Dietary l‐lysine requirement of juvenile Chinese sucker,Myxocyprinus asiaticus

An 8‐week feeding trial was conducted to quantify the dietary l ‐lysine requirement of juvenile Chinese sucker with an initial weight of 1.81 ± 0.04 g reared in indoor flow‐through and aerated tanks. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of lysine (1.23%, 1.80%, 2.39%, 2.98%, 3.56% and 4.18% dry matter) at 0.6% increments from dietary ingredients and crystalline l ‐lysine. Each diet was randomly assigned to triplicate groups of 30 fish each and was fed to apparent satiation by hand three times a day (09:00, 13:00 and 17:00 hours) for 8 weeks. There were significant differences in growth performance and feed utilization among the treatments. Weight gain (WG), specific growth rate and protein efficiency ratio (PER) significantly increased with increasing lysine levels up to 2.39% of diet (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 when dietary lysine level increased from 2.39% to 4.18%. The N retention (% N intake) significantly increased with dietary lysine level but did not attain a plateau (P < 0.05). Survival could not be related to dietary treatments. Whole body protein increased (P < 0.05) and whole body lipid decreased (P < 0.05) with increasing dietary lysine level. The condition factor and hepatosomatic index were significantly affected by dietary lysine levels, however, viscersomatic index, whole body moisture and ash did not differ significantly among dietary treatments. Broken‐line analysis on the basis of WG and PER showed that dietary lysine requirements of juvenile Chinese sucker were 2.43% and 2.40% dry diet (5.52% and 5.45% dietary protein) respectively. Based on the ideal protein approach and the A/E ratios determined from muscle amino acid profile an estimation of the EAA requirements of Chinese sucker juveniles were calculated.     

Effects of dietary coated protease on growth performance,feed utilization,nutrient apparent digestibility,intestinal and hepatopancreas structure in juvenile Gibel carp (Carassius auratus gibelio)

This study was conducted to investigate the effects of dietary protease on growth performance, feed utilization, whole‐body proximate composition, nutrient digestibility, intestinal and hepatopancreas structure of juvenile Gibel carp, Carassius auratus gibelio (mean weight 8.08 ± 0.18 g). Six diets were prepared, including a positive control diet (dietary protein 350 g/kg, PC), one negative control diet (dietary protein 33 g/kg, NC) and four protease supplementations diets, which were 75, 150, 300 and 600 mg/kg protease NC diet. After 12 weeks of diet feeding in indoor recycle aquarium tanks, no significant difference (p > .05) was found on growth performance between fish fed diet with 75–600 mg/kg protease and the PC group. Compared with the fish fed the NC diet, the specific growth rate of fish fed 300 mg/kg protease increased significantly (p < .05), as well as protein efficiency ratios (p < .05), while feed conversion was the opposite (p < .05). The nutrient digestibility of crude protein and lipid was higher (p < .05) in fish fed 150 mg/kg protease diet than the PC diet. Whole‐body proximate composition of fish was not affected (p > .05) by the dietary treatment. Serum alkaline phosphatase and albumin were significantly affected by dietary protease (p < .05), while the content of total protein, glucose, triglyceride, total cholesterol, aspartate aminotransferase and alanine aminotransferase activities in serum was not affected (p > .05). Foregut muscular thickness was thinner (p < .05), when the fish fed diets supplementation of protease in 150 or 600 mg/kg diet than the NC diet. Protease activities in hepatopancreas and foregut were higher (p < .05), in the fish fed 150 or 300 mg/kg protease diet than the fish fed the PC diet, but those in the mid‐ and hindgut were not significantly affected (p > .05) by the dietary treatments. Based on the regression analysis of weight gain rate, the optimal dietary inclusion level of protease was 400 mg/kg in the diet for juvenile Carassius auratus gibelio.     

