Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.     

Dietary vitamin C requirement of red drum Sciaenops ocellatus

A feeding trial was conducted to determine the minimum dietary vitamin C requirement of juvenile red drum and characterize signs of vitamin C deficiency. Semipurified diets containing 400 g crude protein kg^–1 from lyophilized red drum muscle and crystalline amino acids were used in the feeding trial. The basal diet without supplemental vitamin C contained ≈ 6 mg vitamin C kg^–1 and was fed for a 1-week conditioning period. Red drum, initially averaging ≈ 3.6 g each, were fed diets supplemented with 0, 10, 20, 30, 45, 60, 75, or 150 mg vitamin C kg^–1 as ascorbate polyphosphate for a period of 10 weeks. Fish fed the basal diet began to exhibit overt signs of vitamin C deficiency, including reduced weight gain, lordosis, scoliosis and loss of equilibrium after 8 weeks. Total ascorbate was undetectable in liver of fish fed the basal diet while liver ascorbate levels in fish fed the other diets generally reflected dietary supplementation. Regression analysis of weight gain data using the broken-line model resulted in a minimum vitamin C requirement ( ± SE) of 15 ± 3 mg kg^–1 diet.     

Effects of dietary vitamin E supplementation on growth performance, lipid peroxidation and tissue fatty acid composition of black sea bream (Acanthopagrus schlegeli) fed oxidized fish oil

A 9-week feeding experiment was conducted to evaluate the effects of dietary vitamin E supplementation on growth, lipid peroxidation and fatty acid composition of black sea bream fed oxidized oil. The FL and OL diets contained fresh fish oil and oxidized oil, respectively, without additional vitamin E supplementation. Another four α-tocopherol levels (150, 250, 450 and 800 mg kg⁻¹ diet) were used within the OL diet, giving a total of six experimental diets. Fish were hand-fed to apparent satiation twice daily. At end of the trial, the weight gain and survival rate of fish were significantly reduced by diets with oxidized oil, whereas hepatosomatic index was remarkably high in fish fed oxidized oil diet. However, vitamin E supplementation to diet significantly improved growth performance and increased vitamin E content in the liver. Although, liver thiobarbituric acid reactive substances and docosahexaenoic acid were significantly increased by dietary oxidized oil, their levels were reduced by dietary vitamin E supplementation. Our results indicate that the fish were performing the best at intermediate concentrations of α-tocopherol and a dose of >150 mg α-tocopherol kg⁻¹ diet could reduce lipid peroxidation and improve fish growth performance when oxidized oils exist in diet.     

Effect of dietary lipid level on muscle composition in Atlantic salmon Salmo salar

This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg^–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg⁻¹ or the 470 g kg⁻¹ lipid diets compared with the 310 g kg⁻¹ lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg⁻¹ lipid diet, and to 16 ± 2% in salmon fed the 380 g kg⁻¹ and 470 g kg⁻¹ lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg⁻¹ lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.     

Re-evaluation of vitamin E supplementation of practical diets for channel catfish, Ictalurus punctatus, production

A 10-month feeding trial was performed with channel catfish, Ictalurus punctatus , to re-evaluate the minimum level of dietary vitamin E supplementation required under conditions of commercial production. Four levels (0, 15, 30 and 60 mg kg⁻¹ diet) of supplemental vitamin E were added as DL -α-tocopherol acetate to a typical commercial catfish diet. Sixteen 0.04-ha ponds were stocked in July, at a rate of 25 000 fish ha⁻¹, with two size classes (averaging 18 and 265 g fish⁻¹) of fingerling channel catfish, and each diet was fed to fish in four replicate ponds once daily to satiation. After 10 months of feeding, a total harvest was performed to obtain final production data, and samples were obtained from fish in all ponds. Liver and plasma samples were obtained for α-tocopherol determination, and liver, heart and muscle samples were processed for histological evaluation.
No discernible differences occurred among fish fed the different diets with respect to weight gain or survival. Mean production rate was 9734 kg ha⁻¹, with a final average fish weight of 0.53 kg. A significant ( P < 0.05) effect of diet was noted in plasma and liver α-tocopherol levels, which increased with dietary supplementation. An effect of size also was apparent, with plasma and liver α-tocopherol levels being higher in larger fish compared with smaller fish within a dietary treatment. Histological evaluation revealed no differences among fish fed the different dietary treatments. Based on the lack of overt histological signs of deficiency, it appears that the current level of vitamin E supplementation of commercial catfish diets may be reduced considerably with no detriment to channel catfish health or production.     

