Intestinal epithelium of juvenile dourado Salminus brasiliensis (Cuvier, 1816) fed diet with lyophilized bovine colostrum

The aim of this study was to evaluate the effect of lyophilized bovine colostrum (LBC) used as partial source of dietary protein on the histological characteristics of the intestinal epithelium of juvenile dourado Salminus brasiliensis. Juveniles were fed diets containing 0%, 10% or 20% of LBC inclusion for either 30 or 60 days. For the histological study, the intestine was divided into three segments, S1, S2 and posterior intestine. In the S1 segment, interaction between treatment and period was observed in the number of goblet cells containing sialomucin, effect of treatment in the total number of goblet cells and effect of period in the number of goblet cells containing sulphomucins (P < 0.05). In the S2 segment, effect of period was observed in the number of goblet cells containing acid, neutral and total mucins, sialomucins and the partial volume of the absorptive mucosa (Vv) (P < 0.05). In the posterior intestine, effect of period was observed in the thickness of muscle layer and number of goblet cells containing sialomucins and sulphomucins (P < 0.05). Considering the aspects studied, the presence of 0%, 10% or 20% of LBC in the diet did not significantly influence the enteric histological characteristics of juvenile dourado during the period of the study.     

Juvenile Atlantic salmon decrease white trunk muscle IGF‐1 expression and reduce muscle and plasma free sulphur amino acids when methionine availability is low while liver sulphur metabolites mostly is unaffected by treatment

We previously reported that juvenile Atlantic salmon with mean initial BW 11.5 g offed a methionine deficient diet had lower weight gain due to a reduced protein accretion, while lipid gain was unaffected. Muscle of the fish fed the methionine deficient diet was depleted for sulphur amino acids, while in liver, the concentration of these metabolites was maintained within narrow limits. We speculated whether this could be due to an increased muscle proteolysis to support a prioritized liver metabolism in fish fed the low methionine diets. In this study, we assessed whether genes associated with muscle proteolysis increased under methionine deficiency. The composition of the diets was similar to those used previously containing 1.6 or 2.1 g Met/16 g N. We confirmed that the fish fed the low methionine diet gained less protein compared to fish fed the DL‐methionine enriched diet (P = 0.014), but growth did not reduce significantly. Also the deficient fish maintained the concentrations of liver sulphur amino acids and reduced muscle free methionine. Several of the other free amino acids within muscle increased. Further, methylation capacity was maintained in liver but reduced in the muscle (P = 0.78 and 0.04, respectively). Gene expression of muscle IGF‐1 was lower (P = 0.008) and myosin light chain 2 tended (MLC2, P = 0.06) to be reduced in fish fed low methionine diet, concurrently the activity of cathepsins B+L increased (P = 0.047) in muscle of fish fed the low methionine diet. Gene expression of the muscle‐specific E3 ubiquitine ligases (Murf and MaFbx) was not affected by treatment. Thus, the lower protein gain observed in fish fed the low methionine diet may be caused by reduced protein synthesis in line with the reduced IGF‐1 gene expression in the white trunk muscle. Thus, to support metabolism, the dietary protein needs to be balanced in amino acids to support metabolism in all compartments of the body and secure maximal protein gain.     

Dietary threonine requirement of juvenile large yellow croaker,Larmichthys crocea