Effect of dietary carbohydrate level on growth performance,body composition,apparent digestibility coefficient and digestive enzyme activities of juvenile cobia,Rachycentron canadum L

A 9‐week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition and apparent digestibility coefficient and digestive enzyme activities of juvenile cobia. Six isonitrogenous and isolipidic diets containing graded levels of starch (1.3%, 6.5%, 12.5%, 18.4%, 24.2% and 30.4%) were fed to juvenile cobia. Specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary starch up to 18.4% (P<0.05), and thereafter SGR declined but FER and PER remained nearly the same. Apparent digestibility coefficient of starch reduced significantly when dietary starch up to 30.4%. Fish fed the diets with starch from 18.4% to 30.4% showed higher amylase activities in intestinal tract than those fed diets containing starch 1.3% and 6.5% (P<0.05). Significantly higher whole‐body lipid contents were observed in fish fed the diets containing higher starch. Whole‐body moisture content was inversely correlated with whole‐body lipid content, while protein and ash showed no significant differences. Plasma glucose, hepatosomatic index, liver glycogen and liver lipid increased with an increasing dietary starch. Based on SGR and FER, the appropriate dietary starch supplementations of juvenile cobia were estimated to be 21.1% and 18.0 % of diet respectively.     

Influence of dietary nucleotides supplementation on growth,body composition and fatty acid profile of Beluga sturgeon juveniles (Huso huso)

Effect of different levels (0%, 0.15%, 0.25%, 0.35% and 0.50%) of Optimûn, a commercial nucleotide (NT) product, on the growth performance, body composition and fatty acid profile of juvenile Beluga sturgeon (Huso huso) (12.57 ± 0.5 g) was investigated over a 62‐day period. This experiment was done in fifteen 600 L tanks, each stocked with 30 fish. Fish fed nucleotide showed significantly better growth performance (P < 0.05). Incorporation of 0.25% and 0.35% NT resulted in whole body protein content elevation, but the other proximate composition indices were not influenced by dietary nucleotide treatments. There were significant differences in saturated fatty acids (SFA) and total unsaturated fatty acids (TUFA) levels among fish fed on different experimental diets, while monounsaturated fatty acids, polyunsaturated fatty acids (PUFA), n‐3 PUFA, n‐6 PUFA, n3/n6 and eicosapentaenoic acid + docosahexaenoic acid were not influenced by NT. The results showed that diet supplementation with 0.35% Optimûn (NT) enhance growth performance, also administration of 0.25% and 0.35% affected chemical composition, as well as decreased SFA/TUFA ratio of Beluga juvenile.     

不同脂肪源对异育银鲫生长性能、机体成分、血清生化指标、体组织脂肪酸组成及脂质代谢的影响

试验以异育银鲫为研究对象,分别以日粮中添加5.4%鱼油、5.4%豆油、5.4%菜籽油、5.4%亚麻油为脂肪源,选择健康、规格、体质量基本一致的异育银鲫336尾,随机分为4组,每组3个重复、在可控温循环流水圆形蓄养槽内进行为期64 d的投喂试验,探讨不同脂肪源对异育银鲫生长、体成分及血清生化指标的影响。试验结果表明:豆油组及菜籽油组增重率、特定生长率显著高于鱼油组,豆油组肥满度显著低于鱼油组及亚麻油组,各试验组末均体质量、饲料系数、肝体比及脏体比均没有显著差异(P>0.05);各组间肌肉水分、粗脂肪、粗蛋白及粗灰分均无显著差异(P>0.05);不同饲料脂肪源对鱼体肌肉脂肪酸组成有显著影响,并且鱼体脂肪酸的组成与饲料脂肪酸的组成有很大相关性,其中鱼油组与菜籽油组有极显著相关性(P<0.01),豆油组显著相关(P<0.05);鱼油组的血清谷丙转氨酶、谷草转氨酶及碱性磷酸酶活性显著高于其它组(P<0.05);各试验组间胰岛素、皮质醇、总蛋白、白蛋白、球蛋白、白球比、血糖、胆固醇及甘油三酯均无显著差异(P>0.05);各组肉碱软脂酰基转移酶-Ⅰ(CPT-Ⅰ)、肉碱软脂酰基转移酶-Ⅱ(CPT-Ⅱ)、脂肪酶、乙酰辅酶A羧化酶(ACC)及脂蛋白脂酶(LPL)均无显著差异(P>0.05)。因此,日粮中添加一定量的豆油、菜籽油或亚麻油同样能取得良好的生长效果,为以后生产中以菜籽油或亚麻油替代豆油或鱼油提供了理论依据,节约了生产成本。     