Dietary threonine requirement of juvenile hybrid striped bass (Morone chrysops♀×M. saxatilis♂)

Two growth studies were conducted to determine the dietary threonine requirement of reciprocal cross hybrid striped (sunshine) bass. Semipurified diets were prepared with crystalline amino acids and lyophilized fish muscle to supply 350 g crude protein kg⁻¹ diet. The basal diet contained 4.9 g threonine kg⁻¹ from fish muscle, and test diets were supplemented with graded levels of L-threonine. In the first experiment, fish initially averaging ≊ 9.8 g each were fed diets containing threonine levels of 4.9, 7.5, 10.0, 12.5, 15.0 and 17.5 g kg⁻¹ dry diet for 7 weeks. Weight gain, feed efficiency and protein efficiency ratio (PER) were significantly ( P < 0.01) influenced by dietary threonine level. Based on weight-gain responses, a threonine requirement (± SE) of 8.4 (± 0.8) g kg⁻¹ dry diet was determined, and dietary threonine levels of 10.0 g kg⁻¹ diet or greater resulted in the highest levels of free threonine in plasma.
Based on the results of the first experiment, a second feeding trial was conducted with diets containing threonine levels of 4.9, 6.5, 8.0, 9.5, 11.0 and 12.5 g kg⁻¹ dry diet. Fish initially averaging ≊ 3.0 g each were fed each diet for 8 weeks. Weight gain, feed efficiency and PER values of fish were markedly improved, with increases in dietary threonine up to 8.0 g kg⁻¹ dry diet. Regression analysis of weight gain, feed efficiency and PER data using the broken-line model resulted in threonine requirement estimates of 9.7, 8.5 and 8.6 g kg⁻¹ dry diet, respectively. Based on these data, the threonine requirement of juvenile sunshine bass was determined to be ≊ 9.0 g kg⁻¹ dry diet or 26 g kg⁻¹ of dietary protein.     

Interaction between dietary levels of vitamins C and E on growth and immune responses in channel catfish, Ictalurus punctatus (Rafinesque)

This study was conducted to evaluate the effect of dietary levels of vitamins C (0, 100 and 2000 mg kg⁻¹), E (0, 50 and 500 mg kg⁻¹) and their interaction on the growth performance, liver contents of ascorbic acid and α-tocopherol, haematology and immune response of channel catfish, Ictalurus punctatus . Each diet was fed to catfish in triplicate aquaria to apparent satiation twice daily for 12 weeks. The results indicate that the amount of vitamin E contained in the basal diet (23.1 mg kg⁻¹) was sufficient to promote good growth, feed efficiency and survival, but its supplementation was needed to maintain high haematological values and liver vitamin E. Supplementation of vitamin C (100 mg kg⁻¹) to the basal diet containing 10.5 mg kg⁻¹ was required for good growth, feed efficiency, survival and prevention of vertebral deformity and optimum haematological indices. Liver storage of ascorbic acid and α-tocopherol increased with increasing dietary levels of each vitamin. Dietary vitamin E levels had no effect on liver ascorbic acid content, but increasing dietary vitamin C increased liver α-tocopherol. Some measured immune parameters (serum protein and superoxide anion production) were enhanced by supplementation of vitamin C or E. Chemotaxis ratio and phagocytosis were not affected by treatments.     

