Alternative vegetable lipid sources in diets for grouper, Epinephelus coioides (Hamilton): effects on growth, and muscle and liver fatty acid composition

The aim of this study was to investigate the effects of different oils on growth performance and lipid metabolism of the grouper, Epinephelus coioides. Five experimental fish meal‐based isonitrogenous and isolipidic diets were formulated containing either 5.5%‐added fish oil (FO), soybean oil (SBO), corn oil (CO), sunflower oil (SFO) or peanut oil (PO). Each diet was fed to triplicate groups of 20 fish (initial body weight 13.2±0.02 g) grown in seawater at 28.0–30.5 °C for 8 weeks. Fish were fed twice a day to visual satiety. No significant differences in the survival, weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio or hepatosomatic index were found between fish fed the FO or vegetable oils (VO) diets. Dietary lipid sources did not affect whole‐body composition among grouper fed the various diets. Muscle of fish fed the FO diet had significantly higher levels of 14:0, 16:0, 16:1n‐7, 20:5n‐3[eicosapentaenoic acid (EPA)] and docosahexaenoic acid (DHA)+EPA (except for PO fed fish) compared with those of fish fed VO diets. However, the levels of 18:1n‐9, 18:2n‐6 and DHA/EPA ratios in the muscle of fish fed FO diet were significantly lower than those of fish fed the VO diets. The liver of fish fed the FO diet had significantly higher levels of 18:0, 20:5n‐3, 22:6n‐3, n‐3 highly unsaturated fatty acids and DHA+EPA than those of fish fed the VO diets, whereas increases in 18:1n‐9, 18:2n‐6 and mono‐unsaturated fatty acid levels were observed in the liver of fish fed the VO diets.     

Requirements of vitamin C (l-ascorbyl-2-sulphate and l-ascorbyl-2-polyphosphate) and its effects on non-specific immune responses of grouper, Epinephelus malabaricus

An 8‐week feeding trial was conducted to determine two vitamin C derivatives, l ‐ascorbyl‐2‐sulphate (C2S) and l ‐ascorbyl‐2‐polyphosphate (C2PP), to satisfy vitamin C requirement and to test their effects on the non‐specific humoral immune responses of juvenile grouper, Epinephelus malabaricus. C2S and C2PP were each supplemented at 20, 50, 80, 150, 250 and 400 mg kg^?1 diet in the semi‐purified basal diet providing of 7, 16, 28, 55, 86, 142 mg ascorbic acid (AA) equivalent of C2S kg^?1 diet and 4, 9, 15, 31, 49, 75 mg AA equivalent of C2PP kg^?1 diet, respectively. Basal diet without AA supplemented was included as a control. Each diet was fed to triplicate groups of grouper (mean initial weight: 6.69 ± 0.07 g). Fish fed diets with ≥28 mg AA equivalent of C2S or ≥4 mg AA equivalent of C2PP kg^?1 had significantly (P < 0.05) greater weight gain (WG) than fish fed the unsupplemented control diet. Liver AA concentrations were higher in fish fed diets with ≥16 mg AA equivalent of C2S or ≥9 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Alternative pathway of complement activation (ACP) was higher in fish fed diets with ≥55 mg AA equivalent of C2S or ≥15 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Lysozyme activity was higher in fish fed ≥86 mg AA equivalent of C2S or ≥15 mg AA equivalent of C2PP kg^?1 than fish fed the control diet. Analysis by broken‐line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 46.2 mg AA equivalent of C2S kg^?1 diet and 17.8 mg AA equivalent of C2PP kg^?1 diet, and it also indicated that C2S is approximately 39% as effective as C2PP in meeting the vitamin C requirement for grouper. The data suggest that both C2S and C2PP supplementation support non‐specific immune responses of grouper.     

