Vegetable oil blend as alternative lipid resources in diets for gilthead seabream, Sparus aurata

The recent decreasing worldwide supplies of marine oils have forced the aquaculture industry to investigate alternative lipid sources for use in marine fish feeds. The aim of this study was to determine the impact of dietary replacement of fish oil by vegetable oils on gilthead seabream (Sparus aurata) growth performance, nutritive utilization, body composition, and fatty acid profile as well as feed cost. Two dietary vegetable oil (VO) mix blends (VO1 and VO2) in which: sunflower (SO), cottonseed (CO) and linseed (LO) for VO1 or soybean oil (SBO) for VO2, were tested as 60% fish oil (FO) substitutes versus the 100% FO control or reference diet (FO). Three iso-proteic (46% CP) and iso-lipidic (18%) experimental diets were hand fed, twice a day, 6 days a week to apparent visual satiety to triplicate groups of seabream growers (average initial weight, 130.9 ± 3.44 g), until fish reached market size (300–400 g/fish) after 20 weeks at mean ambient temperature 27.0 ± 1.8°C. All experimental diets were well accepted by seabream growers regardless of the different lipid sources used, as overall mean feed intake (FI) and daily intake (DFI) were not significantly different (P > 0.05) among dietary treatments. In terms of growth performance, fish fed VO1 diet (with LO) exhibited a relatively lower, but significant (P < 0.05), total weight gain (WG) than fish fed all FO diet (FO). However, mean value of WG of fish fed either vegetable oil-tested diet was nonsignificantly different. Feeding seabream growers vegetable oil (VO) diets (VO1 or VO2) had no significant effect on specific growth rate (SGR), daily weight index (DWI), or feed conversion ratio (FCR) among dietary treatments. Consumption of VO for 20 weeks did not significantly alter the major nutrient composition of fish, but the muscle fatty acid (FA) profile was significantly altered compared to the reference FO diet. Comparatively reduced levels of eicosapentaenoic acid (EPA) and docosahexaenoic acids (DHA), as well as elevated levels of linoleic and linolenic acids (LA and LNA) compared with fish fed the FO were noticed. In terms of economics, 17 or 20% reduction in Kg feed cost was obtained for diets VO1 or VO2, respectively. In terms of growth performance and cost, VO2 diet showed slight relative superiority over VO1 diet. However, in terms of liver structure morphology, VO1 diet (with LO) has resulted in less fat-infiltration and altered hepatic cells than VO2 (with SBO). As these traits do not affect yield or the price paid for the fish, VO2 diet has therefore been considered better than VO1 as complementary lipid sources for gilthead seabream grower diets.     

Growth and immune response of Chinese mitten crab (Eriocheir sinensis) fed diets containing different lipid sources

A 10‐week feeding trial was conducted to evaluate the effects of dietary lipid sources on the growth and immune responses of Chinese mitten crab Eriocheir sinensis. Six isonitrogenous and isoenergetic diets were formulated with fish oil (FO), linseed oil (LO), soybean oil (SO), rapeseed oil (RO), coconut oil (CO) and beef tallow (BT) as the sources of lipid with five replicates each. Thirty crabs (2.35 ± 0.14 g) were stocked into each tank and fed twice daily. Weight gain and specific growth rate of crab fed the FO diet were significantly lower than those fed other diets (P < 0.05), except for crabs fed LO diet (P < 0.05). Crab fed the SO diet weighed more than those fed FO diets (P < 0.05). Serum superoxide dismutase and malondialdehyde of crab fed the FO diet were significantly higher than in other groups (P < 0.05). Crab fed the FO diet had the highest activities of serum phenoloxidase, acid phosphatase, alkaline phosphatase and lysozyme (P < 0.05). The fatty acid composition in the liver of crab reflected the change in test diets. Our results indicate that the use of dietary vegetable or animal oils can achieve similar growth performance to the use of dietary FO in Chinese mitten crab, but non‐FOs may impair crab immunity. Soybean oil is recommended as a suitable replacer for FO in Chinese mitten crab diet.     