Selenium nutrition of hybrid striped bass (Morone chrysops × M. saxatilis) bioavailability, toxicity and interaction with vitamin E

Two concurrent 12-week feeding trials were conducted to evaluate the bioavailability of inorganic sodium selenite and organic seleno-DL-methionine and to investigate the potential interaction between selenium and vitamin E in juvenile hybrid striped bass. In experiment 1, purified diets utilizing casein, gelatin and an amino acid premix as protein sources with a basal selenium concentration of 0.11 mg Se   kg⁻¹ were supplemented with either Na₂SeO₃ to provide selenium concentrations of 1.19, 2.00, 5.17 and 21.23 mg Se kg⁻¹ or with seleno-DL-methionine to provide 0.90, 1.26 and 2.55 mg Se kg⁻¹ and fed to juvenile hybrid striped bass in aquaria. A second experiment evaluated potential interactions by feeding these purified diets with or without supplemental vitamin E or sodium selenite, singularly or in combination. No overt selenium deficiency signs were exhibited by fish in either of the experiments; however, signs of selenium toxicity including retarded weight gain (WG), reduced feed intake and feed efficiency ratio (FER) as well as increased mortality, were observed in fish fed the diet containing more than 20 mg Se kg⁻¹. Whole-body selenium and whole-body selenium retention were linearly influenced by sodium selenite and selenomethionine. However, there was no significant effect of dietary selenium, vitamin E or their interaction on WG, FER and survival. Slope-ratio analysis showed that bioavailability of seleno-DL-methionine as a selenium source for juvenile hybrid striped bass was significantly ( P  < 0.01) higher (3.3-fold) than sodium selenite.     

Effects of dietary protein to metabolizable energy ratios and total protein concentrations on the performance of yellow perch Perca flavescens

Juvenile yellow perch Perca flavescens were fed semipurified diets with varying protein to metabolizable energy ratios (PME, g protein MJ⁻¹ metabolizable energy) and nutrient densities in three experiments to determine recommended dietary protein and energy concentrations. Experiment 1 fish (18.6 g) were fed diets containing 450 g crude protein kg⁻¹ dry diet and 14.5–18.8 MJ ME kg⁻¹ dry diet for 10 weeks. No differences were found in the growth of experiment 1 fish fed the different diets. Experiment 2 fish (21.9 g) were fed diets containing 15.7 MJ ME kg⁻¹ dry diet and 210–420 g crude protein kg⁻¹ dry diet for 8 weeks. Fish fed the diet containing 340 g kg⁻¹ protein (diet PME = 22) exhibited the greatest weight gain. Experiment 3 fish (27.1 g) were fed diets with a PME of 22 and varying nutrient density (yielding 205–380 g crude protein kg⁻¹ dry diet) for 8 weeks. No differences were found in the growth of experiment 3 fish. Yellow perch fed the semipurified diets exhibited increased liver fat content, liver size and degree of liver discoloration compared with fish fed a commercial fish meal-based diet. Liver changes may have resulted from high dietary carbohydrate levels. We conclude that a protein level of 210–270 g kg⁻¹ dry diet is suitable for juvenile yellow perch provided that the dietary amino acid profile and carbohydrate content are appropriate for yellow perch.     

Effects of dietary phosphorus level on non-faecal phosphorus excretion from yellowtail (Seriola quinqueradiata Temminck & Schlegel) fed purified and practical diets

