Optimum dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus

A feeding trial of three protein (200, 300 and 400 g kg⁻¹) and two lipid levels (20 and 100 g kg⁻¹) was conducted to determine the proper dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus. Dietary protein and lipid levels were adjusted by adding with different levels of soybean meal, squid liver oil and soybean oil, respectively. Three replicate groups of sea cucumbers (average weight of 1.3 g) were fed the experimental diets for 12 weeks. At the end of the feeding trial, survival was not affected by dietary protein and lipid levels (P > 0.05). Weight gain (WG) and specific growth rate (SGR) of sea cucumbers were significantly affected by dietary protein (P < 0.006) and lipid levels (P < 0.001). The highest WG and SGR were observed in sea cucumbers fed the 200 and 400 g kg⁻¹ protein diet with 20 g kg⁻¹ lipid (P < 0.05). WG and SGR of sea cucumbers fed the diet containing 20 g kg⁻¹ lipid were higher than those of sea cucumbers fed the 100 g kg⁻¹ lipid diets (P < 0.05) at each dietary protein level. Apparent digestibility coefficients of dry matter, crude protein, carbohydrate and gross energy of sea cucumbers fed the 20 g kg⁻¹ lipid diets were significantly higher than those of the 100 g kg⁻¹ lipid diets at 200 and 400 g kg⁻¹ protein (P < 0.05). Moisture, crude protein, crude lipid and ash contents were not significantly different among the groups. The results of this study indicate that the diet containing 200 g kg⁻¹ protein (170 g kg⁻¹ digestible protein) with 20 g kg⁻¹ lipid (13 g kg⁻¹ digestible lipid) may be sufficient for optimum growth of juvenile sea cucumber.     

Distillers dried grain can be used as a feed ingredient for the growth of freshwater snail (Semisulcospira coreana) and abalone (Haliotis discus hannai)

Two feeding experiments were conducted to evaluate dietary distillers dried grain (DDG) as a feed ingredient that partially replaces soybean meal and wheat flour for the growth of juvenile freshwater snail (Semisulcospira coreana) and abalone (Haliotis discus hannai). Three experimental diets were formulated to contain 0 g kg^?1 DDG (DDG0), 200 g kg^?1 DDG from rice (diet DDG‐R) and 200 g kg^?1 DDG from rice and wheat flour (diet DDG‐RW). In the first experiment, three replicate groups of the freshwater snails averaging 133.0 ± 2.48 mg were fed one of the experimental diets for 12 weeks. Weight gain of the juvenile freshwater snails was not affected by dietary DDG (P > 0.05). In the second experiment, three replicate groups of the juvenile abalones averaging 296.3 ± 1.73 mg were fed one of the three experimental diets for 22 weeks. Weight gain of the abalones was not affected by dietary DDG (P > 0.05). Proximate and amino acid compositions of the whole body in the freshwater snails and soft body in the abalones were not affected by dietary DDG (P > 0.05). The results of the two experiments indicated that DDG can be used as a suitable feed ingredient for partial replacement of soybean meal and wheat flour at a level of 200 g kg^?1 in diets without any adverse effects on the growth performance of freshwater snail and juvenile abalone.     

Influences of dietary distillers dried grain level on growth performance,body composition and biochemical parameters of juvenile olive flounder (Paralichthys olivaceus)

This study was conducted to investigate the influence of dietary distillers dried grain (DDG) level on growth and body composition of juvenile olive flounder (Paralichthys olivaceus). Five diets (designated as DDG0, DDG7, DDG14, DDG21 and DDG28) were prepared to contain 0, 70, 140, 210 and 280 g kg^?1 DDG. Three replicate groups of fish averaging 11.6 ± 0.1 g were fed one of the diets for 8 weeks. Weight gain of fish fed diets containing 70–280 g kg^?1 DDG was not different to that of fish fed DDG0 diet (P > 0.05). Feed efficiency of fish fed DDG21 and DDG28 diets was lower than that of fish fed DDG0 diet (P < 0.05). The antioxidant enzyme and digestive enzyme activities were not affected by dietary DDG levels. The results of this experiment suggested that DDG is a valuable ingredient as a candidate to replace wheat flour in the diet and could be used up to 280 g kg^?1 for the growth of olive flounder. On the other hand, if lower feed efficiency of fish fed 210–280 g kg^?1 DDG is considered, up to 140 g kg^?1 DDG in diet is recommended for optimum feed utilization of fish.     

