LO groups, but fed at HO, resulted in a 50% growth improvement in HE diet groups. This suggests that the poor growth under LO was not entirely caused by the reduced feed intake. Salmon adapted to LO by increased haemoglobin concentrations, while osmoregulation was affected by increased plasma chloride concentrations (p < .05). Plasma ghrelin concentration was unaffected by DE (p > .05). Growth regulation was affected by the HE diet, with increased liver and muscle growth hormone receptor ghr1 mRNA (p < .05), regardless of oxygen level. The growth depression due to low oxygen appears to be related to higher metabolic costs, while higher DE upregulates the GH‐IGF system at the ghr1 level and found to be beneficial for growth, feed intake, oxyregulation and osmoregulation under hypoxia.     

The effect of dietary methionine concentrations on growth performance of juvenile Nile tilapia (Oreochromis niloticus) fed diets with two different digestible energy levels

A growth trial was conducted to examine the effect of dietary digestible energy (DE) content on methionine (Met) utilization and requirement in juvenile Nile tilapia (Oreochromis niloticus). Ten iso‐nitrogenous (288 g kg^?1 protein) practical diets, with two DE levels (10.9 MJ kg^?1; 12.4 MJ kg^?1) and five methionine supplementation levels (0, 1, 2, 4 and 6 g kg^?1), were hand‐fed twice daily to triplicate groups of Nile tilapia (initial body weight 8.95 ± 0.06 g) for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased significantly with increasing dietary methionine concentration at the same DE content (P < 0.001). At the same dietary methionine level, WG and SGR of fish fed high‐DE diets were significantly higher than that of fish fed low‐DE diets (P = 0.0001), although no interaction was found between dietary DE and methionine supplementation. Based on quadratic regression analysis between dietary methionine concentration and weight gain, optimal methionine requirement for maximum growth, expressed as g Met required kg^?1 diet (low‐ versus high‐DE diets), increased as diet DE concentration increased (7.34 versus 9.90 g kg^?1 diet, respectively; with cysteine 4.70 g kg^?1 diet). The results indicated that diet DE content affects methionine utilization and requirement in juvenile Nile tilapia, fish fed high‐DE diets required more methionine for maximum growth.     

Effects of dietary live or heat‐inactivated autochthonous Bacillus pumilus SE5 on growth performance,immune responses and immune gene expression in grouper Epinephelus coioides

To evaluate the possible dietary application of live and heat‐inactivated probiotic Bacillus pumilus SE5 in grouper Epinephelus coioides, juveniles (14.6 ± 0.2 g) were fed either a basal control diet (without probiotic) or the basal diet supplemented with 1.0 × 10⁸ CFU g^?1 live (T1) and heat‐inactivated B. pumilus SE5 (T2). The heat‐inactivated probiotic significantly improved the final weight, weight gain (WG) and specific growth rate (SGR) at day 60 and significantly decreased the feed conversion ratio (FCR) at day 30 and 60, while the viable probiotic significantly decreased the FCR at day 60 (P < 0.05). Phagocytic activity, serum complement C3 and IgM levels as well as SOD activity elevated significantly in fish fed the heat‐inactivated probiotic for 60 days (P < 0.05). Furthermore, the heat‐inactivated probiotic remarkably up‐regulated expression of TLR2 and pro‐inflammatory cytokines (IL‐8 and IL‐1β) in head kidney (P < 0.05), but the viable probiotic failed to do so. These results indicated that heat‐inactivated B. pumilus SE5 can effectively improve the growth performance and immune responses of E. coioides.     

Effects of four feeding stimulants in high plant‐based diets on feed intake,growth performance,serum biochemical parameters,digestive enzyme activities and appetite‐related genes expression of juvenile GIFT tilapia (Oreochromis sp.)

