Effects of dietary fish oil replacement by various vegetable oils on growth performance,body composition and fatty acid profile of juvenile Malaysian mahseer,Tor tambroides

The current study was carried out to investigate the effects of replacing dietary fish oil with different vegetable oil sources and ratios on the growth performance and tissue fatty acid profiles of juvenile Tor tambroides. Three different vegetable oils (sunflower oil, linseed oil and palm oil) were used in two different substitution ratios (50% and 100%). A diet without replacement (100% fish oil) was used as a control. Triplicate groups of T. tambroides juveniles (5.0 ± 0.4 g) were fed the test diets for 9 weeks. The highest weight gain was observed in fish fed palm oil diets that, of course, were reared in aquaria. There was a significant effect (P < 0.05) of the percentage of fish oil replacement on the liver weight after controlling for the effect of fish weight (P < 0.05). The viscera weight significantly increased (P < 0.05) in fish on vegetable oil diets, and its highest amount observed among fish fed palm oil diets. Vegetable oil inclusion significantly reduced eicosapentaenoic acid and docosahexaenoic acid (DHA) concentrations in both muscle and liver of fish except for fish on 50% palm oil diet that had similar liver DHA content with those on control diet.     

Effect of diets containing laurel seed oil on growth and fatty acid composition of rainbow trout,Oncorhynchus mykiss

The aim of this study was to determine the effects of replacing fish oil (FO) with laurel seed oil (LSO), as an alternative plant lipid source in diets on the growth and fatty acid composition of rainbow trout (Oncorhynchus mykiss; 111.47 ± 0.2 g mean individual weight). At the end of the feeding trial, survival was 100% in all treatments. No significant differences were seen in growth between the dietary groups (P > 0.05). The protein, lipid and ash contents were not significantly different among the groups (P > 0.05); however, there was a significant difference in protein and ash content between the treatment groups and the initial, and between the 50LSO group and the initial group, respectively (P < 0.05). The viscerosomatic index (VSI) and hepatosomatic index (HSI) values were not affected by increasing LSO percentages in the diets. The n‐6 polyunsaturated fatty acid (PUFA) concentration increased with increasing LSO levels in the diets. In contrast, the n‐3 PUFA levels decreased with increasing LSO levels in the diets. The liver and muscle were used for the analysis of fatty acids. The highest level of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations was recorded in fillet of fish fed the FO diet and the lowest in those fed the 50LSO diet. However, EPA and DHA ratios in the liver of fish fed the 75LSO diet were higher than those in fillet of fish fed the FO and 50LSO diets. No significant differences were seen in fatty acid composition between the dietary groups (P > 0.05). Based on the results of growth performance and fatty acid composition of the experimental fish in this study, it can be concluded that the 75% concentration of laurel seed oil performed best among the diets tested in the experiment.     

The effect of fish and rapeseed oils on growth performance,egg fatty acid composition and offspring quality of sterlet sturgeon (Acipenser ruthenus)

The aim of this study was to evaluate the long‐term effects (7‐month experiment) of diets consisting of fish oil (Kilka fish) and vegetable oil (rapeseed) on the reproductive performance of sterlet sturgeon (Acipenser ruthenus) broodstock. Forty‐five broodstock (990.3 ± 20.05 g) were randomly allocated to three different diet treatments. Three experimental diets were formulated with graded levels of fish oil (100% FO), vegetable oil (100% VO), and a combination of fish and vegetable oil (50% FO + 50% VO). At the end of the 7‐month feeding trial period, the weight gain and final weight were changed significantly different between the treatments (p < 0.05). Broodstock fed the FO + VO diet had higher growth than those fed the only FO or VO diets (p < 0.05). The highest germinal vesicle migration percentage was observed in FO + VO treatment (p < 0.05). The DHA/EPA, DHA/ARA and EPA/ARA ratios in oocyte exhibited a significant difference in the different treatments (p < 0.05). This study indicates that nutrition of broodstock with diet including FO + VO (p < 0.05) can positively affect the growth performance of larvae compared with only FO or VO diets. Furthermore, the high levels of 18:1n‐9, AL and ALA contents in oocytes from broodstock fed VO and the lowest ALA content in oocytes from broodstock fed FO underlined the important role of broodstock diets in the reproductive process and embryonic and/or larval developments of sterlet.     

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 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.     