A feeding trial was conducted to determine the dietary threonine requirement of juvenile large yellow croaker (Larmichthys crocea). Six diets were formulated containing 45% crude protein with six graded levels of threonine (0.71–2.46% in about 0.35% increment). Each diet was randomly assigned to triplicate groups of 60 juvenile fish (initial body weight 6.00 ± 0.10 g). Fish were fed twice daily (05:00 and 16:30) to apparent satiation for 8 weeks. The result indicated that significant difference was observed in the weight gain among all treatments. Specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and nitrogen retention (NR) increased with increasing levels of threonine up to 1.75% diet (P < 0.05), and thereafter, declined. No significant differences in body dry matter, crude protein, crude lipid or ash content were found among dietary treatments. Theronine contents of fish muscle were significantly affected by dietary threonine levels (P < 0.05). Fish fed the diet with 0.71% threonine showed the lowest threonine content (2.94%) in fish muscle, while fish fed the diet with 1.75% threonine had the highest value (3.16%). Other essential amino acid contents of muscle were not significantly different among the dietary treatments. On the basis of SGR, FE or NR, the optimum dietary threonine requirements of juvenile L. crocea were estimated to be 1.86% of diet (4.13% of dietary protein), 1.90% of diet (4.22% of dietary protein) and 2.06% of diet (4.58% of dietary protein), respectively, using second‐order polynomial regression analysis.     

Dietary supplementation of lysine and/or methionine on performance, nitrogen retention and excretion in pacu Piaractus mesopotamicus reared in cages

A study was conducted to evaluate the effect of dietary supplementation of lysine and/or methionine on growth performance, nitrogen retention and excretion in pacu juveniles reared in cages. Five diets were prepared; four diets based on plant ingredients containing 23% digestible protein (DP), basal: Lys- and Met-deficient, 23L: basal supplemented with lysine only, 23M: basal supplemented with methionine only, and 23LM: basal supplemented with both amino acids and a protein-bound AAs diet based on fish and soybean meal, containing 30% DP. Survival, specific growth rate, protein efficiency rate and feeding cost were not influenced by the dietary treatments (P > 0.05). Fish fed basal diet showed the lowest mean of N retention. Fish fed 30DP diet showed the best results of weight gain (WG) and apparent food conversion rate (FCR) among the dietary treatments. On the other hand, WG in the 23LM group and FCR in the 23LM and 23M groups were not significantly different from the group fed 30DP diet, and showed the highest mean of N retention. There was higher N excretion (P < 0.05) when the fish were fed 30DP and 23L diets than the other dietary treatments. Fish fed plant protein-based diets containing 23% DP supplemented with both amino acids or methionine alone showed satisfactory growth and N retention results when compared with fish fed 30DP diet, with the advantage of lower N emissions into water. The results also evidence the pacu's great potential to be reared in cages.     

Growth performance of juvenile pacu (Piaractus mesopotamicus) and dourado (Salminus brasiliensis) fed with lyophilized bovine colostrum

Growth performance was evaluated in juvenile pacu (Piaractus mesopotamicus) and dourado (Salminus brasiliensis) fed diets containing 0%, 10% and 20% of lyophilized bovine colostrum for 60 days. The performance variables of weight gain, relative weight gain, feed intake, feed conversion ratio, specific growth rate, total protein intake and protein efficiency ratio were evaluated as well as apparent digestibility coefficients of protein and energy in the diets. Inclusion of bovine colostrum did not induce differences in the performance of pacu and dourado (P > 0.05), indicating that the diets were adequate and met the nutritional needs of the juveniles. The protein digestibility in both species was improved with the inclusion of the bovine lacteal secretion. Based on the variables studied, the diets with lyophilized bovine colostrum inclusion were nutritionally suitable for both pacu and dourado indicating the possibility to use this lacteal secretion as a partial substitute of dietary protein.     

Effects of replacing fish meal with mussel (Cristaria plicata) meat on growth,digestive ability,antioxidant capacity and hepatic IGF‐I gene expression in juvenile Ussuri catfish (Pseudobagrus ussuriensis)