Effects of fish meal replacement with animal protein blend on growth performance,nutrient digestibility and body composition of juvenile Chinese soft‐shelled turtle Pelodiscus sinensis

An 8‐week feeding trial was conducted to evaluate the potential of partial replacement of fish meal with rendered animal protein blend (APB) [meat and bone meal (MBM): expanding blood meal (EBM) = 4 : 1] in the diet of juvenile Chinese soft‐shelled turtle Pelodiscus sinensis. Seven isonitrogenous and isoenergetic practical diets replacing 0%, 10%, 20%, 30%, 40%, 50% and 60% fish meal protein by APB were formulated. Weight gain, feed efficiency, protein efficiency and the apparent digestibility coefficients (ADCs) of dry matter and gross energy in the experimental diets all exhibited no significant difference (P > 0.05) when dietary fish meal was replaced for 0–40%, but decreased significantly (P < 0.05) with further increasing substitution levels. However, relative feed intake, ADC of lipid as well as the contents of whole‐body moisture, protein, lipid and ash all showed little differences (P > 0.05) among all the treatments. Nitrogen retention and the ADCs of protein and most amino acids all decreased significantly (P < 0.05) when fish meal was substituted by more than 30%. The results indicated that fish meal in the practical diet of juvenile Chinese soft‐shelled turtle could be replaced by 30–40% using a combination of MBM and EBM without negative effects on growth performance, nutrients digestibility and body composition.     

Dietary arginine requirement of juvenile cobia ( Rachycentron canadum)

A 9‐week feeding trial was conducted to estimate the dietary requirement of arginine in juvenile cobia in indoor flow‐through and aerated aquaria. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of arginine ranging from 1.76% to 3.75% (dry weight) at about 0.4% increments replaced by equal proportions of glycine. Survival was not significantly different among dietary treatments. Specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary arginine up to the 2.96% diet (P < 0.05), and thereafter declined. The whole body crude protein content was significantly affected by dietary arginine (P < 0.05), while moisture, crude lipid and ash showed no significant differences among dietary treatments. The essential amino acid contents of muscle were not significantly affected by dietary arginine. The serum nitric oxide synthase activities in fish fed diets with arginine from 2.18% to 3.75% were significantly higher than activities in fish fed the diet with 1.76% arginine (P < 0.05). On the basis of SGR and FER, the optimal dietary arginine requirements of juvenile cobia were estimated to be 2.85% of the diet (6.20% of dietary protein) and 2.82% of the diet (6.13% of dietary protein), respectively, using second‐order polynomial regression analysis.     

Effects of total replacement of fish oil by pork lard or rapeseed oil and recovery by a fish oil finishing diet on growth,health and fish quality of gibel carp (Carassius auratus gibelio)

An 84‐day growth trial was designed to investigate effects of dietary replacements fish oil with pork lard (PL) or rapeseed oil (RO) on growth and quality of gibel carp (Carassius auratus gibelio var. CAS III) (initial body weight: 158.2 ± 0.2 g), and responses of the fish refed fish oil (FO) diet. Three isonitrogenous (crude protein: 30%) and isolipid (crude lipid: 10%) diets were formulated containing 7.73% FO, PL or RO. Five experimental treatments including FO group (FO), PL group (PL), RO group (RO), group fed PL for 42 days and refed FO for 42 days (PL+rFO), RO and refed FO group (RO+rFO) was tested. At the end of first 42 days, the fish fed PL and RO had higher mortality than that of the control (P > 0.05). At the end of whole experiment, fish fed PL and RO showed higher plasma cortisol than FO fish (P < 0.05). RO+rFO fish showed higher lysozyme activity than RO fish (P < 0.05). Fish growth and feed utilization, composition of whole body and muscle, free amino acids, texture, off‐flavour substances or sensory attributes were not affected by dietary treatments (P > 0.05). PL and RO diet decreased muscle EPA, DHA and n‐3/n‐6 ratio (P < 0.05), while FO‐refeeding had recovery effect. It can be concluded that the replacement of FO by PL and RO does not affect the growth, feed utilization or fish tasting quality in gibel carp. Fish muscle fatty acids modified by dietary PL and RO can be recovered by refeeding with FO diet.     