Effects of dietary fish oil replacement by microalgae raw materials on growth performance,body composition and fatty acid profile of juvenile olive flounder,Paralichthys olivaceus

Replacing dietary fish oil with DHA‐rich microalgae Schizochytrium sp. and EPA‐rich microalgae Nannochloropsis sp. for olive flounder (Paralichthys olivaceus) was examined. Three experimental isonitrogenous and isolipidic diets with lipid source provided by 50% fish oil (F50S50), 50% (M50F25S25) and 100% microalgae raw material (M100) respectively were compared with a soybean oil (S100) diet as control. Triplicate groups of olive flounder juveniles (16.5 ± 0.91 g) were fed the experimental diets, and a group was fed the control diets for 8 weeks in a recirculation system. Results showed feed efficiency and growth performance were not significantly changed when fish oil (FO) was totally substituted by soybean oil (SO) or microalgae raw material (MRM). The whole‐body composition, lipid content of liver and muscle, and lipid composition of plasma were not significantly influenced by the total substitution of FO by MRM. The polyunsaturated fatty acids (PUFA) content of muscle and liver declined in fish fed S100 diet, whereas it was not significantly reduced in fish fed M50F25S25 and M100 diets. The total substitution of FO by MRM not only maintained the levels of arachidonic acid, EPA or DHA but also increased n‐3/n‐6 ratio. In conclusion, MRM as the sole lipid source is sufficient to obtain good feed efficiency, growth performance and human health value in olive flounder juveniles.     

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.     

Effect of variation in the dietary ratio of linseed oil to fish oil on growth,body composition,tissues fatty acid composition,flesh nutritional value and immune indices in Manchurian trout,Brachymystax lenok

In order to study the effects of linseed oil substitution on the growth, body composition, tissue fatty acid composition, flesh nutritional value and immune indices of juvenile Manchurian trout, five feed types containing different levels of linseed oil (LO) mixed with fish oil (FO) were prepared: 0 (0 LO); 250 g/kg (25 LO); 500 g/kg (50 LO); 750 g/kg (75 LO); and 1000 g/kg (100 LO); and fed to juvenile Manchurian trout (initial weight 6.43 ± 0.02 g) for 9 weeks. The results showed that substitution of FO with 750 g/kg LO did not affect the growth of juvenile trout, with protein content in the dorsal muscle, and lipid content in the liver not showing any significant difference (p > 0.05). The highest lipid content found in muscle samples occurred for the 25 LO diet. The fatty acid composition found in the dorsal muscle and the liver of the Manchurian trout reflects the fatty acid composition in the diet, where the relative amount of linolenic acid (ALA), linoleic acid (LA) and docosahexaenoic acid (DHA) found in these organs has a positive linear correlation with their relative composition in the diet (p < 0.05). As the amount of LO in the diet was increased, the composition of ALA found in the sampled organs increased, while the composition of DHA and eicosapentaenoic acid (EPA) decreased. At the same time, the index of atherogenicity (IA) and thrombogenicity (IT) of the muscle samples from the 75 LO and 100 LO diets was significantly lower than for the 0 LO and 25 LO diets (p < 0.05), while the flesh lipid quality (FLQ) in the 100 LO diet was significantly lower than for the other diets (p < 0.05). The aspartate transaminase (AST) activity decreased initially, and then increased, as the level of LO replacement for FO was increased, with the 25 LO diet being significantly lower than for other groups (p < 0.05). The alanine aminotransferase (ALT) activity in serum samples from the 100 LO diet was higher than that from other diets. The lysozyme (LZM) activity in both serum and liver tissue first increased to a peak for the 25 LO and 50 LO diets, respectively, and then decreased as the level of LO was further increased. There was no significant change in the alkaline phosphatase (AKP) activity in the liver samples; however, the acid phosphatase (ACP) activity decreased significantly from the highest value for 0 LO feed group. In conclusion, the composition of fatty acids in the dorsal muscle and the liver was found to be modified by the diets, and with the diet containing less than 750 g/kg LO, being both beneficial for growth, and improved immunity, while maintaining the nutritional value of the lipid content in the dorsal muscle during the 9‐week period.     

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.     

