Effects of dietary n‐3HUFA on different growth stages of the white shrimp,Litopenaeus vannamei: Growth,haematological characteristics,enzyme activities and fatty acid profiles

This study investigated the effects of n‐3 high unsaturated fatty acid (n‐3HUFA) levels on the growth performance, antioxidant enzyme activities and fatty acid profiles of both subadult and adult Litopenaeus vannamei (L. vannamei). Seven iso‐nitrogenous and iso‐lipidic diets were used, containing n‐3HUFA concentrations of 1.6 (control), 4.8, 7.4, 13.9, 23.9, 29.2 and 34.4 g/kg, respectively. Two 8‐week feeding trials were conducted to determine the dietary n‐3HUFA requirements of L. vannamei with an initial body weight of 4.25 ± 0.00 g (subadults) and 8.50 ± 0.01 g (adults). The results showed that the dietary n‐3HUFA level significantly affected the weight gain rate (WGR), specific growth rate, the feed conversion ratio and the hepatosomatic index (HSI) (p < 0.05), but did not significantly affect the survival rate (p > 0.05). At appropriate level, dietary n‐3HUFA improved growth performance and HSI of both subadult and adult L. vannamei. Both subadults and adults showed significant differences in body composition (p < 0.05), except for moisture and crude ash (p > 0.05). Cholesterol and low‐density lipoprotein significantly decreased with increasing dietary n‐3HUFA both in subadults and adults (p < 0.05); however, triglyceride showed no significant change (p > 0.05). High‐density lipoprotein (HDL) in subadults was significantly affected by dietary n‐3HUFA (p < 0.05), but followed no apparent regularity; HDL significantly changed in adults and showed an upward trend followed by a downward trend (p < 0.05). There was no significant effect on aspartate transaminase (AST) activity in subadults, but AST in adults and alanine transaminase (ALT) in subadults and adults were significantly affected (p < 0.05). Dietary n‐3HUFA significantly affected serum polyphend oxidase, malic dehydrogenase, alkaline phosphatase, superoxide dismutase and sodium‐potassium adenosine triphosphatase enzyme activities in gills (p < 0.05). The fatty acid composition of the shrimp tissue was associated with the fatty acid composition of the diet. Dietary n‐3HUFA supplementation significantly improved the contents of tissue ∑HUFA and n‐3HUFA, increased the n‐3/n‐6 ratio in the tail muscle and decreased the contents of tissue polyunsaturated fatty acid and saturated fatty acid (p < 0.05). Based on the WGR, the broken‐line equations indicated that the optimum requirements of dietary n‐3HUFA were determined to be 9.0 and 5.1 g/kg for subadult and adult L. vannamei, respectively.     

Effect of the dietary phosphatidylcholine at different growth stages of Pacific white shrimps,Litopenaeus vannamei

This study investigated the effects of dietary phosphatidylcholine (PC) at different growth stages of Litopenaeus vannamei (L. vannamei) with an initial weight of 0.70 ± 0.00 g (juvenile) and 4.25 ± 0.00 g (subadult) for 8 weeks. Six isonitrogenous and isoenergetic diets containing PC (0, 1.7, 5.1, 6.8, 10.2 and 13.6 g/kg) were confected using formulated with redfish meal, dehulled soybean meal and peanut meal as protein source, fish oil and corn oil as fat source. The juveniles were reared in 0.3 m³ aquarium at the density of 40 in triplicates, as well as the subadults in 0.5 m³ at the density of 40 in triplicates. Results showed PC level had significant effects on weight gain rate (WGR), specific growth rate, feed conversion ratio in juvenile and subadult shrimps and hepatosomatic index in juvenile shrimps (p < 0.05). No significant differences were found in moisture, whole body protein and crude ash (p > 0.05). Crude fat of juveniles had no significant change (p > 0.05), but subadults increased significantly (p < 0.05). Both juveniles and subadults showed that triglyceride and low‐density lipoprotein presented a downward trend with PC elevating, but high‐density lipoprotein increased gradually. Cholesterol in juveniles presented upward, but downward in subadults (p < 0.05). Dietary PC also significantly reduced the aspartate transaminase in juveniles and alanine transaminase in subadults (p < 0.05). PC supplementation significantly improved the glutathione S‐transferase activity and reduced the content of malondialdehyde in the hepatopancreas (p < 0.05). PC supplementation significantly improved gill filament sodium‐potassium adenosine triphosphatase enzyme of juvenile shrimps (p < 0.05), but subadult shrimps were not influenced (p > 0.05). PC supplementation significantly elevated the content of hepatopancreas eicosapentaenoic acid, highly unsaturated fatty acid (HUFA) and n‐3HUFA (p < 0.05), but the content of linoleic acid significantly reduced (p < 0.05). The broken‐line and quadratic regression model based on WGR showed the optimum dietary PC requirement was 10.3 g/kg and 6.5 g/kg for juveniles and subadults, respectively.     