Replacement of fish oil with vegetable oils in diets for jundiá (Rhamdia quelen Quoy and Gaimard 1824): effects on performance and whole body fatty acid composition

The jundiá (Rhamdia quelen) is a siluriform with great potential for aquaculture in South America. Fish oil is a raw material in diets for fish. However, the fisheries that provide fish oil have reached their limit of sustainability. Thus, the use of alternative sources for this ingredient is primordial. The aim of this study was to evaluate the performance and body composition of the jundiá fed with different sources of the vegetable oils. Jundiá (1.0±0.2 g) were fed for 31 days with five isonitrogenous (37%) and isoenergetic (19 kJ g^?1) diets, in which the following oils were added: 50 g kg^?1 corn oil (CO), 50 g kg^?1 fish oil (FO), 50 g kg^?1 linseed oil (LO), 33.4 g kg^?1 fish oil and 16.7 g kg^?1 linseed oil (1/3LO), 16.7 g kg^?1 fish oil and 33.4 g kg^?1 linseed oil (2/3LO). The performance did not show differences between treatments. The final fatty acid profile and n‐3/n‐6 ratio of the fish were highly influenced by the diet. Fish‐fed diets with linseed and/or fish oil showed superior n‐3/n‐6 ratios to the minimal recommended by the World Health Organization; whereas fish fed diets with corn oil showed an inferior value. Albeit in the present study the commercial size of fish was not attained, these results show a clear tendency. The desaturation/elongation capacity was evidenced, in this species, for the first time. Linseed oil can be utilized as a substitute for fish oil in diets of jundiá without affecting their performance and for producing good‐quality fish. However, more studies are necessary to confirm these results for commercial size.     

Restoration of the fatty acid composition of red seabream (Pagrus auratus) using a fish oil finishing diet after grow-out on plant oil based diets

This study evaluated the potential for manipulating the fatty acid composition of juvenile red seabream, Pagrus auratus. Prior to the start of the study, three groups of fish had been reared for 3 months on a fish oil based diet or diets where the added fish oil had been replaced with either canola or soybean oil. In the present study, fish that had previously been fed either the canola or soybean oil diets were fed a fish oil based diet. Three additional treatments included fish being maintained on their original diets of fish oil, canola oil or soybean oil. Fish were fed their respective diets twice daily to apparent satiety for 32 days. Samples of fish from each treatment were collected after 0, 1, 2, 4, 8, 16 and 32 days. Composition and growth of the fish were determined at each sample point. Most treatments showed no differences in growth performance, although fish fed a fish oil diet after previously being fed a soybean oil diet showed slightly better growth. No significant differences among treatments were observed in proximate composition of the fish, although there was a significant increase in total fat and individual fatty acid (g kg^?1 live‐weight) content of the fish from all treatments over the period of the study. No significant changes in the relative fatty acid composition (% of total fatty acids) over time were observed in the three treatments where fish were maintained on their original diets. In contrast, fish that were previously fed either the canola or soybean oil diets and were then fed a fish oil diet had significant changes in both the relative (% of total fatty acids) and absolute (g kg^?1 live‐weight) fatty acid content. Key changes observed included a decrease in the relative levels of polyunsaturated fatty acids (PUFA) such as 18 : 2n ? 6 and 18 : 3n ? 3. Increases in the relative levels of the long‐chain polyunsaturated fatty acids (lcPUFA) 20 : 5n ? 3 and 22 : 6n ? 3 were also observed in both treatments. The rates of absolute (g kg^?1 live‐weight) change/accumulation of these fatty acids followed an exponential equation that differed for each fatty acid in each treatment. Examination of the retention efficiency of specific fatty acids also showed marked differences between fatty acids within treatments and also differences between treatments. Biologically important fatty acids such as 20 : 5n ? 3 and 22 : 6n ? 3 had only moderate retention efficiencies and these were unaffected by treatment. In contrast, the retention efficiencies of 18 : 2n ? 6 and 18 : 3n ? 3 suggested selective retention of these fatty acids when fed fish oil diets, but moderate catabolism when fed the plant oil diets. There were also high retention efficiencies of most saturated and monounsaturated fatty acids suggestive of active retention and/or active synthesis of these fatty acids by the fish. The results of this study, particularly the increases in lcPUFA, support the usefulness of a fish oil based finisher diet for fish raised predominantly on plant oil based diets.     

Effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides

An experiment was conducted to investigate the effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides. Casein–gelatine‐based diets supplemented with 0, 50, 100, 150, 200 and 250 mg kg⁻¹ iron from ferrous sulphate were fed to grouper (mean initial weight: 21.0 ± 0.2 g) for 8 weeks. Weight gain was highest in fish fed the diet supplemented with 100 mg kg⁻¹ iron, intermediate in fish fed diets with 50, 150, 200 and 250 mg kg⁻¹ iron and lowest in fish fed the basal diet. Feed efficiency followed a similar trend except that the lowest value was in fish fed the basal diet and the diet supplemented with 250 mg kg⁻¹ iron. Hepatic iron was highest in fish fed diets supplemented with iron ≥100 mg kg⁻¹, followed by fish fed diet with 50 mg kg⁻¹ iron and lowest in fish fed the basal diet. The whole‐body iron was lowest in fish fed the basal diet but not significantly different from other groups, as judged by anova . Iron supplement to the basal diet had no significant effect on haematological parameters (red blood cell count, haematocrit and haemoglobin), hepatic copper concentration or manganese, zinc concentration in liver and whole body. Broken‐line analysis of hepatic iron indicated that iron supplementation of 100 mg kg⁻¹ satisfied the hepatic iron storage and that further supplementation did not expand the iron status.     

Single or combined effects of fructo‐ and mannan oligosaccharide supplements and Bacillus clausii on the growth,feed utilization,body composition,digestive enzyme activity,innate immune response and lipid metabolism of the Japanese flounder Paralichthys olivaceus

In this study, we examined the effects of the following eight experimental diets, which varied in fructo oligosaccharides (FOS), mannan oligosaccharides (MOS) and Bacillus clausii concentrations, on the Japanese flounder: control diet (no FOS, MOS and B. clausii), diet F (5 g kg⁻¹ FOS), diet M (5 g kg⁻¹ MOS), diet FM (2.5 g kg⁻¹ FOS + 2.5 g kg⁻¹ MOS), diet B (10⁷ cells g⁻¹B. clausii), diet FB (5 g kg⁻¹ FOS + 10⁷ cells g⁻¹B. clausii), diet MB (5 g kg⁻¹ MOS + 10⁷ cells g⁻¹B. clausii) and diet FMB (2.5 g kg⁻¹ FOS + 2.5 g kg⁻¹ MOS + 10⁷ cells g⁻¹B. clausii). Japanese flounder, initially weighing an average of 21 g, were distributed into 24 net cages at a stocking density of 20 fish per cage. Each diet was hand‐fed to three groups of fish twice daily for 56 days. The weight gain rate (WGR) in fish fed diets B, MB and FMB were significantly higher than in fish fed the control diet, where the fish fed diet FMB had the highest WGR. Fish fed any of the diets, except diets F and B, exhibited better feed conversion ratio than those fed the control diet. Diets MB and FMB significantly elevated intestinal protease activity compared with the control diet, but only the diet FMB promoted amylase activity. Feeding diets FB and FMB increased body protein deposition; additionally, feeding diets B, MB and FMB significantly reduced body lipid deposition. Lysozyme (LSZ) activity was significantly higher in fish fed diets B, FB, MB and FMB than in fish fed the control diet. All diets, except diet M, decreased triglyceride (TG) levels compared to the control diet. Low‐density lipoprotein cholesterol levels in fish fed diets F, FB and FMB were significantly lower than in fish fed the control diet. Without exception, no diets affected feeding rate, condition factor, body moisture, ash contents, phagocytic activity of leucocytes or cholesterol or high‐density lipoprotein cholesterol levels. Our results suggest that diets supplemented with FOS, MOS and B. clausii improved growth performance and health benefits of the Japanese flounder more than other diets or the control diet.     

Dietary calcium requirements of juvenile tilapia, Oreochromis niloticus × O. aureus, reared in fresh water

