Complete Replacement Of Fish Oil Research Articles

Effects of micro‐algae dietary oil replacement on growth, omega − 3 deposition and gut microbiome composition of Nile tilapia (Oreochromis niloticus)

AbstractMicroalgae offer a sustainable source of omega − 3 fatty acids that can replace fish oil in aquafeeds, but the nutritional benefits are not always clear, particularly when microalgae are used as complete oil replacements in starter feeds. We compared the survival, growth, omega − 3 deposition and composition of the gut microbiota of juvenile mixed‐sex Nile tilapia (Oreochromis niloticus) that had been fed over a 3‐month period on six isonitrogenous, isolipidic and isocaloric aquafeeds that varied only on the contribution of fish oil, soya oil and microalgae (Schizochytrium) oil as lipid sources. Survival was not affected by diet, but fish fed a diet where the entire oil component (5%) was replaced by microalgae oil grew twice as fast as fish fed plant oil or a mixture of plant and fish oil. Dietary omega − 3 content was strongly correlated with omega − 3 deposition in the fish fillet. Complete replacement of fish oil by plant oil caused a significant decrease in the abundance of Peptostreptococcaceae and an increase in the abundance of Aeromonadaceae which is often associated with an inflammatory response in the fish gut. In contrast, when fish and soya oil in the reference diet were replaced by 100% microalgae oil, an increase in Mycobacteriaceae was observed. Our study indicates that Schizochytrium oil can be used to improve the growth of Nile tilapia and increase its omega − 3 content without any of the detrimental effects on the gut microbiome typically associated with some plant oil replacements.

Effects of replacement of dietary fish oil with plant oil on growth performance and fatty acid composition of spinefoot rabbitfish, Siganus rivulatus.

A 95-day feeding study was carried out to evaluate the impact of complete replacement of fish oil by plant oils in the growth performance, feed consumption fatty acid and body composition of juvenile rabbitfish, Siganus rivulatus. There were four treatments i.e., A (fish oil diet), (linseed oil diet), C (soybean meal oil diet) and D (sunflower oil diet). The experimental trial was conducted in twelve 1.5-m3 fiber glass tanks (n=3). Spinefoot rabbitfish juveniles had an average initial weight of 0.948 g ± 0.124 g and they were stocked at 50 fish per tank. Fish fed diet A showed significantly better growth rate, final body weight, and total body weight than fish fed on the other diets. Moreover, the best FCR was observed for diet A followed by diet C and diets B and D had the worst FCR. Fish body composition for crude protein, dry matter, ashes and gross energy at the end of the trial had not differed between the treatments. The highest polyunsaturated fatty acids (PUFA) was found in fish fed diet A followed in decreasing order by diets D, B, and C. Fish oil is a better dietary lipid source for Spinefoot rabbitfish juveniles, Siganus rivulatus, than plant oils. Among plant oils, soybean oil was better than linseed oil and sunflower oil as the main dietary fat source.

Effects of Different Marine-Based Lipid Sources on Growth Performance, Activities of Digestive Enzyme, Antioxidant Responses, and Lipid Metabolism of Large Yellow Croaker (Larimichthys crocea) Larvae