An 8‐week feeding trial was implemented to evaluate the effects of replacing fish meal (FM) with mussel (Cristaria plicata) meat (MM) on growth, digestive ability, antioxidant capacity and hepatic insulin‐like growth factor I (IGF‐I) gene expression of juvenile Ussuri catfish (Pseudobagrus ussuriensis). Three isonitrogenous and isolipidic diets were formulated to include 0, 177.5 and 355.1 g/kg of MM, accordingly, replacing 0% (M₀, control), 50% (M₁) and 100% (M₂) of FM protein, respectively. The results showed that the final body weight, weight gain, specific growth rate and feed intake were gradually decreased with dietary MM protein levels increased, but there were no significant difference between M₀ and M₁ groups (p > 0.05). The protein efficiency ratio was increased significantly with dietary MM inclusion (p < 0.05). The apparent digestibility coefficient of dry matter, crude lipid and gross energy gradually increased with increasing dietary MM protein levels, but the apparent digestibility coefficient of crude protein was not significantly affected by MM protein supplementation (p > 0.05). Fish fed diet, M₀ and M₁ remained unaffected significantly on activities of alpha‐amylase and pepsin (p > 0.05), but fish fed diet M₂ had the highest activities of alpha‐amylase and pepsin. Fish fed diet M₁ or M₂ had significantly lower hepatic total antioxidant capacity, superoxide dismutase and the higher malondialdehyde level compared to fish fed diet M_0. In addition, no significant difference was observed in hepatic IGF‐I gene expression level for fish fed diet M₀ and diet M₁, and fish fed diet M₂ showed significantly lower hepatic IGF‐I gene expression level. Therefore, we can conclude that MM protein can successfully substitute 50% of FM protein without significantly negative effect on growth, nutrient utilization, and hepatic IGF‐I gene expression for juvenile Ussuri catfish, but the antioxidant capacity was negatively affected in the present study, what is more, the total replacement of FM by MM in diet may result in the inhibition of the growth and antioxidant capacity of fish.     

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.     

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 Protein and Lipid Levels in Practical Diets on Growth and Body Composition of Tongue Sole,Cynoglossus semilaevis Gunther

A 9‐wk feeding experiment was conducted to estimate the optimal dietary protein and lipid levels for tongue sole, Cynoglossus semilaevis Gunther (initial average weight of 43.8 ± 0.18 g). Six practical test diets were formulated to contain three protein levels (45, 50, and 55%, respectively) at two lipid levels (12 and 16%, respectively) with P/E ratios ranging from 87.1 to 110.5 mg protein/kcal. Each diet was randomly fed to triplicate groups of 20 fish per tank (1000 L). The results showed that fish fed the diet with 55% protein and 12% lipid (P/E ratio of 110.5 mg protein/kcal) had the highest thermal‐unit growth coefficient (TGC), feed efficiency ratio, protein productive value, and energy retention. TGC was significantly increased with increasing dietary protein levels irrespective of dietary lipid levels (P < 0.05). However, fish fed the diet with 16% lipid showed significant lower growth than fish fed the diet with 12% lipid. These results suggest that the diet containing 55% protein and 12% lipid with P/E of 110.5 mg protein/kcal is optimal for tongue sole and the increase of dietary lipid level has no effective protein‐sparing effect.     

Effects of dietary inclusion of soybean meal and cholesterol on the growth,cholesterol status and metabolism of the giant grouper (Epinephelus lanceolatus)

The study evaluated effects of cholesterol supplementation in a diet with high soybean meal (SBM) on the growth and cholesterol metabolism of giant grouper (Epinephelus lanceolatus). All‐fish‐meal diet was used as control. The diet including SBM (replaced 50% of the fish meal protein, SBM diet) and the SBM diet supplemented with 10 g/kg cholesterol (SBM + cholesterol) were used as experimental diets. Three diets were each fed to triplicate groups of juvenile grouper (initial body weight: 12.39 ± 0.36 g) in a recirculating aquaculture system for 8 weeks. Grouper fed the control diet showed higher (p < .05) weight gain, feed intake, feed efficiency and protein efficiency ratio than the other two dietary treatments. Hepatic cholesterol concentrations and 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase gene expressions were higher in fish fed the control diet than fish fed the control diet and SBM + cholesterol diet. Hepatic cholesterol 7α‐hydroxylase gene expression was higher in fish fed the SBM + cholesterol diet than that in fish fed the control diet. Results indicate that giant grouper on a diet low in cholesterol can regulate cholesterol synthesis, suggesting that the reduced dietary cholesterol intake in the fish fed diet containing SBM is sufficiently compensated by increased cholesterol synthesis.     