Effect of replacing dietary fish oil with soybean oil on growth performance,fatty acid composition and haematological parameters of juvenile meagre,Argyrosomus regius

A nutrition trial with meagre, Argyrosomus regius was assessed to determine the effect of dietary replacement of fish oil (FO) by soybean oil (SO) on the growth, feed utilization, body composition, fatty acid composition and basic haematological parameters. Six isonitrogenous (47% crude protein) and isoenergetic (gross energy 22 kJ/g) experimental diets were formulated by replacing 0 (FO), 20 (S20), 40 (S40), 60 (S60), 80 (S80) and 100 (S100) % of the FO with SO. Fish were fed three times daily to near satiation for 14 weeks. The specific growth rate (SGR) of fish fed S100 diet was significantly lower than the other treatments, except SO80 diet. The fish fed SO100 diet displayed significantly higher feed conversion ratio than that of other diets (P < 0.05). It was observed that fish fed the SO100 and SO80 diets displayed haemoglobin (HGB) levels significantly lower (P < 0.05) than fish fed the SO20 diet. Packed cell volume (PCV) of fish fed SO20 diet was significantly higher compared to SO100. The white blood cell (WBC) and red blood cell (RBC) remained unaffected by dietary treatment. The docosahexaenoic acid (22:6n‐3, DHA) and eicosapentaenoic acid (20:5n‐3, EPA) levels of meagre were significantly reduced by the substituting of dietary SO by FO at the end of the feeding period. The level of linoleic acid (18:2n‐6, LA) and linolenic acid (18:3n‐3, LNA) significantly raised in fish fed with SO diets (P < 0.05). The results of this study showed that SO could be replaced FO up to 80% in meagre diet without negative effect on growth performance and basic haematological parameters. Furthermore, the maximum level of FO replacement with SO determined by second order polynomial regression analysis, was 30.1% on the basis of maximum SGR.     

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.     

橡胶籽油替代豆油对草鱼(Ctenopharyngodon idellus)生长性能、消化酶活性及部分生化指标的影响

为研究橡胶籽油替代豆油对草鱼(Ctenopharyngodon idellus)生长性能、消化酶活性、血脂水平、蛋白质代谢及抗氧化功能的影响,分别以橡胶籽油替代0(对照组)、25%、50%、75%和100%豆油配制5种等氮等能饲料,进行10周饲养实验。实验显示,0~50%替代组草鱼增重率、日增重系数显著高于100%替代组(P<0.05)。随着橡胶籽油替代豆油比例的升高,饲料系数呈先下降后上升的趋势,其中,25%替代组饲料系数最低,显著低于50%~100%替代组(P<0.05);25%替代组蛋白质效率最高,显著高于其他处理组(P<0.05)。随着橡胶籽油替代比例的升高,肠道胰蛋白酶、脂肪酶活性呈先上升后下降的趋势,其中,25%替代组脂肪酶活性最高,显著高于其他处理组(P<0.05),50%替代组胰蛋白酶活性最高,显著高于对照组、75%和100%替代组(P<0.05)。0~50%替代组肝胰脏胰蛋白酶活性显著高于75%和100%替代组(P<0.05)。25%~100%替代组血清总胆固醇(TC)含量显著低于对照组(P<0.05)。随着橡胶籽油替代比例的升高,肝胰脏天门冬氨酸氨基转移酶(AST)、丙氨酸氨基转移酶(ALT)活性呈先下降后上升的趋势,其中,25%替代组AST、ALT活性最低,显著低于对照组和100%替代组(P<0.05)。0~25%替代组血浆总抗氧化力(TAC)显著低于75%和100%替代组(P<0.05)。对照组血浆、肝胰脏丙二醛(MDA)含量显著高于100%替代组(P<0.05)。由此可知,橡胶籽油替代25%~50%豆油对草鱼生长性能、饲料利用率、血脂水平、抗氧化功能指标均无不良影响;但替代超过50%时显著降低草鱼生长性能和消化酶活性。     

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

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

Non‐fish meal,non‐fish oil diet development for red sea bream,Pagrus major,with plant protein and graded levels of Schizochytrium sp.: Effect on growth and fatty acid composition