Effects of replacement of dietary fish oil with soybean oil on growth performance and tissue fatty acid composition in marine herbivorous teleost Siganus canaliculatus

Fish oil (FO) substitution has been studied in many marine carnivorous fish, but seldom in marine herbivorous or omnivorous species. To evaluate the feasibility of using soybean oil (SO) as a dietary lipid and confirm its capability of converting C₁₈ polyunsaturated fatty acid (PUFA) into long chain polyunsaturated fatty acid (LC‐PUFA) in the marine herbivorous teleost Siganus canaliculatus, juvenile fish were fed with four formulated diets differing in lipid composition, with SO accounting for 0.76% (SO0), 23% (SO23), 45% (SO45) and 67% (SO67) of total dietary lipid respectively. After feeding for 8 weeks, growth performance including weight gain, specific growth rate, feed conversion ratio and protein efficiency rate were better in the SO23 and, especially, SO45 groups than in the SO0 and SO67 groups (P < 0.05). Tissue fatty acid compositions were affected by diet, with the liver contents of eicosapentaenoic (EPA), docosapentaenoic (DPA), docosahexaenoic (DHA) acids and total n‐3 PUFA displaying parallel changes with the corresponding dietary fatty acids. While the muscle contents of EPA, DPA and total n‐3 PUFA between SO0 and SO23 groups, and the liver contents of arachidonic acid (ARA) and 20:4n‐3, as well as the muscle content of 20:3n‐6 between SO0 and SO45 groups showed no difference, confirming the biosynthesis of LC‐PUFA from C₁₈ precursors in vivo as the contents of corresponding fatty acids in diets SO23/SO45 were much lower than those in diet SO0 (P < 0.05). The results indicate that SO may be a suitable dietary lipid source for S. canaliculatus, and can replace up to 67% or 45% of total dietary FO without negatively compromising growth performance or nutritional quality of fish respectively. Moreover, the study increases our knowledge of FO substitution in marine herbivorous fish.     

Effects of dietary carbohydrate/lipid ratios on growth performance,body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58.     

Dietary lipid requirements of larval genetically improved farmed tilapia,Oreochromis niloticus (L.), and effects on growth performance,expression of digestive enzyme genes,and immune response

The present study was performed to investigate the effects of dietary lipid level on growth performance, antioxidant defense, and mRNA levels of digestive enzymes and immune genes in larval genetically improved farmed tilapia (Oreochromis niloticus). The results show that larvae fed lipid levels of 4–11.5% had greater weight gain (WG), feed efficiency, protein efficiency ratio and survival than larvae fed the other dietary lipid levels (P < 0.05). No difference whole‐body crude protein, ash or moisture contents were found between treatments (P > 0.05) but lipid contents increased as dietary lipid level was increased. The 8% and 11.5% dietary lipid levels had stimulatory effects on trypsin mRNA level compared with those of larvae fed the 15% and 18.5% lipid diets. Intestinal and liver amylase mRNA levels decreased in larvae fed the 18.5% lipid diet, following the decrease in dietary starch. Analysis of the secondary curve equation for WG indicated that the optimal dietary lipid level in larval tilapia was 8.56%. In addition, the 4–11.5% lipid levels improved superoxide dismutase and glutathione peroxidase activities and increased mRNA levels of heat shock protein70, hepcidin antimicrobial peptide‐1, and C‐type lysozyme in the liver of larvae (P < 0.05). A 192‐h Streptococcus iniae challenge study was conducted after the 35‐day feeding trial, and the results showed that post‐challenge mortality of larvae fed the 11.5% lipid level was the lowest and enhanced the immune activities.     