A feeding experiment was conducted to determine the dietary calcium (Ca) requirement for juvenile hybrid tilapia, Oreochromis niloticus × O. aureus reared in nature water. Purified diet supplemented with 0, 1, 2, 3, 4, 5, 7 and 10 g Ca kg⁻¹ diet providing of 0.6, 1.6, 2.6, 3.7, 4.7, 5.5, 7.5 and 10.7 g Ca kg⁻¹ diet, respectively, were fed to tilapia (mean initial weight: 0.52 ± 0.01 g, n = 3) for 8 weeks. Each diet was fed to three replicate groups of fish in a closed, recirculating fresh water rearing system. The rearing water contained 27.1–33.3 mg L⁻¹ Ca. The tilapia fed the diets supplemented with ≥3.7 g Ca kg⁻¹ had significantly (P < 0.05) higher weight gain, when compared with fish fed the diet with ≤1.6 g Ca kg⁻¹. Fish fed the unsupplemented control showed significantly lower weight gain when compared with the other groups (P < 0.05). Bone Ca concentration was highest in fish fed the diets with ≥4.7 g Ca kg⁻¹, intermediate in fish fed the diet with 2.6 g Ca kg⁻¹ and lowest in fish fed the control diet. Scale Ca concentration was higher in fish fed the diets with ≥3.7 g Ca kg⁻¹ than in fish fed the diets with ≤2.6 g Ca kg⁻¹. Serum alkaline phosphatase activity was 36% increased in fish fed the diets with ≥2.6 g Ca kg⁻¹ than fish fed the diets with <1.6 g Ca kg⁻¹. Analysis by broken‐line regression of weight gain, bone and scale Ca concentrations indicated that the adequate dietary Ca concentration for tilapia in water containing 27.1–33.3 mg Ca L⁻¹ was 3.5, 4.3 and 4.2 g Ca kg⁻¹ diet, respectively, supplied as Ca‐lactate.     

Effects of different dietary lipid sources in the diet for Pangasius nasutus (Bleeker, 1863) juveniles on growth performance,feed efficiency,body indices and muscle and liver fatty acid compositions

Four isonitrogenous (300 g kg^?1 crude protein), isoenergetic (21 kJ g^?1) experimental diets were formulated to contain fish oil (FO), soybean oil (SBO), crude palm oil (CPO) and linseed oil (LO), respectively, as the lipid sources, added at 120 g kg^?1 of crude lipid each. The diets were fed by hand to triplicate groups of Pangasius nasutus (Bleeker, 1863) juveniles (mean weight 10.66 ± 0.04 g), to apparent satiation twice daily for 12 weeks. Fish survival rate was 100% among all the treatments. Growth performance (DGR) was similar among fish fed the SBO, CPO and LO diets, but was significantly (P < 0.05) higher in the CPO compared to fish fed the control (FO) diet. Fish fed SBO and CPO diets also recorded significantly (P < 0.05) higher intraperitoneal fat compared to fish fed the control, whereas fish fed the LO diet did not significantly differ from the other treatments. Muscle and liver fatty acid profile of fish from all the treatments generally mirrored the composition of the diets fed and the major fatty acids recorded were 18:3n‐3 and 18:2n‐6 in the tissues of fish fed the LO and SBO treatments, respectively. Results of this study suggests that P. nasutus fed diets containing vegetable oils (especially CPO and SBO) produce better growth performance, without compromising fish survival and feed efficiency compared with those fed a diet containing only FO.     

Optimizing dietary protein sources for Japanese sea bass (Lateolabrax japonicus) with an emphasis on using poultry by‐product meal to substitute fish meal

This study evaluated the potential of using poultry by‐product meal (PBM) to replace fish meal in diets for Japanese sea bass, Lateolabrax japonicus. Fish (initial body weight 8.5 g fish^?1) were fed six isoproteic and isoenergetic diets in which fish meal level was reduced from 400 g kg^?1 (diet C) to 320 (diet PM1), 240 (diet PM2), 160 (diet PM3), 80 (diet PM4) or 0 g kg^?1 (diet PM5), using PBM as the fish meal substitute. The weight gain (WG), specific growth rate, nitrogen retention efficiency, energy retention efficiency and retention efficiency of indispensable amino acids were higher in fish fed PM1, PM2, PM3 and PM4 diets than in fish fed diets C or PM5. The phosphorus retention efficiency was lower in fish fed PM3, PM4 and PM5 diets than in fish fed C, PM1 or PM2 diets. Fish fed diet PM5 had the highest feed conversion ratio, total nitrogen waste output (TNW) and total phosphorus waste output (TPW) among the treatments. No significant differences were found in the hepatosomatic index or body contents of moisture, lipid and ash among the treatments. Fish fed diet C had lower condition factor and viscerosomatic index than those of fish fed PM1, PM3, PM4 and PM5 diets. The results of this study indicate that using fish meal and PBM in combination as the dietary protein source produced more benefits in the growth and feed utilization of Japanese sea bass than did using fish meal or PBM alone as the dietary protein source. The dietary fish meal level for Japanese sea bass can be reduced to 80 g kg^?1 if PBM is used as a fish meal substitute.     