Preliminary Study of the Optimum Dietary Ascorbic Acid Level in Sea Cucumber,Apostichopus japonicus (Selenka)

A 14‐wk feeding trial was carried out to evaluate the optimum dietary ascorbic acid (AA) level in juvenile sea cucumber, Apostichopus japonicus. Sea cucumbers averaging 1.49 ± 0.07 g (mean ± SD) were randomly distributed into 18 rectangular plastic tanks of 20 L capacity in a recirculating system (20 animals per tank). Six semipurified experimental diets were formulated to contain 0 (l ‐ascorbyl‐2‐monophosphate [AMP]; AMP0), 30 (AMP24), 60 (AMP48), 120 (AMP100), 240 (AMP206), and 1200 (AMP1045) mg AA/kg diet in the form of AMP using casein as the main protein source. Sea cucumbers were fed each of the six experimental diets in triplicate groups. At the end of 14 wk of feeding trial, weight gain (WG), specific growth rate (SGR), and feed efficiency (FE) of sea cucumbers fed AMP100, AMP206, and AMP1045 were significantly (P < 0.05) higher than those of animals fed AMP0, AMP24, and AMP48. However, there were no significant differences in WG, SGR, and FE among sea cucumbers fed AMP100, AMP206, and AMP1045 and among animals fed AMP0, AMP24, and AMP48. Whole‐body vitamin C concentration increased with AA content of the diets. Broken‐line analysis of WG showed an optimum dietary AA level of 105.3 mg AA/kg diet in sea cucumber. These results indicated that the optimum dietary vitamin C level in sea cucumber in the form of AMP could be greater than 100 mg AA/kg diet but less than 105.3 mg AA/kg diet.     

Effectiveness of l‐ascorbyl‐2‐polyphosphate as an ascorbic acid source for sea cucumber,Apostichopus japonicus

A feeding trial was conducted to determine the adequate dietary ascorbic acid (AsA) levels and the effects on growth, meat quality and antioxidant status of sea cucumber (10.04 ± 0.06 g), Apostichopus japonicus. l ‐ascorbyl‐2‐polyphosphate (35% AsA equivalent) was supplemented separately to the basal diet to obtain five AsA levels, 0, 598, 1473, 4676 and 14340 mg kg^?1 diet respectively. After 60‐day feeding trial, the sea cucumbers fed diets containing 598 and 1473 mg AsA kg^?1 showed significantly higher (P < 0.05) body weight gain and specific growth rate values than the sea cucumbers fed control diets. The sea cucumbers fed diets containing 1473 and 4676 mg AsA kg^?1 showed significantly higher (P < 0.05) hydroxyproline contents than those of the sea cucumbers fed diets containing 0 and 598 mg AsA kg^?1. Antioxidant enzymes such as total antioxidant capacity, superoxide dismutase and glutathione peroxidase showed increasing trends with the increasing dietary AsA levels, but no significant differences (P > 0.05) were observed when the sea cucumbers fed diets with high dietary AsA levels. The content of malondialdehyde had the opposite trend of antioxidant enzymes. In conclusion, the adequate dietary AsA level focusing on growth performance of sea cucumber is between 598 and 1473 mg kg^?1 diet. Furthermore, high level of dietary AsA (between 598 and 4676 mg kg^?1 diet) improved meat quality and antioxidant status.     

Effects of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on the growth performance,digestive enzymes and selected non‐specific immune responses in sea cucumber,Apostichopus japonicus Selenka

A feeding trial was conducted to evaluate the efficacy of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on growth performance, digestive, non‐specific immune and phagocytosis of sea cucumber, Apostichopus japonicus. Sea cucumbers (initial body weight 1.35 ± 0.04 g) were fed diets supplemented with five levels of HK L‐137 (0, 0.005, 0.025, 0.05 and 0.25 g HK L‐137 kg^?1 diets) for 60 days. Results indicated sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher body weight gain and specific growth rate than other groups. Sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher protease activity than control group. Higher amylase, lysozyme and phagocytic activities were found in 0.25 g HK L‐137 kg^?1 diet group. Higher superoxide dismutase enzyme and alkaline phosphatase activity was found in 0.05 g HK L‐137 kg^?1. While no significant differences (P > 0.05) were found in acid phosphatase activity. These results suggested that dietary supplementation of 0.05 g HK L‐137 kg^?1 diets would have benefit on growth, digestive enzymes and several non‐specific immune parameters of sea cucumber.     