The present research evaluated the effects of four feeding stimulants on feed intake (FI), growth performance, body composition, serum biochemical parameters, digestive enzyme activities and appetite‐related gene expression for juvenile GIFT tilapia. Five experimental high plant‐based diets (with 0, 0.4 g kg^?1 dimethyl‐β‐propiothetin (DMPT), 0.6 g kg^?1 dimethylthetin (DMT), 1.8 g kg^?1 tryptophan (Trp) and 6 g kg^?1 betaine (Bet), respectively supplemented) were fed to juvenile GIFT tilapia (Oreochromis sp.) (3.34 ± 0.01 g) for 8 weeks. The results showed that FI was significantly increased by Trp and DMT. The highest specific growth rate (SGR) and protein efficiency ratio (PER) was observed for fish fed Bet diet, followed by DMT. Serum triglyceride was significantly increased by DMPT. Fish fed Bet diet showed significantly higher intestinal protease, liver protease and intestinal amylase activities. The neuropeptide Y (NPY) mRNA expression in brain was significantly improved by Trp, and ghrelin mRNA expression in stomach was significantly increased by DMT. It is concluded that supplementation of Trp or DMT could act as an effective feeding stimulants (FS) in high plant‐based diets for juvenile GIFT tilapia, which might be associated with the relatively higher orexigenic (NPY or ghrelin) genes expression, and supplementation of Bet could improve SGR, PER and reduce feed conversion ratio (FCR) of juvenile GIFT tilapia.     

Effects of dietary choline supplementation on growth performance,lipid deposition and intestinal enzyme activities of blunt snout bream Megalobrama amblycephal fed high‐lipid diet

This study aimed to investigate the effects of dietary choline supplementation on growth, lipid deposition and intestinal enzyme activities of Megalobrama amblycephala. Fish were fed four diets with two lipid levels (50 and 150 g kg^?1) and two choline supplementations (600 and 1600 mg kg^?1) for 8 weeks. Feed conversion ratio (FCR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, whole‐body and muscle lipid contents, intestinal lipase activities and lipoprotein lipase (LPL) activities all increased significantly (P < 0.05) as lipid levels increased, whereas the opposite was true for whole‐body and muscle moisture contents and intestinal amylase activities. VSI, IPF ratio and whole‐body lipid contents all decreased significantly (P < 0.05) with increasing dietary choline supplementations. Weight gain, muscle moisture content all increased significantly (P < 0.05) with increasing dietary choline supplementations when dietary lipid levels reached 150 g kg^?1, whereas the opposite was true for FCR, IPF ratio, IPF and liver LPL activities. In addition, abnormal hepatocytes were found in the liver of fish fed 150 g kg^?1 lipid with 600 mg kg^?1 choline supplementation. The result of this study indicated that extra choline supplementation can improve growth performance, intestinal enzymes activities and reduce excessive lipid deposition of M. amblycephala fed high lipid.     

Effect of dietary protein levels on growth and nutrient utilization of fringe‐lipped carp,Labeo fimbriatus (Bloch) fingerlings

Effect of various dietary protein levels on growth and nutrient utilization were studied in fringe‐lipped carp, Labeo fimbriatus fingerlings for 60 days. Five practical diets containing graded protein levels of 200, 250, 300, 350 and 400 g kg^?1 with respective digestible protein (DP) contents of 192.4, 244.5, 291.6, 339.4 and 391.4 g kg^?1 were evaluated as five treatments, T1, T2, T3, T4 and T5, respectively, in triplicate. Each experimental tank (80‐L) contained eight fingerlings (4.9 ± 0.1 g) and was subjected to continuous aeration and 25% water replenishment daily. The fish were fed two times daily at 8:00 and 14:00 h to satiation. Significantly higher (P < 0.05) absolute growth and thermal growth coefficient, and lower feed conversion ratios (FCR) were observed in T2–T4 than T1 and T5. Protein efficiency ratio (PER) and protein productive values (PPV) were highest in T2 and lowest in T5. Significantly higher (P < 0.05) apparent protein digestibility was perceptible in T2–T4. While specific amylase activity declined linearly with increasing DP : DE, the protease, trypsin, aspartate aminotransferase and alanine aminotransferase established polynomial relationship. Based on live weight gain, PER and PPV fitted to quadratic model optimum DP levels were estimated as 301.4, 260.0 and 273.0 g kg^?1, respectively.     