Effects of dietary 60 g kg−1 dried distiller's grains in least‐cost practical diets on production and gut allochthonous bacterial composition of cage‐cultured fish: comparison among fish species with different natural food habits

Dried distiller's grain (DDG) is considered as an alternative ingredient of dietary feed due to its high contents of protein, fibre and fat. In this study, 60 g kg^‐1 of DDG was used to feed grass carp (Ctenopharyngodon idella), bluntnose black bream (Megalobrama amblycephala), gibel carp (Carassius gibelio) and black carp (Mylopharyngodon piceus) for 8 weeks, and its effect on fish production and gut allochthonous microbiota was investigated for the development of a suitable fish feed high in nutrients and low in cost for polyculture freshwater fish. DDG supplementation resulted in the less weight gain and higher feed conversion ratio of black carp (P < 0.05), but had no significant effects on other fish or parameters. PCR–denaturing gradient gel electrophoresis (DGGE) analysis indicated that all four fish species had some common and unique bacteria in their digestive tracts, and the gut microbiota of bluntnose black and gibel carp fed the control diet and DDG diets were very similar (Cs > 91%); of them, the total counts of intestinal bacteria studied by qPCR increased in grass carp (P < 0.05) and depressed in black carp (P < 0.05) when fed dietary DDG. Thus, we assumed that dietary DDG modulated production and gut microbiota of fish in a host‐specific way.     

Growth,body chemical composition and trypsin activity of South American catfish,surubim (Pseudoplatystoma sp.) juveniles fed different dietary protein and lipid levels

To evaluate protein and lipid requirement of South American catfish surubim (Pseudoplatystoma sp.) juveniles, nine semi‐purified diets containing three levels of protein (40%, 45% and 50%) and three levels of lipid (12%, 16% and 20%) were tested. After 8‐week feeding trial, body weight increase averaged 2124.3 ± 295.7%. Growth performance was significantly affected by dietary level of protein (P < 0.05). At the 40% protein level, increasing level of dietary lipid had a positive effect on final individual mean weight (protein sparing effect). Whole body protein and moisture contents were affected by the dietary level of lipid (P < 0.05). Whole body lipid content positively correlated with the level of dietary lipid (P < 0.05). Cannibalism related mortality was observed despite rearing fish in 24 h dark. Fatty acid composition of fish was affected by the dietary lipid level (P < 0.05). Polyunsaturated fatty acids increased with the increasing level of dietary lipid while saturated fatty acids and monounsaturated fatty acids decreased. Trypsin activity in the digestive tract of surubim was influenced by dietary levels of protein and lipid (P < 0.05). Our preliminary results suggest that the optimum protein/lipid ratio might be close to 45/16% for surubim juveniles.     

Dietary total phosphorus requirement of juvenile yellow catfish <Emphasis Type="Italic">Pelteobagrus fulvidraco</Emphasis>

The present experiment was conducted to determine the dietary total phosphorus requirement of juvenile yellow catfish Pelteobagrus fulvidraco. Six diets with increasing dietary phosphorus concentration (0.43, 0.55, 0.78, 0.90, 1.05 and 1.18% of dry matter, respectively) were fed to triplicate groups of 20 fish each (mean initial body weight, 2.68 ± 0.08 g, mean ± SD) to apparent satiation for 7 weeks. Weight gain and specific growth rate (SGR) increased with increasing dietary phosphorus level from 0.43 to 0.90% and then declined over dietary phosphorus level of 0.90% (P < 0.05). Phosphorus retention increased with increasing dietary phosphorus level from 0.43 to 0.55% and then declined over dietary phosphorus level of 0.55% (P < 0.05). Dietary phosphorus levels significantly influenced whole body crude protein and ash contents (P < 0.05), but not whole body lipid content (P > 0.05). Vertebrae phosphorus content increased with dietary phosphorus level from 0.43 to 0.78% (P < 0.05) and then plateau over the level of 0.78% (P > 0.05). Dietary phosphorus level significantly influenced condition factor, viscerosomatic index and hepatosomatic index (P < 0.05). The relationship between SGR and whole body ash content against dietary phosphorus levels could be expressed as a second-order polynomial equation and the points of 0.89 and 0.85% were considered to be the optimal dietary total phosphorus level, respectively. Based on broken-line analysis of vertebrae phosphorus content, the minimal dietary total phosphorus requirements for maintaining maximum phosphorus storages were estimated to be 0.76% phosphorus.     