Dietary selenium requirement for juvenile cobia,Rachycentron canadum L.

A 10‐week feeding trial was conducted to estimate the optimum dietary selenium (Se) requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.6% crude protein from vitamin‐free casein, gelatin. A control diet (no added seleno‐dl ‐methionine) and five experimental diets containing 0.20, 0.40, 0.60, 0.80 and 1.00 mg seleno‐dl ‐methionine kg^?1 were prepared. Each diet was randomly fed to triplicate groups of juvenile cobia with initial weight 6.27±0.03 g in a flow‐through system. The Se concentration in rearing water was monitored during the feeding period, and was not detectable. The dietary Se level significantly influenced the survival, specific growth rate (SGR), feed efficiency and the Se concentrations in the whole body and vertebra of cobia. The Se‐dependent glutathione peroxidase (EC 1.11.119) activity increased with an increase in the dietary Se levels (P<0.05). Hepatic glutathione reductase (EC 1.6.4.2) activity was the highest in fish fed the diet with 0.21 mg Se kg^?1, and declined with an increase in the dietary Se levels. Based on broke‐line regression of SGR, the Se concentration in the whole body and vertebra, the Se requirements of juvenile cobia were 0.788, 0.811 and 0.793 mg Se kg^?1 diet in the form of seleno‐dl ‐methionine respectively.     

Effects of dietary ethoxyquin on growth,feed utilization and residue in the muscle of juvenile Japanese seabass,Lateolabrax japonicus

Ethoxyquin (EQ) is the most common synthetic antioxidant used for preventing rancidity in fish foodstuffs. However, literature related to the effects of dietary EQ on performance of fish was limited. The present study was conducted to investigate the effects of EQ on performance and EQ residue in muscle of juvenile Japanese seabass Lateolabrax japonicus and to estimate the optimal EQ concentration in the diet. Graded levels [0 (control), 50, 150, 450 and 1350 mg EQ kg^?1 diet] of EQ were added to the basal diet, resulting in five dietary treatments in the experiment. Each diet was fed to triplicate groups of seabass (initial body weight 8.01 ± 0.76 g) for 12 weeks in floating sea cages (1.5 × 1.5 × 2.0 m, 30 fish per cage). Survival ranged from 78.9 to 86.7%, and was irrespective of dietary EQ levels. The specific growth rate (SGR) of fish fed diets supplemented with ≤50 mg kg^?1 EQ had significantly (P < 0.05) higher SGR than fish fed diets supplemented with ≥150 mg kg^?1 EQ, the highest SGR was observed in fish fed diet with 50 mg kg^?1 EQ supplementation. Feed intake (FI) and feed efficiency (FE) were not significantly (P > 0.05) different among dietary treatments. Fish fed diets with 50 and 1350 mg kg^?1 EQ had a significant (P < 0.05) lower body lipid content than fish in the control group. Muscle EQ level significantly increased when dietary EQ increased. Optimal EQ concentration estimated by polynomial regression based on maximum growth of juvenile Japanese seabass was 13.78 mg kg^?1 diet.     