Effects of stocking density on growth performance and welfare‐related physiological parameters of Atlantic salmon Salmo salar L. in recirculating aquaculture system

Stocking density, representing a potential source of long‐term stress, is widely recognized as a critical factor in aquaculture husbandry. Atlantic salmon were reared at low‐density (LSD, ~9.80–18.41 kg m^?3, initial to final density), medium‐density (MSD, ~19.62–36.96 kg m^?3) and high‐density (HSD, ~28.79–53.54 kg m^?3) stocking levels for 66 days to investigate the stress‐induced changes in fish growth and welfare. At the end of the trial, the salmon in HSD group showed significant lower final weight and higher ration level than those in MSD and LSD groups (P < 0.05). The salmon farmed in LSD group had higher special growth rate (SGR) and lower feed conversion ratio (FCR) (P < 0.05). However, stocking density could not affect the mortality, condition factor and coefficient of variation of salmon. The pectoral fin index of salmon in LSD group was significantly higher than that in HSD group (P < 0.05). Fifteen haematological and serum parameters were detected to assess the stress and welfare levels of salmon. The salmon farmed in HSD group had higher glucose (GLU) level and lower Cl^?, haemoglobin (HGB) and red blood cell (RBC) concentrations (P < 0.05). Contrast to the pattern of superoxide dismutase (SOD) activity, the cortisol, maleic dialdehyde (MDA) and alkaline phosphatase (ALP) levels of HSD group were higher than those in other two groups (P < 0.05). All these findings will provide a reference for selecting suitable stocking density in Atlantic salmon farming industry.     

Effects of dietary choline on growth performance,lipid deposition and hepatic lipid transport of grouper (Epinephelus coioides)

The number of 360 individuals with an average initial weight of 87.8 ± 0.04 g was fed six diets containing graded levels of choline at 8.1 (control group), 602.5, 1119.0, 1511.5, 1970.0 and 4029.0 mg choline kg^?1 diet, respectively, to investigate the effects of dietary choline on growth performance, lipid deposition and hepatic lipid transport for grouper, Epinephelus coioides. Dietary methionine was estimated to be 10.02 g kg^?1, less than the requirement (13.10 g kg^?1). The results of 10‐week study period indicated that the best values of specific growth rate (SGR), feed conversion rate (FCR) and protein efficiency rate (PER) all occurred in 1119.0 mg choline kg^?1 diet (P < 0.05). The survival range increased from 8.1 to 1511.5 mg choline kg^?1 diet and then plateaued. Dietary choline supplementation significantly decreased the liver lipid content of grouper (P < 0.05), but the lipid content of the muscle tended to be increased firstly and then decreased (P < 0.05). Liver choline concentration reached a plateau in 1511.5 mg choline kg^?1 diet and then levelled off (P < 0.05). Serum high density lipoprotein‐cholesterol (HDL‐C) and total cholesterol (TCHO) levels were firstly decreased and then increased with dietary choline supplementation. A reversed tendency, however, was found in triglyceride. Broken‐line regression analysis of SGR and liver choline content indicated that choline requirement of grouper was 1093.7 and 1579.7 mg kg^?1 diet, respectively.     