Influence of Dietary Oil Sources on Muscle Composition and Plasma Lipoprotein Concentrations in Nile Tilapia,Oreochromis niloticus

To investigate the impact of different dietary lipid sources on fillet composition and lipid transport, we conducted a feeding trial and evaluated the proximate composition of muscle tissue, fatty acid profiles, total cholesterol (in muscle and plasma), triglycerides, and lipoprotein concentrations in Nile tilapia, Oreochromis niloticus. Five semi‐purified diets, containing different oils (soybean – SO, corn – CO, linseed – LO, fish – FO, and olive – OO), were supplied to tilapia for 160 d. Fish fed with LO and FO diets had a lower percentage of total lipids in muscle compared with the others (P < 0.05). The highest percentage of protein was found in fish fed with FO diet (P < 0.05). The muscle fatty acid profile was influenced differently by diets (P < 0.05). The group supplemented with SO and CO had a higher concentration of 18:2n‐6, whereas the fish fed with LO diet had a higher level of 18:3n‐3 and those that received the FO diet had more 22:6n‐3 in comparison with those supplemented with vegetable oils. Plasma lipid transport was also affected by the diets: the fish fed with FO diet had higher total cholesterol and high‐density lipoprotein and lower very‐low‐density lipoprotein concentrations (P < 0.05).     

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 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.     

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

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

Combined effects of dietary mannan oligosaccharides and total fish oil substitution by soybean oil on European sea bass (Dicentrarchus labrax) juvenile diets

This study evaluates the effects of dietary mannan oligosaccharides (MOS) on growth, tissue composition, fatty acid profiles and liver morphology of European sea bass (Dicentrarchus labrax) fed diets containing either soybean oil (SBO; SBOMOS) or fish oil (FO; FOMOS) as unique oil source for 8 weeks. Results showed that MOS supplementation enhanced specific growth rate, regardless of the oil source used, and that dietary oil source reduced fish length, regardless of dietary MOS supplementation. Dietary MOS favoured lipid accumulation in muscle and anterior intestine when supplemented in FO‐based diets compared to fish fed SBO diet and reduces it in liver in relation to lower hepatocyte area, particularly in fish fed SBOMOS diet. Dietary MOS favoured liver and not muscular ∑n‐3 PUFA, DHA, EPA and ARA deposition, when combined with FO but not when included in SBO‐based diets. Thus, MOS dietary supplementation favours fish performance and helps to minimize the side effects derived from high dietary SBO supplementation on liver lipid accumulation and hepatocyte vacuolization, which could be of especial interest on long‐term feeding trials; however, the effects on favoured deposition ∑n‐3 PUFA are limited to FO‐based diets.     

Effects of alternative dietary lipid sources on growth performance,health status and fillet fatty acid composition of hybrid sturgeon (Acipenser baeri Brandt ♀ × Acipenser schrenckii Brandt ♂)

An 8‐week trial was conducted to determine the effects of total replacement of 12.9% fish oil (FO) with soybean oil (SBO), peanut oil (PNO), sunflower seed oil (SFSO), corn oil (CO) and canola oil (CNO) on growth performance, health status and fillet fatty acid composition of hybrid sturgeon (194.28 ± 0.14 g). Compared to the FO group, dietary SBO decreased growth performance (p < .05), increased serum glucose and hepatic lipid content (p < .05). No obvious adverse effects on growth performance and health status were observed in PNO, SFSO and CO groups (p > 0.05). The fish fed with CNO had increased growth performance (p < .05), reduced serum ALT, AST, LDL‐C (p < .05) and enhanced serum GSH‐Px, T‐AOC, and LZM, MPO, C4 (p < .05). The contents of C18:1n9, C18:2n6, and ∑n‐3 PUFA and ∑n‐6 PUFA in fillets showed a positive linear correlation with the diets (p < .05). In summary, PNO, SFSO and CO are probable alternative lipid sources to fully replace FO. Hybrid sturgeon prefers to use CNO as a lipid source with improved growth performance and health status. The fillet fatty acid composition mirrors the dietary fatty acid composition.     