Quantitative l‐lysine requirement of juvenile black sea bream (Sparus macrocephalus)

An 8‐week feeding experiment was conducted to determine the quantitative l ‐lysine requirement of juvenile black sea bream Sparus macrocephalus (initial mean weight: 9.13 ± 0.09 g, SD) in eighteen 300‐L indoors flow‐through circular fibreglass tanks provided with sand‐filtered aerated seawater. The experimental diets contained six levels of l ‐lysine ranging from 20.8 to 40.5 g kg^?1 dry diet at about 4 g kg^?1 increments. All the experiment diets were formulated to be isoenergetic and isonitrogenous. Each diet was assigned to triplicate groups of 20 fish in a completely randomized design. Weight gain and specific growth rate (SGR) increased with increasing levels of dietary lysine up to 32.5 g kg^?1 (P < 0.05) and both showed a declining tendency thereafter. Feed efficiency ratio and protein efficiency ratio was poorer for fish fed the lower lysine level diets (P < 0.05) and showed no significant differences among other treatments (P > 0.05). All groups showed high survival (above 90%) and no significant differences were observed. The whole body crude protein and crude lipid contents were significantly affected (P < 0.05) by dietary lysine level, while moisture and ash showed no significant differences. The composition of muscle and liver also presented similar change tendency. Total essential amino acid and lysine contents in muscle both obtained the highest value when fish fed 32.5 g kg^?1 lysine diet (P < 0.05). Serum protein, cholesterol and free lysine concentration were affected by different dietary treatments (P < 0.05), triacylglyceride and glucose contents were more variable and could not be related to dietary lysine levels. Dietary lysine level significantly affected condition factor and intraperitoneal fat ratio of juvenile black sea bream (P < 0.05) except for hepatosomatic index. There were no significant differences in white blood cell count and red blood cell count (P > 0.05), however, haemoglobin level was significantly influenced by different diets (P < 0.05). Analysis of dose (lysine level)‐response (SGR) with second order polynomial regression suggested the dietary lysine requirement of juvenile black sea bream to be 33.2 g kg^?1 dry diet or 86.4 g lysine kg^?1 protein.     

Effects of dietary lipid level on growth performance,body composition and digestive enzymes activity of juvenile sea cucumber,Apostichopus japonicus

A feeding trial aimed to determine the effects of dietary lipid level on growth performance, body composition and digestive enzymes activity of juvenile sea cucumber, Apostichopus japonicus. Diets with six crude lipid levels (1.9, 13.8, 29.1, 43.6, 59.6 and 71.6 g kg^?1) were fed to sea cucumbers (initial weights 0.65 ± 0.01 g) at a density of 30 juveniles, once a day. After 60 days, body weight gain (BWG), specific growth rate (SGR), feed intake (FI) and protein efficiency ratio (PER) decreased with increasing dietary lipid levels. The sea cucumbers fed 1.9 g kg^?1 crude lipid showed significantly higher (P < 0.05) BWG than those of the sea cucumbers fed 59.6 and 71.6 g kg^?1 crude lipid. Intestinal protease and lipase activities generally increased with increasing dietary lipid levels. Eicosapentaenoic acid (EPA) content of body walls generally increased with increasing dietary lipid levels. Docosahexaenoic acid (DHA) content of body walls reached the maximum value at a dietary lipid level of 13.8 g kg^?1. N‐3 highly unsaturated fatty acid content followed the same pattern of DHA. According to the growth performance and body composition of sea cucumbers, it can be indicated that the optimum dietary lipid level for juvenile sea cucumbers is between 1.9 and 13.8 g kg^?1.     

Growth,body composition,intestinal enzyme activities and microflora of juvenile Jian carp (Cyprinus carpio var. Jian) fed graded levels of dietary phosphorus

A 9‐week feeding trial was carried out with juvenile Jian carp (Cyprinus carpio var. Jian) to study the effects of dietary phosphorus on growth, body composition, intestinal enzyme activities and microflora. Quadruple groups of juvenile Jian carp (7.17 ± 0.01 g) were fed practical diets containing available phosphorus 1.7 (unsupplemented control), 3.6, 5.5, 7.3, 9.2 and 11.0 g kg^?1 diet to satiation. Feed intake, specific growth ratio and feed efficiency were the lowest in fish fed the basal diet (P < 0.05). Body moisture, protein, lipid content and ash were all significantly affected by dietary available phosphorus levels (P < 0.05). Activities of trypsin, amylase, Na⁺, K⁺‐ATPase, alkaline phosphatase and gamma‐glutamyl transpeptidase were improved with increasing dietary phosphorus levels. Intestinal Aeromonas and Escherichia coli decreased with increasing dietary phosphorus up to 3.6 and 5.5 g kg^?1 diet respectively (P < 0.05), while Lactobacillus increased with the increasing dietary phosphorus up to 9.2 g kg^?1 diet (P < 0.05). These results suggested that phosphorus could enhance intestinal enzyme activities of juvenile Jian carp and the minimum dietary available phosphorus requirement for SGR of juvenile Jian carp (7.2–63.8 g) was 5.2 g kg^?1 diet.     