Effects of phospholipid addition to diets with different inclusion levels of fish oil on growth and fatty acid body composition of juvenile swimming crab Portunus trituberculatus

Six experimental diets were designed with two phospholipid (PL; 0% and 1.5%) and three fish oil levels (0%, 1% and 3%) to evaluate the effects of dietary fish oil and PL levels on growth, survival and fatty acid composition of juvenile swimming crab, Portunus trituberculatus. Diets were iso‐energetic and iso‐nitrogenous and each diet was fed to triplicate groups (initially weight, 24.88 ± 0.04 g per crab) for 59 days. Weight gain (WG) and specific growth rate (SGR) increased with dietary PL addition to 0% fish oil‐supplemented diets (P < 0.05). On the other hand, WG and SGR decreased with dietary PL addition to 3% fish oil diets (P < 0.05). Crabs fed PL supplemented diets had higher haemolymph low‐density lipoprotein cholesterol concentrations and muscle crude lipid levels (P < 0.05) than crabs fed a none PL supplemented diet. The percentage of highly unsaturated fatty acids (HUFA; % total FA) in both polar and neutral lipids fractions of muscle tissue only increased in case of PL addition to 0% and 1% fish oil‐supplemented diets (P < 0.05). HUFA levels in the neutral lipids fraction of the hepatopancreas increased by dietary PL addition at each dietary fish oil level (P < 0.05). In this study, both dietary fish oil and PL addition contributed to a high n‐3/n‐6 ratio in muscle and hepatopancreas of P. trituberculatus. In conclusion, PL addition is only meaningful with fish oil‐deficient diets, in which case it enhanced lipid transport and HUFA absorption efficiency, hence improving the nutritional value of the diet.     

Schizochytrium as a replacement for fish oil in a fishmeal free diet for jade perch,Scortum barcoo (McCulloch & Waite)

A 10‐week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso‐nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n‐3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n‐3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n‐3 HUFA and n‐6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n‐3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n‐3 HUFA content towards the same concentration of n‐3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.     

Effect of Dietary n‐3 highly unsaturated fatty acids on Growth,Body Composition and Fatty Acid Profiles of Juvenile Black Seabream,Acanthopagrus schlegeli (Bleeker)

An 8‐wk feeding trial was conducted to investigate the effects of dietary n‐3 highly unsaturated fatty acids (n‐3 HUFA) on growth, body composition, and fatty acid profiles of juvenile Acanthopagrus schlegeli. Three replicate groups of fish (initial mean weight: 8.08 ± 0.09 g, mean ± SD) were fed diets with different levels of n‐3 HUFA (0.76%, HUFA_0.76; 0.83%, HUFA_0.83; 0.90%, HUFA_0.90; 0.97%, HUFA_0.97; 1.04%, HUFA_1.04; 1.12%, HUFA_1.12) at 12.9% of total lipid, with a constant eicosapentaenoic acid (EPA, 20:5n‐3) to docosahexaenoic acid (DHA, 22:6n‐3) ratio of about 2.1. Hepatosomatic index (HSI) and intraperitoneal fat (IPF) ratio were all linearly depressed by dietary n‐3 HUFA levels (P < 0.05), and condition factor (CF) was not affected. Adipocyte diameter in IPF decreased with the elevation of dietary n‐3 HUFA and significance occurred between group HUFA_0.90 and HUFA_1.12. Lipid content in dorsal muscle was significantly lowered by dietary n‐3 HUFA compared to fish fed diet HUFA_0.76. No significance was found in whole fish proximate composition. In liver, dorsal muscle and IPF, ∑SFA, 16:0 or ∑n‐3 HUFA were all positively correlated with dietary n‐3 HUFA, while DHA to EPA ratios remained constant in 2.68, 2.86, and 3.60, respectively. Fatty acid synthase (FAS, EC 2.3.1.85) activities of all treatments remained constant at first and then were significantly elevated by dietary n‐3 HUFA higher than 0.97% (P < 0.05). In contrast, hormone sensitive lipase (HSL, EC 3.1.1.3) changed following an opposite tendency. Quadratic analysis based on weight gain rate (WGR) indicated that dietary n‐3 HUFA requirement for juvenile black seabream was 0.94% of the diet in 12.9% lipid diets .     