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.     

Effects of different dietary lipid sources in the diet for Pangasius hypophthalmus (Sauvage, 1878) juvenile on growth performance,nutrient utilization,body indices and muscle and liver fatty acid composition

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 lipid sources each at inclusion level of 120 g kg^?1 and fed to triplicate groups of 15 juvenile iridescent shark, Pangasius hypophthalmus (Sauvage, 1878) (mean weight 10.00 ± 0.70 g) to apparent satiation twice daily for 12 weeks. The results showed that survival of fish was consistently over 95% for all treatments whereas growth performance in the SBO and CPO treatments was similar and significantly (P < 0.05) higher than for fish fed the LO diet. However, fish fed all vegetable oil‐based diets performed better than those fed the FO diet. Muscle and liver fatty acid composition for all treatments generally reflected the composition in the diet and the ratio of n‐3/n‐6 was found to play an important role in P. hypophthalmus, suggesting that excessive amounts of n‐3 fatty acids reduce the overall growth performance. Results of this study thus suggests that P. hypophthalmus fed diets containing vegetable oils (especially CPO and SBO) produce better growth than those fed FO diet without showing any signs of nutrient deficiency.     

Effects of dietary fish oil and soya bean lecithin on gonad index,colour and biochemical composition of the purple sea urchin,Strongylocentrotus purpuratus (Stimpson 1857)

The effects of increasing soya bean lecithin (SL) levels (0%, 2% and 4% of diet dry matter, DM) at two fish oil (FO) levels (0% and 3% DM) on gonad index, colour and biochemical composition of Strongylocentrotus purpuratus were evaluated using a 3 × 2 factorial design with six iso‐nitrogenous formulated diets. All diets generated an increase in gonad index of more than 9%. Dietary FO had a positive effect on diet digestibility and accumulation of proteins in the gonad. Soy lecithin did not affect gonad composition, but improved its coloration, decreased gonad feed conversion ratio and increased gonad protein efficiency. There was a clear effect of diets on sea urchins gonad protein, ash and fatty acid content, in particular, decreasing the n‐3/n‐6 ratio associated with a decrease in 20:5n‐3 when SL levels increased. Nevertheless, 22:6n‐3 levels increased by week 12 in all treatments, and diets with SL increased the content of 20:4n‐6 in gonads. A decrease in bitter‐tasting amino acids such as histidine, cysteine, valine and methionine was observed in all treatments with a concomitant increase in isoleucine levels. We recommend using a diet containing 3% of FO and 2% of SL to increase food consumption, diet digestibility, improving marketable gonad colour and an increasing gonad n‐6 fatty acids and C22:6n‐3. In addition, the present study paves the way for future research in the use of FO and SL as an additive in diets for S. purpuratus towards the goal of increasing gonad size and nutritional quality.     

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 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.     

Effects of different dietary lipids on growth,body composition and lipid metabolism‐related enzymes and genes in juvenile largemouth bass,Micropterus salmoides

This study investigates the effects of different lipids on growth, body composition and lipid metabolism of largemouth sea bass fish Micropterus salmoides. A total of 360 juvenile M. salmoides (mean ± SD mass = 33.83 ± 0.15 g) were randomly stocked into 12 tanks of 0.5 m³ volume for 8 weeks. Four replicates were made in each group, which were fed one of three diets containing fish oil (FO), soybean oil (SO) or lard oil (LO). The weight gain rate and specific growth rate did not differ among the groups (p > 0.05). Fish oil fish had the lowest condition factor (p < 0.05) and highest serum glucose content (p < 0.05). Crude lipid contents in the whole body and in the liver and muscle of FO fish were significantly lower than in the SO and LO groups (p < 0.05). The fatty acid composition of whole‐body lipids was closely correlated with that of the diet. The carnitine palmitoyltransferase 1 (cpt1) activity in the FO group was significantly higher than those in the SO and LO groups (p < 0.05). No significant differences in fatty acid synthase (fasn) activity were observed among the groups (p > 0.05). The Cpt1 and fasn gene expression levels in the FO group were significantly higher than those of the SO and LO groups (p < 0.05). The apolipoprotein B100 gene expression level was significantly higher in the SO group than in the FO group (p < 0.05). Fatty acid‐binding protein 1 gene expression levels in the FO and SO groups were not different (p > 0.05) but were both higher than that of the LO group (p < 0.05). The delta‐6 fatty acyl desaturase gene expression level in the LO group was significantly higher than that in the FO group (p < 0.05), but lower than that in the SO group (p < 0.05). It can be concluded that FO can be completely replaced by SO or LO in the M. salmoides diet, at least within the 8‐week culture period. Different types of dietary lipids significantly affect body condition and hepatic lipid metabolism in M. salmoides.     