Effects of dietary macronutrient level and feeding frequency on growth and body composition of juvenile rockfish (Sebastes schlegeli)

An 8-week feeding experiment was conducted to investigate the effects of different dietary macronutrient level and feeding frequency on the growth, feed utilization, and body composition of juvenile rockfish. Triplicate groups of fish (body weight of 4.1 g) were fed the experimental diets containing either high levels of carbohydrate (HC, 35%), lipid (HL, 13%), or protein (HP, 55%) at different feeding frequencies (twice daily, once daily, and once every 2 days). Weight gain was affected by feeding frequency but not by dietary composition. Weight gain of fish fed the diets once every 2 days was significantly (P < 0.05) lower than that of other groups. Daily feed intake and energy intake were affected by both dietary composition and feeding frequency. Daily feed intake of fish fed the HC diet was significantly (P < 0.05) higher than that of fish fed the HL and HP diets at the same feeding frequency. Feed efficiency and protein efficiency ratio were affected by both dietary composition and feeding frequency and decreased with increasing feeding frequency in the same dietary composition. Feed efficiency and protein efficiency ratio of fish fed the HC diet were significantly (P < 0.05) lower than those of fish fed the HL diet at the same feeding frequency. Whole-body lipid content of fish fed the HL diet was significantly (P < 0.05) higher than that of fish fed the HC and HP diets at the same feeding frequency. These results indicate that an increase of dietary lipid level compared with dietary carbohydrate level may have the advantage of a protein-sparing effect at same feeding frequency, and a once-daily feeding regime is more effective than twice daily or one feeding every 2 days to improve growth performance of juvenile rockfish grown from 4 to 21 g.     

Effects of varying dietary docosahexaenoic acid levels on growth,proximate composition and tissue fatty acid profile of juvenile silver pomfrets,Pampus argenteus (Euphrasen, 1788)

This study investigated the effects of varying dietary levels of decosahexaenoic acid (DHA) on growth performance, proximate composition and whole body fatty acid profiles of juvenile silver pomfret, Pampus argenteus. Triplicate groups of fish (30.55 ± 0.08 g) were fed diets containing 5.2%, 9.31% and 13.38% DHA (% of total fatty acids) or 0.85%, 1.52% and 2.18% DHA on dry diet weight for diets 1, 2 and 3 respectively. Survival was not affected by dietary DHA levels. The growth performance and feed utilization parameters of fish fed diets 2 and 3 were significantly (P < 0.05) higher than those fed diet 1, although these parameters in diets 2 and 3 did not differ significantly (P > 0.05). Whole body lipid and fatty acid profiles were influenced by dietary DHA levels. Significantly higher n‐3 fatty acids particularly DHA, DHA:EPA(eicosapentaenoic acid) ratios and n‐3:n‐6 ratios were observed in fish fed diets 2 and 3 compared to those fed diet 1. Better growth performance and higher whole body DHA:EPA (2.31, 2.29) ratios and n‐3:n‐6 ratios (2.17, 2.12) observed in fish fed diets 2 and 3, respectively, suggests that silver pomfret juveniles have a higher requirement for n‐3 fatty acids, notably DHA for optimum growth and survival.     