Quantitative l-lysine requirement of juvenile grouper Epinephelus coioides

An 8‐week feeding trial was conducted to determine the quantitative lysine requirement of juvenile grouper Epinephelus coioides (initial mean weight: 15.84 ± 0.23 g, mean ± SD) in eighteen 500‐L indoors flow‐through circular fibreglass tanks provided with sand‐filtered aerated seawater by feeding diets containing six levels of l ‐lysine ranging from 19.2 to 39.5 g kg^?1 dry diet in 4 g kg^?1 increments. The diets, in which 250 g crude protein kg^?1 diet came from fish meal and soybean protein concentrate, and 230 g kg^?1 from crystalline amino acids, were formulated to simulate the amino acid profile of 480 g kg^?1 whole chicken egg protein except for lysine. Each diet was assigned to three tanks in a completely randomized design. Grouper were fed to apparent satiation twice daily during the week and once daily on weekends. Weight gain and specific growth rate increased with increasing levels of dietary lysine up to 27.2 g kg^?1 (P < 0.05) and remained nearly the same thereafter (P > 0.05). Feed efficiency was the poorest for fish fed the lowest lysine diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Survival could not be related to dietary treatments. Body composition remained relatively constant except for lipid contents in muscle and liver. Total essential amino acid contents in liver increased with dietary lysine level although there was a slight decline for fish fed the highest lysine level of diet. Plasma protein content increased with increasing dietary lysine level (P < 0.05), but cholesterol, triacylglycerol and glucose contents were more variable and could not be related to dietary treatments. Dietary lysine level significantly influenced morphometrical parameters (condition factor, hepatosomatic index and intraperitoneal fat ratio) of juvenile grouper (P > 0.05). Broken‐line analysis of weight gain indicated the dietary lysine requirement of juvenile grouper to be 28.3 g kg^?1 diet or 55.6 g kg^?1 dietary protein.     

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.     

Dietary l‐methionine requirement of juvenile black sea bream (Sparus macrocephalus) at a constant dietary cystine level

An 8‐week feeding trial was conducted to determine the effects of dietary methionine level on juvenile black sea bream Sparus macrocephalus. Fish (initial body weight: 14.21 ± 0.24 g) were reared in eighteen 350‐L indoors flow‐through circular fibreglass tanks (20 fish per tank). Isoenergetic and isonitrogenous diets contained six levels of L‐methionine ranging from 7.5 to 23.5 g kg⁻¹ of dry diet in 3.0 g kg⁻¹ increments at a constant dietary cystine level of 3.1 g kg⁻¹. Growth performance and feed utilization were significantly influenced by dietary methionine levels (P < 0.05). Maximum weight gain (WG), specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value (PPV) occurred at 17.2 g methionine kg⁻¹ diet, beyond which they showed declining tendency. Protein contents in whole fish body and dorsal muscle were positively correlated with dietary methionine level, while muscle lipid content was negatively correlated with it. Apparent digestibility coefficients (ADCs) of dietary nutrients were significantly affected by dietary treatments except for ADCs of crude lipid. Fish fed the grade level of methionine demonstrated a significant improvement in whole‐body methionine content, total essential amino acids (∑EAA), total non‐essential amino acids (∑NEAAs) and ∑EAA/∑NEAA ratio (P < 0.05). Regarding serum characteristics, significant differences were observed in total cholesterol, glucose and free methionine concentration (P > 0.05), while total protein level and triacylglycerol concentration kept relatively constant among treatments (P < 0.05). Analysis of dose response with second‐order polynomial regression on the basis of either SGR or PPV, the optimum dietary methionine requirements of juvenile black sea bream were estimated to be 17.1 g kg⁻¹ of diet (45.0 g kg⁻¹ methionine of protein) and 17.2 g kg⁻¹ of diet (45.3 g kg⁻¹ methionine of protein) in the presence of 3.1 g kg⁻¹ cystine, respectively.     