The study of lipid nutrition is an important guarantee for the development of high-efficiency artificial microdiet for fish larvae. Existing studies on lipid nutrition of larvae mainly focus on nutrient requirements and metabolism through a single lipid source. However, there are few reports on the effects of different marine-based lipid sources on fish larvae. In this study, a 30-day feeding experiment was conducted to evaluate the effects of different dietary marine-based lipid sources on survival, growth performance, appetite gene expression, activities of digestive enzyme, antioxidant responses, and lipid metabolism of large yellow croaker (Larimichthys crocea) larvae (initial weight 4.71 ± 0.21 mg ). Four isonitrogenous (520 g/kg crude protein) and isolipidic (190 g/kg crude lipid) diets were formulated to contain fish oil (FO), krill oil (KO), squid viscera oil (SVO), and Schizochytrium sp. oil (SSO), respectively. Results showed that larvae fed with the SSO diet had significantly higher survival rate (SR) than those fed with dietary FO and SVO ( P < 0.05 ). However, larvae fed with the SSO diet had significantly lower final body weight (FBW) and specific growth rate (SGR) than those fed with other diets ( P < 0.05 ). Furthermore, larvae fed with the SSO diet had significantly higher percentage of total n-3 long-chain polyunsaturated fatty acids (LC-PUFA) than those fed with other diets, followed by KO and SVO diets ( P < 0.05 ). Larvae fed with the SSO diet had significantly lower mRNA expression of orexigenic genes (npy and ghrelin) and significantly higher mRNA expression of anorexigenic gene (cart) than those fed with dietary FO ( P < 0.05 ). Meanwhile, larvae fed with the SSO diet had significantly higher activity of alkaline phosphatase (AKP) in intestinal segments (IS) and brush border membrane (BBM) than those fed with dietary FO and SVO ( P < 0.05 ). Larvae fed with the SSO diet had significantly higher activity of total antioxidant capacity (T-AOC) than those fed with dietary FO ( P < 0.05 ). The TG content and mRNA expression of lipogenesis genes (srebp-1c, fas, and scd1) were markedly lower in larvae fed with SSO, KO, and SVO diets than in those fed with dietary FO ( P < 0.05 ). Meanwhile, larvae fed with KO and SSO diets had significantly higher mRNA expression of the lipolysis gene (cpt-1) than those fed with other diets ( P < 0.05 ). In conclusion, results of the present study showed that FO can be completely replaced in large yellow croaker larvae feed with KO and SVO without negative effects. Moreover, the complete replacement of FO by SSO can improve survival, activities of digestive enzyme, antioxidant responses, and lipid metabolism, despite inhibiting the appetite and growth of large yellow croaker larvae.

Complete replacement of fish oil by three microalgal products rich in n-3 long-chain polyunsaturated fatty acids in early weaning microdiets for gilthead sea bream (Sparus aurata)

The aim of the present study was to evaluate the effect of different n-3 LC-PUFA-rich microalgae replacing FO in larval diets, on performance, biochemical composition and health of gilthead sea bream (Sparus aurata). Dietary fish oil (FO) was replaced with oleic acid (OA) or 3 n-3 LC-PUFA-rich algae products (2 commercial products: All G Rich and DHA Gold, and a development product: MO060). The five early weaning microdiets were fed to 20-dah gilthead sea bream larvae for 21 days. Proximate composition and fatty acid profiles of total, neutral and polar lipids of seabream larvae were analysed, as well as hepatocyte morphology and the expression of selected genes related to lipid metabolism. OA diet significantly inhibited larval growth and survival after a stress challenge, whereas FO replacement by DHA Gold and MO60 led to a higher body weight, total length, and stress resistance. Larvae fed the diets containing microalgae had increased DHA content in whole body lipids and showed a down-regulation of expression of fads2, indicating an inhibition of LC-PUFA biosynthesis. Relative expression of genes related to lipid (ppar-α) or eicosanoids (cox-2 and 5-lox) metabolism were unaffected by the replacement of FO by any of the three microalgal products or OA. In conclusion, all the microalgae products tested were effective total replacers of FO in weaning microdiets for gilthead sea bream larvae, providing the necessary dietary n-3 LC-PUFA for optimal growth and survival.

Effects of dietary linolenic acid to linoleic acid ratio on growth performance, proximate composition and fatty acid contents of pacu ( Piaractus mesopotamicus )

Freshwater fish have the ability to convert linolenic acid (LNA) into EPA and DHA and linoleic acid (LA) into ARA from elongation and desaturation process. The optimal LNA/LA in aquafeeds formulated with vegetable oils can improve the n-3/n-6 ratio in fish flesh. This study aimed at determining the effects of varying dietary LNA/LA ratios on the growth and proximate composition and fatty acids content in the flesh of pacu, Piaractus mesopotamicus. Juvenile pacu (110 ± 1.6 g) were fed for 60 days with diets containing varying levels of sunflower (SO) and linseed (LO) oils (100SO; 75SO:25LO; 50SO:50LO; 25SO:75LO; 100LO), and performance and proximate composition and fatty acids contents of fish flesh were analysed. Experimental diets did not affect fish growth performance. Although the EPA and DHA content were lower in the fish fed the experimental diets than control diet (fish oil), the complete replacement of fish oil by an approximate proportion of 12SO:88LO, in an optimal LNA/LA ratio (2.2–2.4), represents an improvement in nutraceutical quality of the flesh for human consumption. Fish-fed ideal LNA/LA ratio diets have higher total n-3 fatty acids contents, and higher n-3/n-6 and EPA/ARA ratios, without hampering fish performance and flesh proximate composition.