Effect of dietary phytic acid and semi‐purified lignin on energy storage indices,growth performance,nutrient and energy partitioning of rainbow trout,Oncorhynchus mykiss

The effect of dietary phytic acid (PA) and semi‐purified lignin, and their interactions on growth performance, energy storage indices, nutrient deposition and partitioning in rainbow trout were studied in a 12‐week growth trial. Six isoproteic and isoenergetic diets were formulated differing only in their PA and lignin concentrations. In these diets, five essential amino acids: histidine, lysine, methionine (+ cysteine), threonine and tryptophan were formulated to be marginally adequate to the dietary requirement. Fish were pair‐fed with the amount of feed adjusted on a weekly basis. Among the performance indicators, dietary PA levels affected only the Fulton's body condition index (FCI) and whole carcass nitrogen retention efficiency (NRE; P < 0.05). On the contrary, lignin did not affect the whole carcass protein deposition (PD) and NRE but the lipid deposition (LD; P < 0.05), lipid retention efficiency (LRE; P < 0.01) and PD‐LD ratio (P < 0.05). Neither lignin nor phytic acid affected any parameters in dressed carcass and in viscera of rainbow trout except the visceral LD, which was affected only by the PA‐lignin interactions (P < 0.05).     

Optimal dietary carbohydrate‐to‐lipid ratios for silvery‐black porgy (Sparidentex hasta) juveniles

Four isonitrogenous diets containing different carbohydrate:lipid (CHO:L) ratios (0.3, 0.6, 1.1 and 1.8) were tested in triplicate groups (16 fish per replicate) of silvery‐black porgy juveniles for 8 weeks. Growth performance was not affected by different dietary CHO:L ratios (P > 0.05); however, the viscerosomatic index, the intraperitoneal fat, whole‐body lipid, energy and n‐3 long chain polyunsaturated fatty acids levels increased with decreasing dietary CHO:L ratios (P < 0.05). Fish fed with 1.8 CHO:L diet had the lowest apparent digestibility coefficients of protein and lipid, as well as the lowest plasma haemolytic and lysozyme activities (P < 0.05). Red blood cell counts and plasma glucose levels were higher in fish fed with 1.1 and 1.8 CHO:L ratio diets than in the other groups (P < 0.05). Plasma alkaline phosphatase and alanine aminotransferase, as well as the level of lipid peroxidation and total antioxidant capacity in the liver and plasma increased as dietary CHO:L ratios decreased (P < 0.05). The results of the current study indicated that the diets with CHO:L ratios between 0.6 and 1.1 are optimal for silvery‐black porgy, whereas higher ratios may result in hyperglycaemia and immune suppression, and lower CHO:L ratios may lead to oxidative stress and liver dysfunction.     

Effects of different dietary lipid sources on tissue fatty acid composition,serum biochemical parameters and fatty acid synthase of juvenile mud crab Scylla paramamosain (Estampador 1949)

A 6‐week study was conducted to determine the effects of different lipid sources in pelleted diets on juvenile mud crab Scylla paramamosain. Five isonitrogenous and isolipidic diets containing 8% level of fish oil (FO), lard (LD), safflower oil (SO), perilla seed oil (PO) or mixture oil (MO; V_FO:V_SO:V_PO = 1:1:1), and a live food of marine bivalve Potamocorbula rubromuscula as the control diet (CF), were fed to groups of 25 juvenile crabs (average initial weight 7.4 g, carapace width 3.5 cm) in triplicate. The results showed that crabs fed MO had the highest survival (P < 0.05). The moisture content was significantly higher in crabs fed LD, SO and PO (P < 0.05). Crabs fed SO exhibited the lowest crude protein and lipid (P < 0.05). Ash contents were obviously lower in LD group (P < 0.05). Highest total lipid in the hepatopancreas and muscle was in LD and FO group respectively. Glucose, total cholesterol and low‐density lipoprotein were higher while high‐density lipoprotein was lower (P < 0.05) in LD group. Tissue fatty acid compositions were consistent with those in diets. FO and MO diets had the same depression effect like CF on fatty acid synthase activity and mRNA expression in the hepatopancreas. The results of this study indicated that FO and mixed oil are suitable for preparation of pelleted diets with better effects for juvenile S. paramamosain compared with live food, and the ratio of n‐6/n‐3 fatty acids in pelleted diets must be <1.