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

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

Replacement of fish oil with soybean oil in diets for juvenile Chinese sucker (<Emphasis Type="Italic">Myxocyprinus asiaticus</Emphasis>): effects on liver lipid peroxidation and biochemical composition

This study was designed to evaluate the effect of the replacement of fish oil (FO) by soybean oil (SO) on growth performance, liver lipid peroxidation, and biochemical composition in juvenile Chinese sucker, Myxocyprinus asiaticus. Fish (13.7 ± 0.2 g) in triplicate were fed five experimental diets in which 0% (FO as control), 40% (SO40), 60% (SO60), 80% (SO40), and 100% (SO100) FO were replaced by SO. The body weight gain of fish fed SO40, SO60, or SO80 diet was similar to FO group, but diets that have 100% soybean oil as dietary lipid significantly reduced fish growth (P < 0.05). Although the level of SO resulted in increasing crude lipid content of the liver, the level of SO did not significantly alter the hepatosomatic index (HSI). Indicators of peroxidation, such as vitamin E (V_E) and thiobarbituric acid-reactive substance (TBARS) contents, were changed as increasing dietary SO. It was shown that the inclusion of SO in the diets increased V_E concentrations, but reduced TBARS in the liver and total cholesterol (T-CHO) in the plasma. Linoleic acid (LA) and linolenic acid (LNA) significantly increased in fish liver fed diets that contained SO, but eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and the ratio n-3/n-6 were significantly reduced by the inclusion of dietary SO (P < 0.05). Our results indicated that the inclusion of SO increased the hepatic V_E content and reduced lipid peroxidation in fish. However, diet containing 100% SO as dietary lipid could reduce growth performance. Thus, we recommended that 40–80% SO can be used as dietary lipid to replace FO for juvenile Chinese sucker.     

Cottonseed oil as a complementary lipid source in diets for gilthead seabream Sparus aurata juveniles

The efficacy of using cottonseed oil (CSO) as a fish oil (FO) substitute in gilthead seabream (Sparus aurata) juveniles feed was evaluated. Fish (BW_i 4.0 ± 2.9 g) were fed one of four isoproteic (~48% CP) and isolipidic (~18% L) diets for 9 weeks. Added oil was either FO (control diet, CTRL) or CSO, replacing 50% (CSO50 diet), 60% (CSO60 diet) and 70% (CSO70 diet) of dietary FO. Results indicated that FO replacement by CSO up to 60% level had no detrimental effects on growth or nutritive utilization and composition in fish muscles. Higher CSO intake (CSO70 diet, 56 g kg^?1) led to a 16% reduction in weight gain, 14% in feed utilization (FCR) and 57% in muscle n‐3 long‐chain polyunsaturated fatty acids (lc PUFA) as compared with CTRL and to abundant accumulation of lipid within the hepatocytes. Use of CSO altered fatty acid (FA) profiles of muscle and liver. Data suggested utilization of linoleic acid (LOA) by fish and retain of docosahexaenoic acid (DHA) in muscles. Therefore, limits of CSO inclusion as the main source of supplementary dietary lipid, with no negative effects on fish performance or nutritive composition and utilization in muscles, are: 40–48 g kg^?1 feed for gilthead seabream juveniles.     

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

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