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei: II. Effect of dietary n-3 and n-6 polyunsaturated and highly unsaturated fatty acids on juvenile shrimp growth, survival, and fatty acid composition

This study evaluated the nutritional value of dietary n‐3 and n‐6 polyunsaturated fatty acids (PUFA) such as linoleic (LOA) and linolenic (LNA) acids, and highly unsaturated fatty acids (HUFA) such as arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids for juvenile Litopenaeus vannamei, based on their effects on growth, survival, and fatty acid composition of hepatopancreas and muscle tissue. Diets contained 5% total lipid. A basal diet contained palmitic and stearic acids each at 2.5% of diet. Five diets contained 0.5% dry weight of LOA, LNA, AA, EPA, or DHA. An additional diet evaluated HUFA in combination by supplementing at 0.5% of diet, a mixture of n‐3 HUFA. All HUFA showed higher nutritional value than PUFA for shrimp and produced significantly (P < 0.05) higher final weight, weight gain, and total lipid in shrimp muscle. Fatty acid profiles of shrimp tissues reflected the composition of the dietary lipids. In general, saturated fatty acids were more abundant in the neutral factions, while PUFA and HUFA were more abundant in the polar fractions of tissues. Under these experimental conditions, HUFA had much greater nutritional value than PUFA for juvenile L. vannamei; moreover, dietary requirements for PUFA were not demonstrated.     

Effects of different levels of dietary protein on the growth performance,nutrient utilization,digestive enzymes and physiological status of white shrimp,Litopenaeus vannamei juveniles reared in inland saline water

A 60‐day feeding trial was conducted to illustrate the effect of dietary protein levels on the growth and physio‐metabolic responses of juvenile Litopenaeus vannamei reared in inland saline water (ISW). Six isoenergetic (15 MJ/kg) and isolipidic (60 g/kg) diets with graded level of crude protein viz., 240 (T240), 260 (T260), 280 (T280), 300 (T300), 320 (T320) and 340 (T340) g/kg diet were formulated. Significantly higher (p < .05) weight gain (%), specific growth rate, with lower food conversion ratio were found in T320 and T340 groups. The protein utilizing efficiency and whole‐body protein content were significantly higher (p < .05) in the T320 group. Trypsin activity increased with the increasing dietary CP level but amylase activity decreased with the increasing dietary CP level. Transaminase enzymes, haemolymph protein and haemocyanin were elevated in T320 and T340 groups. The lactate dehydrogenase and malate dehydrogenase activities were significantly higher (p < .05) in the T240 group. Shrimp of T240 group had the lowest (p < .05) glycogen and total haemocyte count with highest (p < .05) haemolymph glucose and antioxidant enzymes activities than the other groups. Based on the results, feeding 320 g CP/kg is found to be optimum for supporting maximum growth and health status of L. vannamei reared in ISW at 8 g/L salinity. The finding of the present study will help in developing a low‐cost feed for L. vannamei reared in ISW.     