Non-faecal phosphorus (P) was determined for large yellowtail to estimate a minimum available P requirement (Experiment  1) and to justify inorganic P supplementation in a fish meal-based diet (Experiment 2). In Experiment 1, purified diets with incremental P concentrations were fed to yellowtail (mean weight 917 g) at a feeding rate of 1.5% of body weight. The peaks of non-faecal P excretion appeared 5–6 h after feeding in fish fed more than 4.5 g available P kg⁻¹ dry diet. Broken-line analysis indicated that the minimum available P requirement was 4.4 g kg⁻¹ dry diet. In Experiment 2, a purified diet (PR) containing 6.5 g available P kg⁻¹ and a fish meal-based diet with (F1) and without (F0) additional phosphorus were fed to yellowtail (mean weight 1.1 kg) at 1.5% (PR) and 2% (F0 and F1) feeding rates respectively. There was no significant difference in P excretion between fish fed the F0 (5.5 g soluble P kg⁻¹ dry diet) and the PR diet. However, significantly higher (34.5%) amounts of non-faecal P excretions (7.4 g soluble P kg⁻¹ dry diet) were found in fish fed F1 compared with the F0 diet. This suggested that there was an excess of dietary P in the F1 diet and that supplementation is not needed in fish meal-based diets for large yellowtail.     

Effects of digestible protein levels in isonitrogenous diets on growth performance and tissue composition of juvenile Atractoscion nobilis

A study was undertaken to estimate the effects of isonitrogenous diets (ca. 604 g kg⁻¹ crude protein) containing formaldehyde-treated (FT) fish meal and graded levels of digestible protein (DP) (541, 491, 372, 347 and 247 g kg⁻¹) on growth performance and tissue composition of juveniles white seabass. Five diets were formulated to contain increasing levels of FT fish meal (from 0 to 384 g kg⁻¹) and decreasing levels of non-treated fish meal (from 480 to 96 g kg⁻¹). Each dietary treatment was fed in triplicate to apparent satiation to groups of 25 fish for 50 days. Significantly higher growth performance and feed conversion ratio were obtained in fish-fed diets containing 491 or 541 g kg⁻¹ DP, compared with all other treatments. Apparent digestibility coefficient of protein in the diets was not significantly affected by the inclusion of treated fish meal in the diets. Estimation of protein requirements using a broken-line regression analysis indicated that maximum weight gain would be obtained with a diet containing 503 ± 23 g kg⁻¹ DP. The results from this study suggest that a single-diet formulation using protein treated with formaldehyde as filler might be useful to estimate the requirement of DP for fish.     

RRR-α-Tocopheryl succinate is a less bioavailable source of vitamin E than all-rac-α-tocopheryl acetate for red drum, Sciaenops ocellatus

Bioavailability of the succinate ester of α-tocopherol has never been investigated with aquatic animals to date. Therefore, a 12-week feeding trial was conducted to compare bioavailability of α-tocopheryl acetate and α-tocopheryl succinate by slope ratio analysis. The semi-purified diets were supplemented with either 0 (basal), 10, 20 and 40 IU vitamin E/kg as all-rac-α-tocopheryl acetate or 10, 20, or 40 IU vitamin E/kg as RRR-α-tocopheryl succinate. Red drum juveniles were conditioned by feeding the basal diet for 8 weeks prior to the experimental period to reduce whole-body tocopherols. Fish initially averaging 12.2 ± 0.4 g/fish (mean ± SD) were fed experimental diets at a rate approaching apparent satiation for 12 weeks. Weight gain and feed efficiency responses of fish fed diets were not significantly altered by the type or level of vitamin E supplemented. However, α-tocopherol levels in liver and plasma were significantly (P < 0.01) influenced by dietary vitamin E level and ester form. The liver retention of α-tocopheryl acetate was 14 times higher than α-tocopheryl succinate, while thiobarbituric acid reactive substances (TBARS) in liver of fish fed α-tocopheryl acetate tended to be (P < 0.1) lower than that of fish fed α-tocopheryl succinate. In addition, plasma ascorbic acid in fish fed graded levels of α-tocopheryl acetate was significantly higher than fish fed graded levels of α-tocopheryl succinate. Fish fed the basal diet and 10 IU α-tocopheryl succinate/kg showed edema in the heart, while fish fed all other diets did not exhibit this pathology. Within the dose range of 0–40 IU/kg diet, hematocrit, neutrophil oxidative radical production and intracellular superoxide anion production of head kidney macrophages were not significantly influenced by α-tocopherol ester or dietary supplementation level. In conclusion, α-tocopheryl succinate is not readily available to juvenile red drum compared to the widely used α-tocopheryl acetate.     