Requirements of vitamin C (L-ascorbyl-2-monophosphate-Mg and L-ascorbyl-2-monophosphate-Na) and its effects on immune responses of grouper, Epinephelus malabaricus

An 8‐week feeding trial was conducted to evaluate two vitamin C derivatives, L‐ascorbyl‐2‐monophosphate‐Mg (C2MP‐Mg) and L‐ascorbyl‐2‐monophosphate‐Na (C2MP‐Na), to satisfy the vitamin C requirement and to test their effects on the immune responses of juvenile grouper, Epinephelus malabaricus. C2MP‐Mg and C2MP‐Na were each supplemented at 20, 50, 80, 150, 250, and 400 mg kg^?1 diet in the basal diet providing of 7, 18, 31, 51, 93, 145 mg ascorbic acid (AA) equivalent of C2MP‐Mg kg^?1 diet and 4, 10, 17, 31, 47, 77 mg ascorbic acid (AA) equivalent of C2MP‐Na kg^?1 diet, respectively. Basal diet without AA supplementation was included as control. Each diet was fed to triplicate groups of grouper (mean initial weight 3.20 ± 0.05 g). Fish fed diets supplemented with either C2MP‐Mg or C2MP‐Na had significantly (P < 0.05) greater weight gain (WG), feed efficiency and survival than those fed the unsupplemented control diet. Liver ascorbate concentrations in fish generally increased as dietary C2MP‐Mg or C2MP‐Na supplementation level increased. Haemolytic complement activity was higher in fish fed diets supplemented with 92 mg AA equivalent of C2MP‐Mg kg^?1 or 10–17 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Lysozyme activity was higher in fish fed ≥51 mg AA equivalent of C2MP‐Mg kg^?1 or ≥47 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Analysis by broken‐line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 17.9 mg AA equivalent of 2MP‐Mg kg^?1 and 8.3 mg AA equivalent of C2MP‐Na kg^?1, and it also indicated that C2MP‐Mg is about 46% as effective as C2MP‐Na in meeting the vitamin C requirement of grouper.     

Effects of dietary supplementation with coconut oil on the growth,fatty acid profiles and some lipid metabolism relative gene expressions of orange‐spotted grouper Epinephelus coioides

This study investigated the effects of coconut oil as a dietary supplement on the growth, lipid metabolism and related gene expressions of juvenile orange‐spotted grouper Epinephelus coioides. Coconut oil at concentrations of 0, 10, 30 and 50 g/kg was used to replace dietary lipids in a basal diet containing 150 g/kg lipids. The four experimental diets were, respectively, fed to triplicate groups of juvenile groupers (initial weight: 8.53 ± 0.13 g) in a recirculating system for 8 weeks. Fish fed the diet containing 50 g/kg coconut oil exhibited lower (p < .05) weight gain than did fish fed the diet containing 30 g/kg coconut oil; however, no significant differences in weight gain were observed between fish fed diets containing 0 and 10 g/kg coconut oil. Hepatic carnitine palmitoyltransferase‐1, fatty acid synthase, fatty acid elongase, fatty acid desaturase and peroxisome proliferator‐activated receptor gamma gene expressions were all the highest in fish fed the diet containing 10 g/kg coconut oil. Fish fed the coconut oil‐free basal diet demonstrated upregulated gene expression of neuropeptide Y. The results suggest that dietary supplementation with 10 g/kg coconut oil exerted beneficial effects on lipid metabolism by E. coioides.     

The effect of feeding diets containing deoxynivalenol contaminated corn on channel catfish (Ictalurus punctatus) challenged with Edwardsiella ictaluri

Channel catfish were fed practical corn‐soybean meal diets for 10 weeks that contained various weighed amounts of ground, dried field corn contaminated with 20 mg deoxynivalenol (DON) kg⁻¹. Weighed amounts of DON corn were blended with weighed amounts of ground, clean corn that contained no DON (0 mg kg⁻¹) to yield five diets that had 0, 2.5, 5.0, 7.5 and 10.0 mg DON kg⁻¹ of diet. Results show that catfish fed diets that contained DON for 7 weeks did not experience lower weight gains or poorer feed conversion ratios that were significantly (P > 0.05) different from control‐fed fish. Mortality of catfish during the 21‐day post‐challenge period indicate that catfish fed diets containing DON‐contaminated corn that provided at least 5.0 mg DON kg⁻¹ of diet had significantly (P < 0.05) lower mortality than catfish fed the control diet or the diet that provided 2.5 mg DON kg⁻¹ of diet. The presence of DON‐contaminated corn in the experimental diets did not significantly (P > 0.05) alter fish body weight gains and appeared to provide a protective effect for channel catfish challenged with the pathogenic bacterium Edwardsiella ictaluri.     