Plant Ingredient diet supplemented with lecithin as fish meal and fish oil alternative affects growth performance, serum biochemical, lipid metabolism and growth‐related gene expression in Nile tilapia

The current study evaluated the effects of replacing fish meal (FM) and fish oil (FO) with plant ingredients without or with lecithin supplementation on Nile tilapia growth, blood biochemistry, intestinal morphology, growth- and lipid-metabolism-related gene expression. Fingerlings were assigned to six dietary groups: FM and FO (G1), FM and plant oil (G2), plant protein and plant oil (G3), and the same three treatments but with lecithin supplementation (G4–G6) respectively. Fingerlings in G1 and G2 showed higher body weight than fish in G3 (p > 0.05). Lecithin supplementation improved (p < 0.05) growth, particularly in fish fed plant ingredients (G6). Fish fed different diets showed a significant increase (p < 0.05) in serum total cholesterol and low-density lipoprotein concentrations compared with G1. Albumin concentration was significantly reduced in G3 and G6. Partial or complete replacement of FO and FM with plant ingredients, with or without lecithin, significantly modulated (p < 0.05) expression levels of some regulatory genes related to growth and lipid metabolism, with the highest expression in lecithin-supplemented fish. It could be concluded that the complete replacement of FM and FO with plant ingredients (plant protein and oil) non-significantly reduced fish performance. Nevertheless, with lecithin supplementation, Nile tilapia can effectively utilize this plant-based diet as reflected with enhanced growth.

Complete replacement of fish oil and fish meal in the diet of juvenile California yellowtail Seriola dorsalis

California yellowtail (CYT) Seriola dorsalis is a top candidate for aquaculture in southern California. CYT is fed commercial diets whose nutrient profile and ingredient composition rely heavily on fish meal and fish oil. We evaluated the complete replacement of fish oil and fish meal with a Schizochytrium-derived algal oil as an essential fatty acid source and poultry by-product meal and spirulina as primary protein sources, in the diet of juvenile CYT (average initial weight—19.95 ± 0.09 g). The treatment diets for this study included the following: FMF-FO—fish meal free, fish oil; FMF-AO—fish meal free, algal oil; FMF-SO—fish meal free, soybean oil; FMC-FO—fish meal control, fish oil. Each treatment diet was formulated to contain 45% protein and 15% lipid, and the trial lasted 64 days. At the conclusion of the trial, fish from FMC-FO group had performed significantly better in three key performance metrics: final body weight of 185.96 ± 8.98 g, per cent weight gain of 832.7 ± 47.2% and lowest FCR of 1.16 ± 0.04. Replacing fish meal with poultry by-product meal and spirulina resulted in 20% less weight gain. Replacing fish oil with algal oil, in a fish meal free diet, resulted in equal weight gain, and the fish had higher tissue essential fatty acid content. Based on the results from this trial, we have shown that in CYT juvenile diets, fish oil can be replaced with algal oil with no effect on growth or survival and fish meal can be replaced with no effect on survival and a 20% decrease in weight gain.

Replacement of dietary fish oil with plant oils improves the immunological responses and the antioxidant status in Oreochromis niloticus exposed to suboptimal temperature.

Here, we investigated the effects of total dietary fish oil (FO) substitution with plant oil (PO) on hematological indices, immune status, antioxidant activity, IL1β and TNF-α gene expression, and hypoxia stress resistance in Oreochromis niloticus at suboptimal temperatures. Fish (n = 360) were randomly divided into 12 circular fiberglass tanks (500L; 3 replicates for each dietary group, 30 fish/replicate, 90 fish/group). The control group was fed a basal diet with FO as the lipid source. The CO, SFO, and LSO groups were fed a basal diet with complete replacement of FO with corn, sunflower, and linseed oils, respectively. After 4weeks, no effects on hematological indices were observed in fish fed the experimental diets. The LSO and CO groups showed a significant increase in γ globulin levels. The highest levels of non-specific immune parameters, antioxidant activity, and IL-1β and TNF-α gene expressions were recorded in the LSO group. The LSO group also exhibited good resistance to hypoxia stress. Therefore, the total dietary substitution of FO with PO (especially LSO and CO) is recommended as a valuable strategy to ameliorate the immunosuppressive effects of suboptimal temperatures and enhance the resistance of O. niloticus to hypoxia stress.