Effects of dietary phospholipids and highly unsaturated fatty acids on the precocity,survival, growth and hepatic lipid composition of juvenile Chinese mitten crab,Eriocheir sinensis (H. Milne‐Edwards)

Precocious puberty is one of the major constraints to the further development of Chinese mitten crab (Eriocheir sinensis) farming industry. Although dietary phospholipids (PL) and highly unsaturated fatty acids (HUFA) supplementation have been shown to enhance the growth of larval E. sinensis in other studies, it is still unknown whether this also leads to a higher precocity rate for juvenile E. sinensis. This study was conducted to investigate the effects of dietary PL and HUFA on precocity, survival, growth and hepatic lipid composition of juvenile E. sinensis. Two diets were formulated with PL [3.95% dry weight (DW)] and HUFA (0.98% DW) supplementation (diet A) and without PL and HUFA supplementation (diet B) and fed to juvenile E. sinensis. Although dietary PL and HUFA levels did not significantly affect the survival and growth performance of juvenile E. sinensis, compared with crabs fed diet A, a higher precocity rate was found among juvenile E. sinensis fed diet B (P=0.051). A higher total lipid content, but significantly lower levels of HUFA and PL (P<0.05) were found in the hepatopancreas of crabs fed diet B than in those fed diet A. Meanwhile, the precocious females had significantly lower hepatosomatic index, arachidonic acid (20:4n‐6), eicosapentaenoic acid (20:5n‐3) and docosahexaenoic acid (22:6n‐3) contents in their hepatopancreas when compared with that of the normal immature juveniles (P<0.05). The results suggest that the occurrence of precocious puberty among farmed juvenile E. sinensis could be reduced by the inclusion of appropriate level of dietary PL and HUFA.     

Dietary n‐3 highly unsaturated fatty acids affect the biological and serum biochemical parameters,tissue fatty acid profile,antioxidation status and expression of lipid‐metabolism‐related genes in grass carp,Ctenopharyngodon idellus

A 95‐day feeding trial was conducted to determine the effects of n‐3 highly unsaturated fatty acids (n‐3 HUFA) on the growth, antioxidation and lipid metabolism in grass carp (Ctenopharyngodon idellus). Two isonitrogenous and isolipidic diets were formulated with either lard oil (LO) or fish oil (FO) as the main lipid source. The results showed that the intraperitoneal fat (IPF) ratio was significantly lower (P < 0.05) in FO group. The concentration of n‐3 HUFA in muscle, hepatopancreas and IPF was significantly higher in FO group (P < 0.05). The serum low‐density lipoprotein (LDL) content was significantly lower (P < 0.05), and glucose (GLU) content was significantly higher (P < 0.05) in FO group. The serum total superoxide dismutase (T‐SOD) activity was significantly higher (P < 0.05) in FO group, consistent with the serum malondialdehyde (MDA) content. The gene expression of IPF fatty acid synthase (FAS), acetyl‐CoA carboxylase (ACC), sterol regulatory element‐binding protein (SREBP‐1) and peroxisome proliferator‐activated receptor γ (PPARγ) was significantly lower (P < 0.05) and that of peroxisome proliferator‐activated receptor α (PPARα) was significantly higher (P < 0.05) in FO group compared with LO group. Similar trends were found in the hepatopancreas, except for PPARγ. It is suggested that n‐3 HUFA could inhibit lipid accumulation in grass carp by affecting the expression of lipid‐metabolism‐related genes.     

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei: I. Effect of dietary linoleic and linolenic acids at different concentrations and ratios on juvenile shrimp growth, survival and fatty acid composition

A 6‐week feeding trial was conducted to evaluate the nutritional value of dietary linoleic (18:2n‐6, LOA) and linolenic (18:3n‐3, LNA) acids for juvenile Litopenaeus vannamei by determining their effects on growth, survival and fatty acid composition of hepatopancreas and muscle tissue. Diets were formulated to contain 5% total lipid. A basal diet contained only palmitic and stearic acids, each at 2.5% of diet. Six diets contained one of three levels (0.25, 0.5 and 1%) of either LOA or LNA, and three diets had different ratios of LNA/LOA (1, 3, 9) at a combined inclusion level of 0.5% of diet. An additional diet contained 0.5% of a mixture of n‐3 highly unsaturated fatty acids (HUFA). The fatty acid profile of hepatopancreas and muscle of shrimp reflected the profile of the diets. HUFA of the n‐3 family showed higher nutritional value than LOA or LNA for juvenile L. vannamei by producing significantly (P < 0.05) higher final weight and weight gain. Neither LOA nor LNA, alone or in combination, improved growth significantly compared with shrimp fed the basal diet.Thus, dietary requirements for LOA and LNA were not demonstrated under these experimental conditions.     