Effects of replacing dietary fish oil and squid liver oil with vegetable oils on the growth,tissue fatty acid profile and total carotenoids of the giant freshwater prawn, Macrobrachium rosenbergii

A feeding trial was conducted to investigate the complete substitution of either fish oil (FO) or squid liver oil (SLO) with crude palm oil (CPO), canola oil (CO) sunflower oil (SFO) or linseed oil (LO), as the sole added lipid source in diets fed to triplicate groups of giant freshwater prawn, Macrobrachium rosenbergii (initial weight = 0.42 ± 0.01 g) for 6 weeks. Prawns fed the CO or SLO diets showed significantly higher (P < 0.05) specific growth rate than those fed the FO or CPO diets. The feed conversion ratio of the prawns was significantly better when fed the CO diet, compared with the FO, CPO, SFO and LO diets. The muscle eicosapentaenoic acid content of prawns fed the vegetable oil (VO) diets were not significantly different (P > 0.05) from those fed the FO diet, although all VO‐based diets led to a significantly lower docosahexaenoic acid content compared with prawns fed the FO or SLO diet. The whole‐body total carotenoid content was significantly lower for prawns fed the SLO diet compared with prawns on the CO or CPO diets. The successful use of VO instead of marine‐based oils in prawn diets will likely reduce feeding costs associated with M. rosenbergii aquaculture.     

Histochemical distribution of intestinal enzymes of juvenile pacu (Piaractus mesopotamicus) fed lyophilized bovine colostrum

Enzyme activity was evaluated in the intestine of juvenile pacu, Piaractus mesopotamicus, fed diets containing 0, 10 or 20 % of lyophilized bovine colostrum (LBC) inclusion for either 30 or 60 days. The enzymes intestinal acid and alkaline phosphatase (ACP and ALP, respectively), nonspecific esterase (NSE), lipase (LIP), dipeptidyl aminopeptidase IV (DAP IV) and leucine aminopeptidase (LAP) were studied using histochemistry in four intestinal segments (S1, S2, S3 and rectum). Moderate activity of the DAP IV was detected in the three last intestinal segments, but no differences among the treatments were detected. Enzymes LAP, NSE and LIP were weakly stained in all intestinal segments and the inclusion of 10 or 20 % of LBC in the diet commanded a moderate reaction to NSE in the S3 segment at day 60. ACP activity was detected only in the brush border of the S1 segment of fish fed 0 % LBC for either 30 or 60 days. The activity of ALP was very strong in the first intestinal segment, but a weak reaction was seen in the last segments. The inclusion of 20 % of LBC changed the pattern of staining to the ALP, eliciting moderate staining in S2 at day 30 and S1 at day 60. The consumption of diets containing LBC by juvenile pacu did not have significant implications in intestinal enzymatic activity, which still was not fully stimulated.     

Effects of dietary manganese on growth and tissue manganese concentrations of juvenile gibel carp,Carassius auratus gibelio

A 68‐day growth trial was conducted in a flow‐through system to determine the effect of dietary manganese levels on growth and tissue manganese concentration of juvenile gibel carp (Carassius auratus gibelio). Seven purified diets containing 7.21, 8.46, 9.50, 10.50, 13.03, 19.72 and 22.17 mg manganese (as manganic sulfate) per kilogram diet were fed to triplicate groups of fish (initial weight 3.21 ± 0.01 g). The results showed that dietary manganese levels did not significantly affect feed intake of the fish. Specific growth rate, feed efficiency, total hepatic superoxide dismutase activity, carcass and skeletal manganese concentration increased significantly with increased dietary manganese(P < 0.05) while condition factor decreased significantly(P < 0.05). It was concluded that dietary requirement of manganese was 13.77 mg Mn per kilogram diet. Carcass and skeletal manganese concentration could also be used to evaluate the manganese requirement. Total hepatic superoxide dismulase activity was not a sensitive indicator for dietary requirement.     