A feeding experiment was conducted to determine the optimal formulation level of algae meal, which is rich in docosahexaenoic acid (DHA), in a non‐fish meal diet. Six iso‐nitrogenous (450 g/kg) and iso‐lipidic (130 g/kg) experimental diets were prepared. The control diet was formulated with fish meal (400 g/kg), fish oil (60 g/kg), plant protein sources (220 g/kg) and rapeseed oil (50 g/kg). Plant protein sources (soy protein concentrate, soybean meal and corn gluten meal), rapeseed and fish oil were formulated in the second diet (NFM + FO). In the third diet, fish oil of the NFM + FO diet was replaced by rapeseed oil (NFM + NFO) and designated as the negative control. In the other three diets, rapeseed oil in the NFM + NFO diet was replaced with algae meal (Schizochytrium sp. powder) at 50 g/kg, 100 g/kg and 150 g/kg (AM5, AM10 and AM15, respectively). Triplicate groups of juvenile red sea bream (8.8 g) were fed the experimental diets for 12 weeks near satiation. The growth was lowest in the fish fed NFM + NFO diet. This was improved by the formulation of algae meal, which reached the growth level of the NFM + FO group in the AM10 group. The lipid content of the whole fish body in the NFM + NFO group was significantly lower than those of other groups. The fatty acid profile showed significant differences among dietary treatments. DHA content in total and polar lipids of the whole body and liver was highest in the AM10 and AM15 groups. These results reconfirm that microalgae are a suitable lipid source for the replacement of dietary fish oil for marine fish, and the optimal level was estimated as 50 g/kg?100 g/kg in diet.     

Effect of dietary fish oil replacement by rapeseed oil on the growth,fatty acid composition and serum non‐specific immunity response of fingerling black carp,Mylopharyngodon piceus

An 8‐week experiment on fingerling black carp Mylopharyngodon piceus was conducted to evaluate the effects of dietary fish oil (FO) supplement on growth, fatty acid composition and non‐specific immunity responses. Five triplicate fingerling groups (initial weight = 2.72 ± 0.35 g) were fed isoenergetic and isonitrogenous diets in which the dietary FO was replaced with rapeseed oil (RO) in graded increments of 25% (0–100%). No significant effects were observed on specific growth rates, survival rates and feed conversion ratios, but there were significant differences in whole body moisture and liver lipid contents (P < 0.05), and the 100% RO replacement diet significantly enhanced hepatosomatic indexes compared to control group (P < 0.05). Other approximate whole body constituents, viscerasomatic ratios and condition factors were not influenced by dietary oil treatments. Fatty acid composition of muscle and liver was influenced by dietary fatty acid input, α‐linoleic acid and γ‐linolenic acid were significantly increased with increasing RO, but eicosapentaenoic acid, docosahexaenoic acid and the n‐3/n‐6 ratio were significantly reduced (P < 0.05). Alternative complement pathway, lysozyme and superoxide dismutase activities were not significantly influenced. These results indicate that black carp fed diets with FO supplement had similar growth and non‐specific immunity to the fish fed diet with RO.     

Effects of dietary fish oil substitution with linseed oil on growth,muscle fatty acid and metabolism of tilapia (Oreochromis niloticus)

This study was conducted to evaluate the effect of linseed oil (LO) replacing different levels of fish oil (FO) on growth, muscle fatty acid composition and metabolism of gift tilapia (Oreochromis niloticus) (mean initial weight 22 ± 0.5 g) in indoor recycle aquarium tanks for 8 weeks. Fish fed the diet with 50% of the oil as LO had higher final body weight (FWG), specific growth rate (SGR) and protein efficiency ratio (PER) than the other groups (P < 0.05). Hepatopancreas lipid content of fish fed 50% LO was lower than the other groups. Total n‐3 and n‐6 PUFA contents in the dorsal muscle and superoxide dismutase (SOD) activity in serum increased with increasing dietary LO level. Fish fed 50% LO had higher alanine transaminase (ALT), aspartate transaminase (AST) and lipoprotein lipase (LPL) activities in hepatopancreas and total antioxidant capacity (T‐AOC) and alkaline phosphatase (AKP) activities in serum than the other groups (P < 0.05). However, malate dehydrogenase (MDH) activities and malondialdehyde (MDA) contents in hepatopancreas were lower than other groups (P < 0.05) with a 50% substitution level. Results of this study indicated that LO could substitute <50% FO without influencing the growth of tilapia. The higher substitution levels of LO induced negative influences on growth, feed utilization and antioxidant ability of tilapia, but could promote DHA synthesis in tilapia muscle.     