Evaluation of fish-meal free diets for rainbow trout, Oncorhynchus mykiss

Eight experimental diets were formulated for rainbow trout using agricultural byproducts as major ingredients. Each experimental diet contained varying amounts of corn grain, corn gluten meal, corn gluten feed and one of the following: 200 g kg^?1 peanut meal, 200 or 400 g kg^?1 soybean meal (SBM), 390 g kg^?1 low-allergen soy flour, 310 g kg^?1 soy protein concentrate, 300 g kg^?1 low-allergen soy protein concentrate or 200 g kg^?1 SBM + 110 g kg^?1 blood meal. One diet contained 200 g kg^?1 SBM and canola oil as the main lipid source. The remaining diets contained 95 g kg^?1 menhaden oil. Fish fed a commercial trout diet exhibited significantly greater weight gain (322%), and a lower feed conversion ratio (0.89) but significantly lower protein efficiency ratio (2.18) than fish fed the experimental diets. Within the experimental diets, fish fed the 400 g kg^?1 soy flour diet and the 400 g kg^?1 soybean meal diet had significantly higher weight gains (276% and 268%) and protein efficiency ratios (2.58 and 2.52), and lower feed conversion ratios (1.02 and 1.03) than fish fed other experimental diets. Fillet flavour varied between treatments. Most notable was the lower fishy flavour and higher chicken flavour of fish fed the diet that contained canola oil rather than menhaden oil. Microscopic evaluation of the liver and five sections of the gastrointestinal tract failed to demonstrate any differences between treatment groups. The ingredient costs of several experimental diets were lower than the estimated cost of a standard commercial trout diet. However, the superior feed conversion ratios of fish fed the control diet resulted in lower feed costs per unit of fish produced.     

Effects of various corn distillers by‐products on growth,feed efficiency,and body composition of channel catfish,Ictalurus punctatus

A study was conducted to examine the use of corn distillers’ by‐products in diets and the effects of additional dietary fat on channel catfish, Ictalurus punctatus, performance. Juvenile channel catfish (initial weight: 12.6 g per fish) were stocked in flow‐through aquaria and fed one of six practical diets for 9 weeks. Fish fed the control + fat diet consumed more diet and had higher feed efficiency ratio (FER) than fish fed the control diet, but weight gain was not significantly different between fish fed these two diets. Fish fed the diet containing 300 g kg^?1 distillers dried grains with solubles (DDGS) consumed more diet and gained more weight, but had similar FER compared with fish fed the control + fat diet. The diet containing 200 g kg^?1 high‐protein distillers grains (HPDDG) resulted in similar diet consumption, weight gain and FER as the control + fat diet. Fish fed the diet containing 100 g kg^?1 distillers solubles (DS) consumed more diet, but had similar weight gain and FER compared with fish fed the 300 g kg^?1 DDGS diet. The presence of distillers solubles in the diet (300 g kg^?1 DDGS, 100 g kg^?1 DS, 100 g kg^?1 EDS diets) appears to increase diet consumption, weight gain, and FER over the control diets with or without additional fat.     

Effects of dietary soybean oil concentration on growth, nutrient utilization and muscle fatty acid composition of gilthead sea bream (Sparus aurata L.)

A 309 days feeding experiment was carried out on gilthead sea bream fingerlings (initial weight 14.7±4.4 g) to evaluate effects of substitution of fish oil with soybean oil in diets on growth and sensory characteristics and muscle fatty acid composition. Duplicate groups of fish were hand fed with four isoenergetic and isonitrogenous diets (46% protein, 14% lipid and 22 MJ kg⁻¹) in which 0%, 24%, 48% or 72% of the fish oil was replaced by soybean oil. Fish fed diet 72% reached a lower final weight (324 g) than fish fed diets 0%, 24% and 48% (349, 343 and 338 g respectively). Feed intake, protein efficiency ratio, body composition and economic profitability were not influenced by the amount of soybean oil in the diets, but muscle fatty acid composition differed with diets. Panellists observed significant sensory differences between fish fed diet 0% and diet 72%. These results verified the possibility of feeding sea bream until they reached commercial weight with a 48% dietary substitution of fish oil for soybean oil.     