Dietary Biotin Requirement of Fingerling Catla catla (Hamilton) Based on Growth,Feed Conversion Efficiency,and Liver Biotin Concentration

A 12‐wk experiment was conducted to determine the dietary biotin requirement of the fingerling Catla catla (7.9 ± 0.37 cm; 3.5 ± 0.12 g). Eight diets (35% crude protein, 16.72 kJ/g gross energy) with different levels of biotin (0, 0.05, 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5 mg/kg diet) were fed to triplicate groups of fish to apparent satiation. Highest percent weight gain, protein retention efficiency, and best feed conversion ratio were observed in fish fed 0.5 mg biotin per kg diet. However, fish fed diets containing dietary biotin of 1.0, 1.5, 2.0, and 2.5 mg/kg did not show significant (P > 0.05) differences compared to those fed on dietary biotin of 0.5 mg/kg. Hematological indices, including hematocrit value, hemoglobin content, and red blood cell counts were found to be directly proportional (P < 0.05) to the dietary biotin levels up to 0.5 mg/kg, beyond which a plateau was recorded. Pyruvate carboxylase activity (PCA) was also found to increase with the incremental levels of dietary biotin up to 0.5 mg/kg and further increasing dietary biotin concentration led to stagnation in PCA of fish. Liver biotin concentrations responded positively (P < 0.05) until saturation, which occurred at 1.0 mg/kg diet. Broken‐line analysis of percent weight gain, protein retention efficiency, PCA, and liver biotin concentrations demonstrated that fingerling C. catla require biotin in the range of 0.41–0.87 mg/kg diet.     

Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctutus Fed Diets With and Without Animal Protein for Three Growing Seasons1

An experiment was conducted to determlne the long-term effects of an all-plant-protein diet on production characteristics (harvest yield, dressing percentage, and body composition) of catfish Ictalurus punctatus taken from top-harvested, multiple-stocked ponds over a 2.5-yr period of continuous production. Fish in eight 0.08-ha ponds were fed an extruded, 32% protein control diet (CON) containing animal and plant proteins, while fish in eight replicate ponds were fed an isonitrogenous diet containing only plant proteins, primarily from cottonseed meal and soybean meal (APP). Diets were fed once dally to apparent satiation during the growing season. Ponds were top-harvested twice per year in the spring and fall and partially restocked after each harvest. CON-fed fish received 13,335 kg of feed during the 2.5-yr period. APP-fed fish received 13,506 kg of feed. Total yields were 5,562 kg of CON-fed fish and 5,840 kg of APP-fed fish; average annual yields were 3,477 kgha per yr and 3,650 kgha per yr, respectively (P > 0.05). Feed conversion ratios, 2.5 for CON-fed fish and 2.6 for APP-fed Ash, did not differ significantly (P > 0.05). Live weights at harvest averaged 529 g (CON) and 481 g (APP), and were not significantly different. Dressing percentages were 59% for fish fed both diets (P > 0.05). APP-fed fish had less (P < 0.05) visceral fat and less (P < 0.05) muscle lipid than CON-fed fish. Results indicate that a lysine supplemented, all-plant-protein diet containing 40% cottonseed meal and 20% soybean meal is suitable for long-term production of channel catfish in earthen ponds and such a diet can reduce the fat content of pond-reared fish.     