Potential of local agricultural by-products for the rearing of African catfish Clarias gariepinus in Rwanda: effects on growth, feed utilization and body composition

This study was performed to evaluate the effect of replacing fish meal with local by‐products on Clarias gariepinus growth performance, feed utilization and body composition. A control diet contained 50% of fish meal. In four other diets, fish meal was partially replaced by vegetable and animal protein blend composed of sunflower oil cake, soybean oil cake, groundnut oil cake, bean meal, chicken viscera and blood meal. The study was conducted in a recirculating water system at a mean temperature of 23.6°C. The five test diets were compared with a commercial diet developed for African catfish. All diets were balanced to be equal in gross energy (19 kJ g⁻¹) and crude protein (40%). The experimental groups were fed in triplicate for 8 weeks, increasing fish weight from about 6.2 g at start to 52.3 g in the end. Best specific growth rate (SGR=3.4), feed efficiency (FE=1.3) and protein efficiency ratio (PER=3) were obtained with the control diet (diet 50% fish meal), although there were no significant differences between the group of fish fed the control diet and those fed diets based on groundnut oil cake or bean meal, whereas SGR (2.17), FE (0.85) and PER (1.95) were significantly (P<0.01) lower in fish fed diet containing sunflower oil cake. No significant differences (P<0.05) were found in fish fed commercial diet and diets containing bean meal or groundnut oil cake. Groundnut oil cake or bean meal can thus replace at least 50% of fish meal in the diet of Clarias fingerlings without amino acid supplementation. Because of its economic importance and its potential in animal nutrition sunflower oil cake is still an interesting feed ingredient, but its efficiency should be improved by various processing techniques. African catfish can utilize efficiently a diet with low percentage of animal protein without growth reduction.     

Effects of dietary sunflower oil on growth parameters,fatty acid profiles and expression of genes regulating growth and metabolism in the pejerrey (Odontesthes bonariensis) fry

Aquaculture fish diets usually contain an addition of fish oil to improve their nutritional value. The effect of the replacement of dietary fish oil (FO) by sunflower oil (SfO) on growth, fatty acid composition and expression of genes implicated in somatic growth, feed intake and fatty acid metabolism was studied in pejerrey fry. Fry were fed per 45 days with diets containing FO/SfO ratios of 100% FO; 50% FO:50% SfO; 20% FO:80% SfO; and 100% SfO. No differences were detected in growth and in the total per cent of saturated and monounsaturated fatty acids. Gh, ghr‐I and ghr‐II showed a higher mRNA expression in head and trunk of fry fed with 100% SfO diet. Expression of igf‐II was higher in trunk of fry fed with 100% SfO diet compared with 100% FO diet. The Δ6‐desaturase gene expression was upregulated in head and trunk of fry fed with 100% SfO diet. The nucb2/nesfatin‐1 gene expression decreased in the trunk of fry with increasing dietary SfO. We conclude that the replacement of fish oil by sunflower oil in pejerrey fry feed does not affect growth and is a viable strategy to reduce production costs of this fish.     

Effect of Dietary Safflower and Canola Oil on Growth Performance,Body, and Fatty Acid Composition of Rainbow Trout (Oncorhynchus mykiss)

The objective of the present study was to evaluate the effects of the diets enriched with safflower and canola oil on growth, feed utilization, body composition, liver, and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss). Rainbow trout having approximate initial weight of 97.03 ± 0.10 g were fed the experimental diets containing only fish oil (Group 0SFO), safflower oil (50% safflower oil, Group 50SFO and 33% safflower oil, Group 33SFO), and vegetable oil blend (33% safflower and 33% canola oil, Group 66SFCO) for 45 days. Twenty-five fish were randomly assigned for triplicate treatments and offered the test diets two times daily to apparent satiation. At the end of the experiment, survival was 100% in all treatments. No significant differences in the weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio were found between fish fed with the different experimental diets. The highest hepatosomatic index (HIS) and viscerasomatic index (VSI) was obtained in 50SFO and 33SFO groups, respectively. The moisture, protein, lipid, and ash content in the body composition of the fish increased in all experimental groups. The lipid content was not significantly different among the groups (p > 0.05); however, there was a significant difference in ash content between the control and the other groups (p < 0.05). The experimental diets containing vegetable oil (50SFO and 33SFO groups) and vegetable oil blend (66SFCO group) had significantly higher concentrations of n-6 fatty acids, predominantly in the form of linoleic acid (LA). The n-3 fatty acids were present in significantly higher concentration in the control treatment (0SFO). The fatty acid composition of fish fillet and liver were reflective of the dietary lipid source. While the fillet and liver of fish fed the 50SFO diet was high in linoleic acid (18:2 n-6), fish fed the 66SFCO diet had high concentrations of oleic acid (OA; 18:1 n-9). The present study suggests that fish oil can be replaced by up to 50% with safflower oil and by up to 66% with safflower + canola oil blend in rainbow trout diets with no significant effect on growth.