Dietary methionine requirement of juvenile Pseudobagrus ussuriensis

An 8‐week feeding trial was conducted to determine the optimum dietary methionine (Met) requirement of juvenile Pseudobagrus ussuriensis with an initial average weight of 0.60 g reared in indoor flow‐through and aerated aquaria. Six isonitrogenous (430 g kg^?1 protein) and isolipidic (50 g kg^?1 lipid) test diets were formulated to contain graded levels of crystalline L‐methionine (4.9, 9.0, 11.8, 14.2, 18.1 and 20.8 g kg^?1 dry diets, respectively) at a constant dietary cystine level of 2.5 g kg^?1 dry diets. Equal amino acid nitrogen was maintained by replacing methionine with non‐essential amino acid mixture. Fish were randomly allotted to 18 aquaria (1.0 × 0.5 × 0.8 m) with 50 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. No significant difference was observed in survival of fish (84.67–91.33%). Specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR), protein productive value (PPV) and protein efficiency ratio (PER) were significantly affected by different dietary methionine levels (P < 0.05). WG, SGR PPV and PER increased, while FCR decreased with increasing dietary methionine level from 4.9 to 11.8 g kg^?1 (P < 0.05). However, with further increase from 11.8 to 20.8 g kg^?1, WG, SGR PPV and PER significantly decreased, FCR increased (P < 0.05). The whole body and muscle composition were affected by different dietary methionine levels (P < 0.05). Condition factor (CF) increased with increasing dietary methionine levels up to 11.8 g kg^?1 (P < 0.05) and after 11.8 g kg^?1 methionine diet, but not significant, declines were observed (P > 0.05). Hepatosomatic index (HSI) of the 4.9, 9.0, 11.8 and 14.2 g kg^?1 Met diets was significantly higher than that of fish fed diets 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Viscerosomatic index (VSI) of the 4.9, 9.0 and 11.8 g kg^?1 Met diets was significantly higher than that of fish fed diets 14.2, 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Quadratic regression analysis of WG and PER against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth and feed utilization of juvenile Pseudobagrus ussuriensis was 14.3 and 14.1 g kg^?1 dry diet (35.3 and 34.8 g kg^?1 dietary protein), respectively, in the presence of 2.5 g kg^?1 dry diets cystine.     

Growth performance and TOR pathway gene expression of juvenile blunt snout bream,Megalobrama amblycephala,fed with diets replacing fish meal with cottonseed meal

A 16‐week feeding trial was conducted to assess the effects of replacing fish meal (FM) with cottonseed meal (CM) on the growth performance, feed utilization, plasma biochemical composition and target of rapamycin (TOR) pathway gene expression of juvenile blunt snout bream (Megalobrama amblycephala). Five isonitrogenous (36% crude protein) and isoenergetic (16 MJ kg^?1) diets with graded replacing levels of CM (replacing 0, 25, 50, 75 and 100% FM with CM) and similar lysine and methionine concentrations were fed to triplicate groups of fish. Results revealed that specific growth rate (SGR), feed intake and protein efficiency ratio (PER) of group fed with diets replacing FM with CM up to 50% were significantly higher than others (P < 0.05). However, final body weight and feed conversion ratio (FCR) remained similar up to 25% and thereafter significantly decreased and increased, respectively, as the replacement level increased (P < 0.05). Replacement levels significantly decreased hepatosomatic index and viscerosomatic index (P < 0.05), but did not significantly affect condition factor and whole body compositions. Free gossypol mainly accumulated in liver and significantly increased in diets CM75 and CM100 than CM0 (P < 0.05). Replacement significantly influenced plasma urea contents (P < 0.05). Meanwhile, increasing replacement of FM with CM in diets increased insulin‐like growth factor I (IGF‐1) gene expression in liver of blunt snout bream. Target of rapamycin (TOR) gene expression in diet CM100 was significantly lower than that in diets CM0 and CM75, while the eukaryotic translation initiation factor 4E‐binding protein 2 (4E‐BP2) gene expression was not affected by the replacement level of CM in diets. Therefore, based on final body weight and FCR, it suggested that up to 25% of FM (150 g kg^?1 in basal diet) could be replaced by CM in diets, which was 112.5 g kg^?1 FM and 192.9 g kg^?1 CM, for juvenile blunt snout bream.     

Effects of dietary chitosan oligosaccharide complex with rare earth on growth performance and innate immune response of turbot,Scophthalmus maximus L.

An 8‐week‐feeding trial was conducted to investigate the effect of dietary chitosan oligosaccharide complex with rare earth (COS‐REE) on growth performance and innate immune response of turbot, Scophthalmus maximus L. (Initial average weight was (12.1 ± 0.1) g) as well as disease resistance against Edwardsiella tarda. Six practical diets (approximately 53.01% protein and 12.57% lipid) were formulated to contain graded levels (0, 75, 150, 300, 600 and 1200 mg kg^?1) of COS‐REE. Results of the present study showed that, compared to the control group (0 mg kg^?1), the specific growth rate (SGR) was significantly higher in fish fed the diet with 300 mg kg^?1 COS‐REE (P < 0.05), while the feed conversion ratio (FCR) significantly decreased (P < 0.05). The phagocytic index (PI) and the activity of super oxide dismutase (SOD) of serum in fish fed the diet with 300 mg kg^?1 COS‐REE was significantly higher than fish fed the control diet (P < 0.05), but no significant differences were observed in malondialdehyde (MDA) and hepatic metallothionein (MT) concentrations. After 8 weeks, fish were challenged by intraperitoneal injection with E. tarda, and COS‐REE‐treated fish demonstrated increased protection capability. These results suggested that COS‐REE could enhance growth, innate immunity and disease resistance in turbot, and the optimum dose was approximately 300 mg kg^?1.     