Replacement of fish oil with a DHA‐rich Schizochytrium meal on growth performance,activities of digestive enzyme and fatty acid profile of Pacific white shrimp (Litopenaeus vannamei) larvae

This trial was conducted to evaluate the effects of replacing dietary fish oil with Schizochytrium meal for Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Six test microdiets were formulated using Schizochytrium meal to replace 0 g/kg, 250 g/kg, 500 g/kg, 750 g/kg, 1000 g/kg or 1500 g/kg fish oil DHA. No significant differences were observed in survival, growth, final body length and activities of digestive enzyme among shrimp fed different diets (p > .05). No significant differences were observed in C20:5n‐3 (EPA) in muscle samples (p > .05). C18:3n‐3 and C20:4n‐6 in muscle increased as Schizochytrium meal replacement level increased (p < .05). No significant differences were observed in C22:6n‐3 (DHA) and n‐3 fatty acids among shrimp fed diets that algae meal replaced 0 g/kg ‐ 1000 g/kg of fish oil. Shrimp fed diet R150 had higher DHA content than other groups and had higher n‐3 fatty acids than that of shrimp fed diets R50, R75 and R100 (p < .05). C18:2n‐6, PUFA and n‐6 fatty acids in muscle increased, while n‐3/n‐6 ratio decreased with increasing algae meal replacement level from 0 g/kg to 1000 g/kg (p < .05). In conclusion, Schizochytrium meal could replace 1500 g/kg fish oil DHA in the microdiets without negatively affecting shrimp larvae survival, growth and activities of digestive enzyme.     

Effects of dietary soy isoflavones on growth,antioxidant status,immune response and resistance of juvenile grass carp (Ctenopharyngodon idella) to Aeromonas hydrophila challenge

The current study was conducted to evaluate the effect of dietary soy isoflavones (SI) on growth performance, antioxidant status, immune response and resistance to Aeromonas hydrophila in juvenile grass carp (Ctenopharyngodon idella). Six diets were formulated to contain 0 (control), 10, 50, 100, 500 or 1,000 mg SI per kg feed. Each diet was randomly allotted to triplicate net cages, and each net cage was stocked with 30 fish. The fish were fed one of the experimental diets to satiation twice per day for 60 days. The results showed that the WGR and DGC of the 500 mg/kg SI‐supplemented group were significantly higher than those of the non‐SI‐supplemented group (p < .05). Serum LZM and IgM activities in the SI‐supplemented groups were improved compared to the control group. SOD and GSH‐Px levels of fish fed the diet containing 500 mg/kg SI were significantly enhanced compared to those of fish fed the control diet (p < .05). Additionally, serum CAT, GSH‐Px and AKP activities in 50, 100 and 500 mg/kg SI‐supplemented groups were significantly higher than that in the control group (p < .05). The expression of most immune‐related genes (including IFN‐γ2, TNF‐α, M‐CSF2, IL‐6, IL‐12p40 and IL‐4) was significantly affected by dietary supplementation of SI. The group fed with 500 mg/kg SI had the highest 7‐day cumulative survival rate after challenge test (p < .05). The current results revealed that dietary inclusion of SI could improve the immune response and resistance against A. hydrophila and the supplementation level is suggested to be 500 mg/kg diet.     