Effects of Different Dietary Lipid Sources on Growth Performance,Fatty Acid Composition,and Antioxidant Enzyme Activity of Juvenile Rockfish,Sebastes schlegeli

This study was carried out to investigate and compare the effects of various dietary lipid sources on growth performance, body composition, fatty acid profiles, and hepatic and plasma antioxidant enzyme activities of juvenile rockfish, Sebastes schlegeli. Three replicate groups of fish (initial mean weight, 1.7 ± 0.04 g) were fed four isonitrogenous and isolipidic diets containing either fish oil (FO), soybean oil (SO), linseed oil (LO), or a mixture of SO and LO (SO + LO) for 8 wk. There were no significant differences in survival, weight gain, feed efficiency, and protein efficiency ratios of fish fed the diets containing different lipid sources (P > 0.05). The fatty acids compositions of the liver and muscle tissues reflected the dietary fatty acid compositions. Liver and muscle of fish fed the SO diet had high concentration of linoleic acid, whereas those of fish fed the LO diet were rich in linolenic acid. Liver and muscle of fish fed the FO diet had significantly (P < 0.05) higher levels of eicosapentaenoic acid and docosahexaenoic acid than those of fish fed the SO and LO diets. Dietary lipid source had no significant effect on the hepatic and plasma enzyme activities of superoxide dismutase and glutathione peroxidase. The results of this study suggest that SO and LO can be used as a replacement for FO in the diets of juvenile rockfish without incurring any negative effects on growth, feed utilization, and antioxidant enzyme activity, when the dietary essential fatty acid requirements are satisfied for rockfish.     

Effect of tributyrin supplementation in high‐soya bean meal diet on growth performance,body composition,intestine morphology and microbiota of juvenile yellow drum (Nibea albiflora)

Six equal‐protein and equal‐lipid diets were formulated: the fish meal (FM) diet, the soya bean meal (SBM) diet with 40% of FM protein replaced by SBM protein and tributyrin (TB) diets with 0.05% (TB0.05), 0.10% (TB0.1), 0.20% (TB0.2) and 0.40% (TB0.4) tributyrin supplemented in the SBM‐based diet. Each kind of diet was randomly fed to triplicate tanks with 20 fish per tank. Fish were fed apparent satiation twice daily for 56 days. No significant difference in weight gain rate (WGR) and feed efficiency rate (FER) was observed between fish fed the FM, TB0.1 and TB0.2 diets (p > .05). Muscle histidine and arginine proportion of fish fed TB0.1 diet was significantly higher than that of fish fed the SBM diet (p < .05). Intestine morphology results indicated that the supplementation of 0.1% tributyrin significantly improved the mucosal fold height, microvilli length and microvilli density when compared with those of fish fed the SBM diet (p < .05). The supplementation of dietary tributyrin suppressed the pro‐inflammatory gene expression, which may be due to the improvement of physical barrier and modification of microbial communities, such as Acinetobacter, Rhodocyclaceae, Brevundimonas, Sphingopyxis, Hydrogenophaga, Methyloversatilis and Devosia. In conclusion, dietary 0.1% tributyrin supplementation in high‐soya bean meal diet improved growth performance, flesh quality and intestinal morphology structure integrity of yellow drum.     

Optimization of the supplemental essential amino acids to a fish meal-free diet based on fermented soybean meal for rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

To minimize the supplemental essential amino acids (EAAs) to a fish meal-free diet for rainbow trout Oncorhynchus mykiss, four types of fish meal-free diets and a control fish meal-based diet were fed to triplicate groups of trout (initial BW, 16 g) for 10 weeks. Two fish meal-free diets based on a fermented and an unfermented soybean meal were unsupplemented with EAAs (diet FSBM and SBM), and two fish meal-free diets based on the fermented soybean meal were supplemented with a combination of lysine and methionine (diet F + ML) and all EAAs (diet F + All), the EAA contents of which were lower than those of the control diet (diet FM). Although physiological conditions such as the biliary bile acid status and morphological features of fish fed diet FSBM were improved and similar to those of fish fed diet FM, the growth performance was not significantly different (P > 0.05) from fish fed diet SBM. The growth performances and whole body protein contents of fish fed F + ML and F + All diets were similarly improved compared to fish fed diet FSBM. These findings indicate that supplementation of lysine and methionine to a fermented soybean meal-based fish meal-free diet is enough to maximize the amino acid utilization of the diet.     