Replacement of fish oil with alternative lipid sources in plant‐based practical feed formulations for marine shrimp (Litopenaeus vannamei) reared in outdoor ponds and tanks

The objective of this study was to demonstrate the feasibility of partial substitution of menhaden fish oil by alternative lipid sources (soybean oil, poultry grease and flaxseed oil) in non‐marine protein‐based shrimp production diet, its influence on fatty acid profile and its final product flavour. Results for the pond study (17 weeks) showed no differences (P ≥ 0.05) in shrimp production among different test diets. Production ranged from 5070 to 5363 kg ha^?1; mean final weight, 18.0 to 21.6 g; weekly growth, 1.04 to 1.25 g; survival, 65.6 to 75.4%; and FCR, 1.37 to 1.45. Results from the tank trial (12 weeks) confirmed these findings, final weight, 13.8–14.8 g; weekly growth, 1.1–1.2 g; survival, 92.5–98.3%; FCR, 1.05–1.11; and final standing crop, 4738–5024 kg ha^?1. The fatty acids profiles of edible tail muscle reared on the various diets displayed a similar fatty acid profile to that of the diets. The sensory test showed no statistical differences in texture, appearance, aroma and flavour between the shrimp fed diets containing menhaden fish oil and soybean oil. These studies demonstrated that practical shrimp feeds containing non‐marine protein ingredients and a percentage of fish oil replaced by alternative lipid sources had no negative impact on mean final weight, weekly growth, survival, FCR, final standing crop, fatty acids profile and organoleptic properties of Litopenaeus vannamei.     

Effect of dietary supplementation of probiotic on performance and intestinal microflora of Chinese soft‐shelled turtle (Trionyx sinensis)

This experiment was conducted to study the effect of dietary supplementation of probiotic on performance and intestinal microflora of Chinese soft‐shelled turtle. Healthy Chinese soft‐shelled turtles (6000 pieces with average weight of 5 g) were selected and randomly divided into two groups: control and treatment with three replicates each. The control was fed on normal basal diet, whereas treatment was fed on basal diet supplemented with 1 × 10⁸ cfu.g^?1 Bacillus subtilis preparation. The results showed that the final mean weight of treatment (265.84 ± 3.48 g) was significantly higher (P < 0.05) than that of control (240.45 ± 4.32 g). There was significant difference (P < 0.05) in FCR, and DGs were obtained in probiotics fed group as compared to control. The level of sucrase, maltase, amylase, lipase and ATPase of treatment was significantly higher (P < 0.05) than that of control. Pyrosequencing showed that the dietary supplementation of probiotic Bacillus strain decreased microbial diversity. Phylum Firmicutes was dominant in both groups. Compared with the control, Firmicutes was increased, while others were decreased in treatment group. The results indicated that dietary supplementation of probiotic can improve growth performance, digestibility and intestinal microflora in Chinese soft‐shelled turtle.     

Influence of dietary phosphorus levels on growth,body composition,metabolic response and antioxidant capacity of juvenile snakehead (Channa argus × Channa maculata)