Effects of dietary docosahexaenoic acid sources,microalgae meal and oil,on growth,fatty acid composition and docosahexaenoic acid retention of orange‐spotted grouper,Epinephelus coioides

This study evaluated the effects of Aurantiochytrium spp. microalgae meal and oil as dietary docosahexaenoic acid (DHA) sources on the growth, fatty acid composition and DHA retention of orange‐spotted grouper, Epinephelus coioides. Dietary fish oil was replaced with microalgae meal or oil to provide an equal amount of DHA as a fish oil‐containing basal diet. In total, three experimental diets were fed to triplicate groups of fish (initial wt: 8.48 ± 0.06 g) in a recirculating system for 8 weeks. The weight gain and feed efficiency of the fish did not differ significantly among the experimental diets. The fatty acid composition of the whole body of the fish generally reflected the composition of their diet. The concentration of eicosapentaenoic acid in the whole body was higher in the fish fed the fish meal control diet than in those fed the two experimental diets The fish fed the control diet and those fed the diet containing microalgae oil exhibited higher DHA concentrations than did the fish fed the diet containing microalgae meal. The whole‐body DHA retention was the highest in the fish fed the diet with microalgae oil, followed by the fish fed the control diet. The lowest whole‐body DHA retention was observed in the fish fed the diet containing microalgae meal. The results suggested that the oil from Aurantiochytrium spp. microalgae can be used as DHA source for the grouper. DHA utilization by the fish was higher when the diet was supplemented with microalgae oil than with dry microalgae meal.     

Effect of purified macronutrients on specific dynamic action in carnivorous southern catfish

The effect of purified macronutrients on specific dynamic action (SDA) was assessed in juvenile southern catfish (39.81 ± 1.35 g) at 27.5 °C by stuffing iso‐energetic (5 kJ) casein, corn oil, corn starch in sections of grass carp intestine (0.25 g). A control (without filler) and mixed diets were also made (each macronutrient provide one‐third energy). The postprandial metabolic response, i.e. the oxygen consumption curve, was markedly different among fish fed different food. The peak postprandial metabolic rate of fish fed mixed diet (76.7 mgO₂ h⁻¹) was significantly higher than that of protein group (66.1 mgO₂ h⁻¹), while the latter was significantly higher than those of other groups (56.1 mgO₂ h⁻¹ for lipid, 54.0 mgO₂ h⁻¹ for carbohydrate and 56.1 mgO₂ h⁻¹ for control) (P < 0.05). The SDA durations were 32, 32, 30, 14 and 10 h for mixed, casein, corn oil, corn starch and control groups, respectively. The SDA coefficient (energy expended on SDA as per cent of ingested energy) of casein (9.41%) was significantly higher than that of mixed diet (7.43%) (P < 0.05), while the latter was significantly higher than those of corn oil (3.97%) and corn starch (0.84%) (P < 0.05). The results of this study suggested that the method of using casing on investigation of SDA in carnivorous fish was feasible. The SDA response of carnivorous southern catfish fed protein was higher than lipid while latter was higher than carbohydrate (nearly to zero). The result of this study may give interesting information for understanding the physiological mechanism under SDA.     

Effects of totally replacing dietary fish oil by linseed oil or soybean oil on juvenile hybrid sturgeon,Acipenser baeri Brandt♀×A. schrenckii Brandt♂