Optimum Level of Dietary n‐3 Highly Unsaturated Fatty Acids for Juvenile Sea Cucumber,Apostichopus japonicus

A feeding trial was conducted to estimate the optimum level of dietary n‐3 highly unsaturated fatty acids (HUFAs) for juvenile sea cucumber, Apostichopus japonicas, based on growth performance and fatty acid compositions. Diets with five n‐3 HUFAs levels (0.15, 0.22, 0.33, 0.38, and 0.46%) were fed to sea cucumber juveniles (1.97 ± 0.01 g) once a day for 60 d. The sea cucumbers fed diets containing 0.22% n‐3 HUFAs showed significantly (P < 0.05) higher body weight gain, feed efficiency, and protein efficiency ratio than the sea cucumbers fed diets containing 0.15% n‐3 HUFAs, but not significantly different (P > 0.05) from those of sea cucumbers fed diets containing 0.33, 0.38, and 0.46% n‐3 HUFAs. The sea cucumbers fed diets containing 0.46% n‐3 HUFAs showed significantly (P < 0.05) higher eicosapentaenoic acid and saturated fatty acid than the sea cucumber fed diets containing 0.15% n‐3 HUFAs, but not significantly different (P > 0.05) from those of sea cucumbers fed diets containing 0.22, 0.33, and 0.38% n‐3 HUFAs. The results of growth performance and n‐3 HUFA compositions of body wall indicated that the optimum level of dietary n‐3 HUFAs for juvenile sea cucumber is between 0.22 and 0.46%.     

The growth performance of southern catfish fed diets with raw, precooked cornstarch and glucose at two levels

The ability of juvenile carnivorous southern catfish (Silurus meridionalis Chen) to use different levels, kinds and physic state (glucose, raw cornstarch and precooked cornstarch) of dietary carbohydrate was evaluated in term of growth performance. All diets contained 100 g kg^?1 lipid and 16 kJ metabolizable energy. Three isonitrogeneus (400 g kg^?1) diets were formulated to contain 150 g kg^?1 raw cornstarch, precooked cornstarch and glucose. Another three isonitrogeneus (300 g kg^?1) diets were formulated to contain 300 g kg^?1 raw cornstarch, precooked cornstarch and glucose. A control diet was formulated with no carbohydrate containing 500 g kg^?1 protein. Each experimental diet was fed to four tanks of 10 fish (28.3 ± 0.5 g) for 8 weeks at 27.5 °C. Specific growth rate (SGR) of 300 g kg^?1 glucose diet was significantly lower than those of other diets (P < 0.05). Feeding rates (FR) of 300 g kg^?1 glucose and control diets were significantly lower than those of the other diets (P < 0.05). Feed efficiency (FE) was significantly decreased with increased dietary carbohydrate level (P < 0.05). Feed efficiency of the 300 g kg^?1 glucose diet was significantly lower than those of the 300 g kg^?1 raw and precooked cornstarch diets (P < 0.05). The protein efficiency ratio (PER) was significantly increased with dietary carbohydrate level except that of the 300 g kg^?1 glucose diet, which was lowest among all diets (P < 0.05). The results suggested that both dietary starch and glucose were utilized for energy in southern catfish and had a protein‐sparing effect. At 150 g kg^?1 inclusion level, the utilization of raw and precooked cornstarch and glucose did not vary significantly, but a higher dietary glucose level (300 g kg^?1) had a markedly detrimental effect on growth in southern catfish.     

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.     