Effect of dietary canthaxanthin on the growth and lipid composition of red porgy (Pagrus pagrus)

A 24‐week feeding trial was conducted to study the possible effect of dietary canthaxanthin on red porgy growth and lipid composition. Two triplicate groups were established to test two experimental diets: (1) Control group fed a diet with no added carotenoids, and (2) canthaxanthin group (CTX100) fed a diet with 100 mg of synthetic canthaxanthin per kilogram of diet (CTX). Final and eviscerated weight were increased (P < 0.05) in the CTX100 treatment. The rest of growth performance parameters were not affected by the CTX diet. Whole‐fish total lipid content was decreased (P < 0.05) in CTX100 fish. In the liver, total lipids were not affected; however, saturated fatty acids in CTX100 treatment were significantly lower together with a higher n‐3 PUFA and a lower n‐6 PUFA, therefore increasing the n‐3/n‐6 ratio. Liver histology of CTX100 fish revealed decreased lipid vacuolization thus, significantly lowering hepatocyte area. In the muscle, total lipids were not affected. Similar to the liver, an increase of n‐3 PUFA and decrease n‐6 PUFA, led to a significant increase of the n‐3/n‐6 ratio. Concerning plasma, only total cholesterol (TC) was significantly affected by the CTX diet. Dietary canthaxanthin has an effect on red porgy lipid composition.     

Dietary copper requirements of juvenile grouper, Epinephelus malabaricus

To quantify dietary copper (Cu) requirements in grouper, Epinephelus malabaricus, copper sulfate was added to the basal diet at 0, 1, 2, 4, 6, 8, 10 and 20 mg Cu/kg diet providing the actual dietary value of 0.11, 1.66, 2.41, 4.37, 6.56, 8.97, 11.03 and 20.05 mg Cu/kg diet, respectively. Each diet was fed to triplicate groups of grouper (initial body weight 13.35 ± 0.01 g) in a recirculated rearing system for 8 weeks. The Cu concentration in rearing water was monitored during the feeding period and ranged from 1.0-1.5 μg/l. Weight gain (WG) and feed efficiency (FE) were higher (P < 0.05) in fish fed diets with 4.37 and 6.56 mg Cu/kg diet than those in fish fed diets with ≥ 11.03 and ≤ 1.66 mg Cu/kg diet. Hepatic thiobarbituric acid reactive substances (TBARS) value was lowest in fish fed diets with 4.37 and 6.56 mg Cu/kg diet, intermediate in fish fed diets with 11.03 and ≤ 1.66 mg Cu/kg diet, and highest in fish fed the diet with 20.05 mg Cu/kg diet. Differences between each of the three groups were statistically significant (P < 0.05). Both hepatic copper-zinc superoxide dismutase (Cu-Zn SOD) and plasma ceruloplasmin activities in fish fell into four groups. Cu-Zn SOD value was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed the diet with 8.97 mg Cu/kg diet, intermediate in fish fed the diet with 20.05 mg Cu/kg diet, and lowest in fish fed the diet with 0.11 mg Cu/kg diet; plasma ceruloplasmin was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed diets with 2.41, 4.37 and 8.97 mg Cu/kg diet, intermediate in fish fed diets with ≥ 11.03 mg Cu/kg diet, and lowest in fish fed diets with ≤ 1.66 mg Cu/kg diet. All values in each of the four groups were significantly different from the values of three other groups (P < 0.05). Analysis by broken-line regression of WG, hepatic SOD activity and TBARS value and linear regression of whole-body Cu retention of the fish indicate that the adequate dietary Cu concentration in growing grouper is about 4-6 mg Cu/kg diet.