Nutrient values of dietary ascorbic acid (l-ascorbyl-2-polyphosphate) on growth, survival and stress tolerance of larval shrimp, Litopenaeus vannamei

l -ascorbyl-2-polyphosphate (ApP) was used as a vitamin C source to investigate the ascorbic acid (AsA) requirements on growth performance and stress resistance of the larval white shrimp, Litopenaeus vannamei . Five isoenergetic and isonitrogenous fish meal-fish protein hydrolysate-based diets with five levels of ApP, AsA equivalent to 91.8, 188, 271, 360 and 436 mg kg⁻¹ diet were fed to triplicate groups of L. vannamei (mean initial wet weight 1 mg) for 32 days. The diet with AsA 91.8 mg kg⁻¹ showed high cumulative mortality after 10 days of feeding. After the 32-day trial, the shrimp that fed the diet had significantly lower survival and weight gain (WG, %) than those that fed 188, 271, 360 and 436 mg AsA kg⁻¹ diets. Specific growth rate (SGR, % day⁻¹) and final body wet weight (FBW, mg) showed the same pattern as WG (%). There were no significant differences in growth performance (FBW, WG and SGR) among the groups that fed 188, 271, 360 and 436 mg kg⁻¹ of AsA at the termination of feeding trial. Broken-line regression analysis on WG indicated that 191 mg AsA kg⁻¹ in the diet was the optimum for larval L. vannamei . On the contrary, dietary level of more than 360 mg AsA kg⁻¹ was needed to ensure high resistance to stressful conditions such as low dissolved oxygen stressors.     

Myo-inositol prevents oxidative damage, inhibits oxygen radical generation and increases antioxidant enzyme activities of juvenile Jian carp (Cyprinus carpio var. Jian)

This study was conducted to evaluate the effects of dietary myo -inositol (MI) on the antioxidant status of juvenile Jian carp ( Cyprinus carpio var. Jian). A total of 1050 Jian carp (22.28±0.07 g) were randomly distributed into seven groups of three replicates each, feeding diets containing graded levels of MI (163.5, 232.7, 384.2, 535.8, 687.3, 838.8 and 990.3 mg kg⁻¹ diet) for 60 days. Results indicated that the malondialdehyde content was the lowest for fish fed diets containing ≥384.2 mg MI kg⁻¹, and the highest for fish fed the MI-unsupplemented basal diet ( P <0.05). The protein carbonyl content was decreased with increasing dietary MI levels up to 535.8 mg kg⁻¹ diet, and no differences were found with a further increase in the MI concentration. The anti-superoxide anion capacity (ASA) and anti-hydroxyl radical capacity (AHR) were increased with increasing MI levels up to 535.8 mg kg⁻¹ diet, and plateaued thereafter. The superoxide dismutase and glutathione- S -transferase activities showed the same tendency with the ASA capacity. Catalase, glutathione peroxidase and glutathione reducase activities were improved with increasing MI levels up to 838.8, 384.2 and 687.3 mg kg⁻¹ diet, respectively, and remained nearly constant thereafter. These results suggested that MI could inhibit oxygen radical generation, increase enzymatic antioxidant capacity and prevent oxidative damage of carp. Dietary MI requirements for ASA and AHR activities of juvenile Jian carp were 567.94 and 517.22 mg MI kg⁻¹ diet respectively.     