Requirements for n-3 highly unsaturated fatty acids in feeding juvenile Iranian sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>) and its effects on growth,carcass quality,and fatty acid composition

A 60-day feeding experiment was carried out on juvenile Iranian sturgeon (Acipenser persicus) to evaluate the effects of different percentages of canola oil and fish oil containing n-3 highly unsaturated fatty acids (n-3 HUFA) on fish growth and fatty acid composition. The requirement for n-3 HUFA of juvenile Iranian sturgeon (48.4 ± 1.98 g) was studied by feeding the fish with various diets containing six different percentage of n-3 HUFA ranging from 1.56 to 17.25 (% of total fatty acids). Neither the weight gain, feed conversion ratio, condition factor, specific growth rate nor the protein efficiency ratio showed any significant differences between the dietary treatments nor in the body composition of juvenile Iranian sturgeon (P > 0.05); also there were no significant difference with respect to the effect of the dietary treatment (P > 0.05) on the blood parameters, for the content of plasma protein, glucose, cholesterol, and triglyceride. The fatty acid composition of the carcass of the Iranian sturgeon fed with the diets containing various levels of n-3 HUFA was reflected by the dietary fatty acid composition. The content of n-3 HUFA in the fish increased with an increase in dietary n-3 HUFA levels. The results indicate that the dietary n-3 HUFA had no effect on the growth of juvenile Iranian sturgeon.     

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%.     

Dietary calcium requirement of red swamp crayfish (Procambarus clarkia)

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

The effects of dietary HUFA level on flame angelfish (Centropyge loriculus) spawning,egg quality and early larval characteristics

This study was conducted to determine the effects of dietary highly unsaturated fatty acids (HUFA) on flame angelfish (Centropyge loriculus) reproduction, and egg and larval quality. In the experiment, formulated diets containing 1.8, 2.9 or 3.6% n‐3 HUFA were fed to flame angelfish broodstock (n = 4) for 5 months. Mean fecundity (daily egg production), egg fertilization rates and embryo viability were used as indicators of egg quality. In addition, mean egg diameter, oil globule diameter, per cent hatch, larval size at hatch, per cent survival to yolk exhaustion and larval size at yolk exhaustion were recorded for each treatment. Flame angelfish fed the diet containing 3.6% n‐3 HUFA exhibited significantly increased fecundity, fertilization rates and embryo viability than fish that were fed the other two formulated diets. Egg diameter, egg oil globule diameter, larval size at hatch, larval survival to yolk exhaustion and larval size at yolk exhaustion from the 3.6% n‐3 HUFA broodstock treatment group were not significantly different from those derived from the Control broodstock treatment. These data revealed that flame angelfish egg quality could respond rapidly (within weeks) to maternal dietary changes. Results from this study further support that dietary HUFA composition can significantly affect broodstock reproductive performance as well as subsequent performance of eggs and larvae.     

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.     

Evaluation of Schizochytrium meal in microdiets of Pacific white shrimp (Litopenaeus vannamei) larvae

A feeding trial was conducted to assess the effects of dietary Schizochytrium meal supplementation on survival, growth performance, activities of digestive enzymes and fatty acid composition in Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Four isonitrogenous and isolipidic diets were formulated to contain graded levels of Schizochytrium meal: 0% (S0, the control diet), 2% (S2), 4% (S4) and 6% dry matter (S6). Results showed that there was no significant difference in survival of shrimps among dietary treatments (P > 0.05). Shrimps fed diets with 2% and 4% microalgae meal had significantly higher specific growth rate (SGR) than that of shrimps fed diets with 0% and 6% microalgae meal, and no significant differences were observed between shrimps fed diets with 2% and 4% microalgae meal (P > 0.05). Activity of trypsin in the pancreatic and intestinal segments, and activity of amylase in the pancreatic segments were not significantly affected by dietary microalgae meal levels (P > 0.05). Specific activities of both alkaline phosphatase and leucine‐aminopeptidase in intestine and purified brush border membrane of intestine were significantly higher in shrimps fed diet with 2% microalgae meal (P < 0.05). There were no significant differences in C18:2n‐6, n‐3 fatty acids, n‐6fatty acids, PUFA and n‐3/n‐6 in muscle samples among dietary treatments. C16:1n‐7, C18:1n‐9, MUFA, C18:3n‐3 and C20:5n‐3 decreased, however, C20:4n‐6 increased in the muscle as dietary microalgae meal level increased. In conclusion, 4% Schizochytrium meal in microdiets of shrimps can improve growth performance and may be a valuable additive in the microdiets of shrimps.