A study was conducted to estimate the optimum requirement of dietary phosphorus (P) for Channa argus × Channa maculata. Effects of dietary P levels on the tissue composition, serum biochemical parameters and antioxidant status were also examined. Five practical diets were formulated to contain graded levels (4.8 g kg^?1, 6.4 g kg^?1, 7.9 g kg^?1, 9.4 g kg^?1 and 11.0 g kg^?1) of available P from dietary ingredients and monocalcium phosphate (MCP). Each diet was randomly assigned to triplicate groups of 30 juvenile fish (initial body weight, 20.50 ± 0.53 g) for 8 weeks. The results showed that the specific growth rate (SGR) and weight gain (WG) were all significantly improved by dietary P up to 9.4 g kg^?1 (P < 0.05) and then levelled off beyond this level. Broken‐line analysis showed maximum weight gain (WG) was obtained at dietary available P concentrations of 9.6 g kg^?1. With the increase in dietary P level, protein efficiency rate (PER) increased significantly and reached a plateau, while the feed conversion ratio (FCR), the mesenteric lipid somatic index (MSI) and the whole‐body lipid content significantly reduced (P < 0.05). Dietary P levels also affected the mineralization (ash and P) of whole body, vertebrae and scale (P < 0.05). Quadratic analysis based on P contents in whole body, vertebrae, scale and ash content in vertebra indicated that the available P requirements were 10.4, 9.8, 10.0 and 10.3 g kg^?1, respectively. However, no differences were found in the whole‐body moisture, crude protein, serum calcium (Ca) contents or Ca/P value, as well as the viscerosomatic index (VSI) and hepatosomatic index (HSI) among all the treatments (P > 0.05). Triglyceride (TG), total cholesterol (TC), high‐density lipoprotein cholesterol (HDL‐C) and low‐density lipoprotein cholesterol (LDL‐C) decreased significantly, while serum P content, HDL‐C/TC and HDL‐C/LDL‐C value increased significantly with dietary available P levels (P < 0.05). No significant changes in superoxide dismutase activity and malondialdehyde (MDA) content were observed (P > 0.05), but serum catalase (CAT) and glutathione peroxidase (GPx) activities and the ratio of CAT/SOD and GPx/SOD increased significantly with increasing dietary P levels (P < 0.05). In conclusion, the optimal P requirement of juvenile snakehead in practical feed was 9.6 g kg^?1. Signs of P deficiency were characterized by poor growth, slightly reduced mineralization and the antioxidant capacity and an increase in body lipid content.     

Effect of florfenicol and oxytetracycline treatments on the intensive larval culture of the Chilean scallop Argopecten purpuratus (Lamarck, 1819)

The administration of antimicrobials to control bacterial pathologies in Chilean scallop hatcheries is a frequent practice, but their effects on these cultures remained unknown. This study was undertaken to obtain information on the effect of the administration of florfenicol and oxytetracycline on the growth, survival and bacterial content of scallop larvae under farming conditions. Florfenicol‐treated cultures exhibited high survival rates (44% after 17 days of culture), whereas cultures not treated or treated with oxytetracycline collapsed after 11 days of culture. Surprisingly, no significant differences in the heterotrophic (Tukey test; P = 0.226) and Vibrio (Tukey test; P = 0.666) concentrations between the oxytetracycline‐treated and untreated larval cultures were observed. Otherwise, florfenicol administered directly into rearing tanks produced significantly higher larval growth (Tukey test; P = 0.0001) and survival (Tukey test; P = 0.011) than bath treatment. When 2 and 4 mg L^?1 of florfenicol were compared, no significant differences in growth (t‐test; P = 0.4596) and survival (Tukey test; P = 0.057) were observed, suggesting that a concentration of 2 mg L^?1 is sufficient to ensure larval production. The present results demonstrate the efficacy of florfenicol‐based therapy to increase larval survival and growth at commercial scale and prompt the necessity to standardize its use in Chilean scallop hatcheries.     

Effect of replacing fish meal with soybean meal and of DL‐methionine or lysine supplementation in pelleted diets on growth and nutrient utilization of juvenile golden pompano (Trachinotus ovatus)