The influence of dietary phospholipid level on the performances of juvenile amberjack, Seriola dumerili, fed non-fishmeal diets

The objective of the present study was to investigate the effect of dietary phospholipid (PL) level on growth and feed intake of juvenile amberjack ( Seriola dumerili ) fed non-fishmeal (non-FM) diet containing alternative protein sources; soybean protein isolate, tuna muscle by-product powder and krill meal. Three non-FM diets were prepared to contain three levels (14, 37 and 54 g kg⁻¹ dry diet) of PL (soybean lecithin acetone insoluble, 886 g kg⁻¹) and growth performance was monitored in a 30-day growth trial by using 2.6 g of fish. The results indicated that final body weight, weight gain and feed intake significantly increased with increasing dietary PL level. At the highest dietary PL level (54 g kg⁻¹ dry diet), the fish consumed 14.8% and 10.2% as much feed as those fish fed diets containing 14 g kg⁻¹ dry diet and 37 g kg⁻¹ dry diet PL, respectively. An increasing tendency with increasing dietary PL level on feed efficiency was observed. In conclusion, the present study demonstrated that dietary PL supplementation could increase feed intake, and improve the growth of juvenile S. dumerili fed non-FM diets. Therefore, purified PL might be a good candidate to stimulate the growth of fish through enhancing the feed intake when they are fed diets containing alternative protein sources.     

A dietary energy level of 14.6 MJ kg−1 and protein-to-energy ratio of 20.2 g MJ−1 results in best growth performance and nutrient accretion in silver barb Puntius gonionotus fingerlings

Five iso-nitrogenous (300 g protein kg⁻¹ diet) and iso-lipidic (80 g kg⁻¹ diet) semi-purified experimental diets with variable energy levels of 10.5 (D-1), 12.5 (D-2), 14.6 (D-3), 16.7 (D-4) and 18.8 (D-5) MJ kg⁻¹ diets were fed to Puntius gonionotus fingerlings (average weight 1.79 ± 0.02 g) in triplicate groups (15 healthy fishes per replicate) for a period of 90 days to assess the optimum dietary energy level and protein-to-energy ratio (P/E). Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min⁻¹ were used for rearing the fish. Maximum specific growth rate, protein efficiency ratio, protein productive value, RNA : DNA ratio, whole body protein content, digestive enzyme activity and minimum feed conversion ratio was found in fish-fed diet D-3 with 14.6 MJ kg⁻¹ energy level. There were no improvements in all these parameters with the further rise in dietary energy level. Hence, it may be concluded that the optimum dietary gross energy level for maximum growth and nutrient utilization of silver barb is 14.6 MJ kg⁻¹ diet with a resultant P/E ratio of 20.2 g protein MJ⁻¹ diet, when the dietary protein and lipid are maintained at optimum requirement levels of 300 and 80 g kg⁻¹ diet, respectively, for this species.     

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50–1.50 g L⁻¹). Diets 1–6 were formulated to contain 360 g kg⁻¹ crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9–19.0 g kg⁻¹ dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.48±0.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg⁻¹ or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg⁻¹ dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg⁻¹ dry diet (37.8 g kg⁻¹ dietary protein).     

Effect of dietary pantothenic acid supplement on growth, body composition and intestinal enzyme activities of juvenile Jian carp (Cyprinus carpio var. Jian)

A 9-week feeding trial was carried out with juvenile Jian carp to study the effect of dietary pantothenic acid (PA) on growth, body composition and intestinal enzyme activities. Semi-purified diets with seven levels (4.0, 15.5, 25.6, 36.1, 45.9, 56.1 and 65.9 mg PA kg⁻¹) of supplemental calcium d -pantothenate were fed to Jian carp (13.0 ± 0.0 g). PA improved specific growth rate (SGR), protein productive value (PPV), protein efficiency ratio (PER) and lipid production value (LPV) ( P <  0.05). Fish fed the control diet had significantly lower feed efficiency (FE) than that in any other group ( P <  0.05). Body protein content increased with increasing PA levels ( P <  0.05), but moisture, lipid and ash of fish carcasses were negatively related to the graded PA levels ( P <  0.05). Intestine protein content (IPC), hepatopancreas protein content (HPC) and activity of α-amylase, lipase, trypsin, Na⁺,K⁺-ATPase, alkaline phosphatase (AKP) and gamma-glutamyl transpeptidase (γ-GT) were all positively affected by the dietary PA levels ( P <  0.05), while intestine index (ISI) and hepatopancreas index (HSI) decreased with the increment of supplemental levels of PA ( P <  0.05). These results suggested that PA could enhance fish growth and intestinal enzyme activities. The dietary PA requirement of juvenile Jian carp, Cyprinus carpio var . Jian (13.0–73.0 g), for optimal growth estimated by the broken-line analysis was 23.0 mg PA kg⁻¹ diet.     