The growth performance, body composition, fillet fatty acid content, serum hepatic enzymes and postprandial changes in serum lipid metabolism of hybrid sturgeon (70.8 ± 0.5 g) were investigated to determine the effects of total replacement of 80 g kg^‐1 fish oil (diet A) with linseed oil (diet B) and soybean oil (diet C), respectively. No significant differences in weight gain rate and specific growth ratio were observed among all fish groups (p > .05). Diet A fish group had the highest, but diet B fish group had the lowest feed intake (p < .05). Feed efficiency of fish fed diet A was significantly lower than the other two fish groups (p < .05). Fish fed diet A had the lowest fillet and liver lipid contents (p < .05). Serum lactate dehydrogenase, alanine aminotransferase and aspartate aminotransferase activities of fish fed diet A were significantly lower than those of fish fed diets B and C (p < .05). The contents of linoleic acid (C18:2n6) and linolenic acid (C18:3n3) in fillets showed a significantly positive linear correlation with the diets. Serum glucose and non‐esterified fatty acid were just affected by the time point (p < .05). The lipid source, time point and interaction of both factors had significant effects on serum triglyceride, high‐density lipoprotein cholesterol and low‐density lipoprotein cholesterol (p < .05). Serum total cholesterol was only affected by interaction of time point and lipid source (p < .05), and ketone body was not affected by lipid source, time point or interaction of both factors (p > .05). In summary, total replacement of fish oil with linseed oil or soybean oil had no significant adverse effects on hybrid sturgeon growth during 84‐day period, and linoleic acid and linolenic acid in fillet were modified by dietary treatments.     

Polka-dot grouper, Cromileptes altivelis, can utilize dietary fat efficiently

Polka‐dot grouper, Cromileptes altivelis, a highly‐prized fish in Asian live fish markets, is a slow‐growing species. Long‐chain (LCF) or medium‐chain fatty acids (MCF) were fed to polka‐dot grouper (14 g initial weight) for 8 weeks to see if growth could be stimulated. Five dietary treatments were compared: a control diet with low fat (56 g kg^?1) or diets that contained either moderate (150 g kg^?1) or high (300 g kg^?1) supplements of fat that were added either as olive oil for the LCF or coconut oil for the MCF. Control fish performed well; they grew at 2.2 g week^?1, had a dry matter feed conversion ratio of 1.0 and deposited dietary protein and energy at efficiencies of 25 and 26%. Fish fed LCF at moderate levels performed better than controls but, when fed LCF at high levels or MCF at any level, their performance was inferior to controls. We conclude that dietary supplementation with 150 g kg^?1 of LCF stimulates growth and improves protein retention of polka‐dot grouper whereas higher levels, or the same or higher levels of MCF, depress performance.     

The effect of temperature and dietary fat level on tissue lipid composition in Atlantic salmon (Salmo salar) fed wax ester‐rich oil from Calanus finmarchicus

Copepod oil (CO) from the marine zooplankton, Calanus finmarchicus, is a potential alternative to fish oils (FOs) for inclusion in aquafeeds. The oil is composed mainly of wax esters (WE) containing high levels of saturated fatty acids (SFAs) and monounsaturated fatty alcohols that are poorly digested by fish at low temperatures. Consequently, tissue lipid compositions may be adversely affected in salmon‐fed CO at low temperatures. This study examined the lipid and FA compositions of muscle and liver of Atlantic salmon reared at two temperatures (3 and 12 °C) and fed diets containing either FO or CO, supplying 50% of dietary lipid as WE, at two fat levels (～330 g kg^?1, high; ～180 g kg^?1, low). Fish were acclimatized to rearing temperature for 1 month and then fed one of four diets: high‐fat fish oil (HFFO), high‐fat Calanus oil (HFCO), low‐fat fish oil (LFFO) and low‐fat Calanus oil (LFCO). The fish were grown to produce an approximate doubling of initial weight at harvest (220 days at 3 °C and 67 days at 12 °C), and lipid content, lipid class composition and FA composition of liver and muscle were determined. The differences in tissue lipid composition between dietary groups were relatively small. The majority of FA in triacylglycerols (TAG) in both tissues were monounsaturated, and their levels were generally higher at 3 °C than 12 °C. Polyunsaturated fatty acids (PUFA), particularly (n‐3) PUFA, predominated in the polar lipids, and their level was not significantly affected by temperature. The PUFA content of TAG was highest (～26%) in the muscle of fish fed the HFCO diet at both temperatures. Tissue levels of SFAs were lower in fish‐fed diets containing HFCO than those fed HFFO, LFFO or LFCO, particularly at 3 °C. The results are consistent with Atlantic salmon being able to incorporate both the FA and fatty alcohol components of WE into tissue lipids but, overall, the effects of environmental temperature on tissue lipids were more pronounced in fish fed the CO diets than FO diets.