The experiment was conducted to determine the effect of dietary DL‐methionine addition in fish meal reduction diet for juvenile golden pompano (Trachinotus ovatus). The trial comprises the following of 11 diet treatments. (i) D1 diet as the standard was formulated with fish meal as the main protein source. (ii) D2–D5 diets were formulated to replace fish meal with soybean meal at 60, 120, 180 and 300 g kg^?1, respectively, and the amino acid profiles (including methionine and lysine) of D2–D5 were referred to the amino acid profile of D1. (iii) D6‐D9 diets were the same as D2–D5, respectively, but without methionine supplementation. (iv) D10 and D11 diets were the same as D3 and D5 diets, respectively, but without lysine supplementation. Each diet was randomly fed to groups of 20 fish (initial average weight about 18 g) per net cage (1.0 × 1.0 × 1.5 m) in triplicate and the feeding experiment lasted for 56 days. Weight gain (WG, %) and final body weight (FBW, g) of fish fed D3 diet were significantly higher than those of fish fed D8 and D9 diets (P < 0.05), but without significant differences with fish fed other diets (P > 0.05). Feed conversion ratio (FCR) of D3, D4 and D5 diet treatments were significantly lower than that of D11 diet treatment (P < 0.05), but without significant difference with other diet treatments (P > 0.05). Whole‐body protein contents of fish fed D3–D5 were significantly higher than those of fish fed D7–D9 (P < 0.05), but without significant differences with fish fed other diets (P > 0.05). In conclusion, the replacement of fish meal by soybean meal could reach 300 g kg^?1 without detrimental but profitable effect on growth and survival when enough methionine and lysine were supplemented in the diet; moreover, lysine is not the first‐limiting amino acid relative to methionine for juvenile T. ovatus from the present growth and proximate composition results.     

Effects of temperature and feed processing on protease activity and dietary protease on growths of white shrimp,Litopenaeus vannamei,and tilapia,Oreochromis niloticus × O. aureus

Effects of temperature and processing on the stability of a commercial protease were assessed in an in vitro trial followed by growth trials with white shrimp and tilapia. Results showed that the protease has a high heat stability against pelleting, and it could hydrolyse dietary proteins during feed processing. In Exp. 2, white shrimp (3.3 g) fed low fish meal (FM) diet (LFD) with protease addition had similar growth to that fed high fish meal diet, and both had higher weight gain (WG) and lower feed conversion ratio (FCR) than that fed LFD without protease addition (P < 0.05). In Exp. 3, compressed (CD) or extruded (ED) diets containing 30 g kg^?1 or 90 g kg^?1 FM were supplemented with or without protease and then fed to tilapia (1.7 g) for 8 weeks. WG was improved and FCR decreased (P < 0.05) by the supplementation of protease in 30 g kg^?1 FMCD, but not in 90 g kg^?1 FMCD and ED diets when compared to those diets without protease supplementation. The digestibility trial with CD indicated the improved apparent digestibilities of dry matter and crude protein by dietary protease in 30 g kg^?1 FMCD, but not in 90 g kg^?1 FMCD. Results above showed that the protease has a high heat stability and the supplementation of protease in CD with low FM level can improve the growth of shrimp and tilapia.     

Effect of the addition of Chaetoceros calcitrans,Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and growth of Litopenaeus vannamei (Boone) postlarvae reared in a biofloc system

The aim of this study was to evaluate the effect of the addition of Chaetoceros calcitrans, Navicula sp. and Phaeodactylum tricornutum (diatoms) on phytoplankton composition and the growth of Litopenaeus vannamei postlarvae reared in a biofloc system . Four treatments were used: BFT (biofloc system without feed and no addition of diatoms); BFT‐F (biofloc system with feed and no addition of diatoms); BFT‐D (biofloc system with the addition of diatoms and no feed); and BFT‐FD (biofloc system with the addition of feed and diatoms), all in triplicate. The shrimp (16 ± 0.02 mg) were stocked at 2500 postlarvae m^?3 and fed a commercial feed. Diatoms were added on the 1st, 5th, 10th and 15th day at a density of 5 × 10⁴ cells mL^?1 for each species. No significant differences (P > 0.05) between treatments were observed for gross primary production, net ecosystem production and water column respiration rate. However, significant differences (P < 0.05) were observed for nitrite, orthophosphate, alkalinity, final weight, weight gain, yield, feed conversion ratio (FCR), phytoplankton and cyanobacteria composition. The BFT‐FD treatment had better performance parameters for final weight (270 mg), weight gain (254 mg), yield (0.67 Kg m^?3) and FCR (0.61), indicating the benefits of the diatoms C. calcitrans, Navicula sp. and P. tricornutum for decreasing cyanobacteria and improving growth of L. vannamei postlarvae reared in biofloc systems.