Re-evaluation of total sulphur amino acid requirement and determination of replacement value of cystine for methionine in semi-purified diets of juvenile Nile tilapia, Oreochromis niloticus

Two feeding experiments were conducted to re-evaluate the total sulphur amino acid (TSAA; methionine and cystine) requirement and determine the replacement value of cystine for methionine of juvenile Nile tilapia ( Oreochromis niloticus ). Semi-purified diets used in both experiments contained 3510 kcal gross energy and 280 g of protein per kilogram diet from casein, gelatin and crystalline amino acids. The basal diet of the first experiment contained 3.1 g methionine and 0.4 g cystine per kilogram. l -methionine was added to the seven remaining diets at 1.0 g kg⁻¹ increment to produce methionine levels ranging from 3.1 to 10.1 g kg⁻¹ diet. Each diet was fed to four replicate groups of juvenile Nile tilapia (1.28 g mean weight) in a recirculation system for 8 weeks. Broken-line regression analysis of weight gain data indicated that the TSAA requirement of juvenile Nile tilapia was 8.5 g kg⁻¹ of the diet or 30.4 g kg⁻¹ of dietary protein. In the second experiment, TSAA level was set at 95% of the requirement value determined in the first experiment. Seven diets were made with different ratios of l -methionine and l -cystine (20 : 80, 30 : 70, 40 : 60, 50 : 50, 60 : 40, 70 : 30 and 80 : 20, based on an equimolar sulphur basis). Each diet was also fed to four replicate groups of juvenile Nile tilapia (4.14 g mean weight) in a recirculation system for 8 weeks. Regression analysis of weight gain data using broken-line model indicated that cystine (on a molar sulphur basis) could replace up to 49% of methionine requirement in semi-purified diets for juvenile Nile tilapia.     

Supplemental citric acid and particle size of fish bone-meal influence the availability of minerals in rainbow trout Oncorhynchus mykiss (Walbaum)

Juvenile rainbow trout Oncorhynchus mykiss (Walbaum) were fed six low-phosphorus (P) diets supplemented with two different sizes of ground fish bone-meals (fine, 68 μm or less; coarse, 250–425 μm) and a coarse bone-meal diet containing four levels of citric acid (0, 4, 8 or 16 g kg⁻¹ diet) to investigate the effects of pH and bone particle size on P bioavailability. The basal diet provided 3.4 g P   kg⁻¹ and bone-meal increased P contents to 5.4–6.0 g P   kg⁻¹. Coarse bone-meal diets supplemented with 0, 4, 8 or 16 g kg⁻¹ of citric acid had pH values of 6.0, 5.7, 5.4 and 5.0, respectively. Weight gain and whole-body water, protein and lipid contents were not influenced by bone-meal supplementation. Supplementing the basal diet with both coarse and fine bone-meal significantly increased whole-body ash content. Fish fed no bone-meal were hypophosphataemic compared with fish fed with either fine or coarse bone-meals. Phosphorus in fine bone-meal had higher availability than P in coarse bone-meal. Bone-meal supplementation significantly decreased whole-body manganese content from 8.9 μg g⁻¹ in fish fed no bone-meal to 2.3 and 4.5 μg g⁻¹ in fish fed with fine and coarse bone-meals, respectively. The concentration of magnesium increased but zinc concentration was not affected by bone-meal supplements. Citric acid increased whole-body ash content but the influence of citric acid on the body P content was not significant ( P  = 0.07). Dietary acidification by citric acid significantly increased whole-body iron in a linear fashion. The bioavailability of dietary P can be improved by fine grinding the bone in fish meals.