Dietary arginine requirement of juvenile swimming crab,Portunus trituberculatus

An 8‐week feeding trial was conducted to determine the optimal dietary arginine requirement for juvenile swimming crab Portunus trituberculatus. Six isonitrogenous and isolipidic experimental diets were formulated to contain graded arginine levels which ranged from 15.9 to 33.0 g kg^?1. Each diet was randomly assigned to triplicate groups of 60 juvenile swimming crabs (4.72 ± 0.12 g). The results indicated that dietary arginine had significant effects on weight gain (WG), specific growth rate (SGR), protein productive value, feed efficiency and protein efficiency ratio. Weight gain and SGR significantly increased with the dietary arginine increasing from 15.9 to 27.4 g kg^?1, while with the further increasing from 27.4 to 33.0 g kg^?1, WG and SGR did not increase significantly. Maximum arginine, proline and total essential amino acid contents in muscle were observed in 27.4 g kg^?1 group diet. The swimming crab fed the diet with lower dietary arginine level showed higher AST and lower ALT in the serum. Crab fed with the lower dietary arginine level had significantly lower ALT in the serum than the other groups. Haemolymph indexes were significantly affected by the dietary arginine level except for the cholesterol concentration, and the highest values were all found in 27.4 g kg^?1 group diet. The two slope broken‐line model using SGR showed that the optimal dietary arginine requirement was 27.7 g kg^?1 of the dry matter (56.0 g kg^?1 dietary protein) for juvenile swimming crab.     

Optimal dietary lipid level for large yellow croaker (Pseudosciaena crocea) larvae

A 30‐day feeding experiment was conducted in blue tanks (70 × 50 × 60 cm, water volume 180 L) to determine the effects of dietary lipid levels on the survival, growth and body composition of large yellow croaker (Pseudosciaena crocea) larvae (12 days after hatchery, with initial average weight 1.93 ± 0.11 mg). Five practical microdiets, containing 83 g kg^?1 (Diet 1), 126 g kg^?1 (Diet 2), 164 g kg^?1 (Diet 3), 204 g kg^?1 (Diet 4) and 248 g kg^?1 lipid (Diet 5), were formulated. Live feeds (Artemia sinicia nauplii and live copepods) were used as the control diet (Diet 6). Each diet was randomly assigned to triplicate groups of tanks, and each tank was stocked with 3500 larvae. During the experiment, water temperature was maintained at 23(±1) °C, pH 8.0 (±0.2) and salinity 25 (±2) g L^?1. The results showed that dietary lipid significantly influenced the survival and growth of large yellow croaker larvae. Survival increased with the increase of dietary lipid from 83 to 164 g kg^?1, and then decreased. The survival of larvae fed the diet with 83 g kg^?1 lipid (16.1%) was significantly lower than that of larvae fed other diets. However, the survival in larvae fed the diet with 16.4 g kg^?1 lipid was the highest compared with other artificial microdiets. Specific growth rate (SGR) significantly increased with increasing dietary lipid level from 83 to 164 g kg^?1 (P < 0.05), and then decreased. The SGR in larvae fed the diet with 164 g kg^?1 lipid (10.0% per day) was comparable with 204 g kg^?1 lipid (9.6% per day), but were significantly higher than other microdiets (P < 0.05). On the basis of survival and SGR, the optimum dietary lipid level was estimated to be 172 and 177 g kg^?1 of diet using second‐order polynomial regression analysis respectively.     

A study on dietary l‐lysine requirement of juvenile yellow catfish Pelteobagrus fulvidraco

An 8‐week feeding trial was conducted to determine lysine requirement of juvenile yellow catfish (Pelteobagrus fulvidraco) by feeding formulated diets containing crystalline l ‐lysine. Six isonitrogenous and isoenergetic diets (405 g kg^?1 protein, 18 kJ g^?1 gloss energy) containing fish meal together with soybean protein concentrate as protein sources and fish oil together with soybean oil as lipid sources were formulated. Crystalline l ‐lysine was added into the six diets to acquire lysine concentrations of 17.3, 21.8, 26.0, 31.3, 35.5 and 41.9 g kg^?1 dry diets, respectively. Mixture of crystalline amino acid was supplemented to simulate the amino acid profile in muscle of yellow catfish. The results indicated that final body weight (FBW), weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency (PE) increased with the increase in dietary lysine level from 17.3 to 31.3 g kg^?1 of diet and then decreased as the dietary lysine levels further increased. No significant difference in survival rate was found among all the dietary treatments. One‐slope, quadratic broken‐line analysis on the basis of SGR showed that the dietary l ‐lysine requirement of juvenile yellow catfish was 33.1 g kg^?1 of dry diet (83.2 g kg^?1 of dietary protein).