Effective complete replacement of fish oil by combining poultry and microalgae oils in practical diets for gilthead sea bream (Sparus aurata) fingerlings

Few ingredients allow the complete replacement of fish meals (FM) and fish oils (FO) in aquaculture feeds without affecting fish performance or fillet nutritive value. This is due to the adequate content of essential nutrients, including the n-3 long-chain polyunsaturated fatty acids (n-3 LC PUFA), and the unique high palatability of FM and fish oil. Some microalgae present abundant amounts of these fatty acids, for instance docosahexaenoic acid (DHA). Therefore, the aim of the present study was to evaluate the effect of two different microalgae products, one providing DHA and eicosapentaenoic acid (EPA, 20:5n-3; ED diet), and the other one DHA and n-6 docosapentaenoic acid (DPA, 22:5n-6; DD diet), in combination with poultry oil and rapeseed oil, as total replacers of fish oil, at two different dietary fish meal contents (15 and 7.5%). The effects of these dietary oil combinations on performance, composition and nutritive quality indexes of gilthead sea bream (Sparus aurata) juveniles were studied and compared against a positive control diet (FO) and two negative control diets (PO diets), one for each dietary fish meal content tested, giving in total 7 experimental diets. Both microalgae products in combination with poultry and rapseed oils were able to completely replace fish oil in practical diets with 15% FM without affecting growth performance, utilization of dietary fatty acids or the nutritional quality of fish fillet for the consumer. On the contrary, PO alone was not able to completely replace fish oil and negatively affected fish performance, in relation to an insufficient dietary n-3 LC-PUFA content. A similar decrease in growth performance was also observed with the reduction of the dietary FM content to 7.5%. In conclusion, both oils from microalgae, providing either DHA and EPA or DHA and n-6 DPA, were effective n-3 LC-PUFA sources for sea bream juveniles and allowed complete replacement of fish oil in combination with more cost-effective lipid sources, such as poultry and rapeseed oils.

Effects of complete replacement of fish oil with plant oil mixtures and algal meal on growth performance and fatty acid composition in juvenile yellowtail Seriola quinqueradiata

Docosahexaenoic acid (DHA) is an essential fatty acid for marine carnivorous fish. Algal meal (AM), available as a new dietary DHA source, could completely replace dietary fish oil (FO). In this study, dietary FO was replaced with plant oil mixtures and AM in juvenile yellowtail Seriola quinqueradiata to investigate its effects on growth performance and fatty acid composition. The FO control diet was prepared with only pollack liver oil as the lipid source. For the non-FO diets, pollack liver oil was completely replaced with mixtures of canola oil and palm oil, with AM supplementation at 0% (AM0), 1% (AM1), 2% (AM2), 3% (AM3), and 4% (AM4). After completion of the 8-week feeding trial, the AM2 group showed significantly higher values for final body weight and feed efficiency than the AM0 group. No significant differences were observed in the other parameters of growth performance. Whole-body fatty acid composition reflected the dietary fatty acid composition in all dietary groups. These findings demonstrate that AM is useful as a DHA source in yellowtail aquaculture, thus contributing to a reduction in the use of FO in fish diets.

Total replacement of dietary fish oil with alternative lipid sources in a practical diet for mandarin fish, Siniperca scherzeri, juveniles

A 12-week feeding trial was designed to evaluate the effect of total replacement of fish oil (FO) with terrestrial alternative oils on growth, feed utilization, body composition, hematological parameters, and fillet fatty acid profile of mandarin fish juveniles. Four iso-nitrogenous (56% crude protein) and iso-lipidic (13% crude lipid) practical diets were formulated. A control diet contained 6% FO and three other experimental diets were prepared by replacing FO with linseed oil, soybean oil, and lard (designed as FO, LO, SO, and lard, respectively). Each diet was randomly allocated to triplicate groups of 25 fish (1.8 ± 0.03 g/fish) in a circular tank. Complete replacement of FO by three tested alternative oils had no remarkable impact on growth performance, feed utilization efficiency, and morphological and hematological parameters of juvenile mandarin fish. However, daily feed intake was found to be significantly higher for fish fed the SO diet compared with those fed the FO and LO diets. Fish fed LO and SO diets exhibited significantly higher levels of the whole body lipid compared to fish fed diet containing FO. Fillet fatty acid composition reflected dietary fatty acid profile. The highest level of α-linolenic acid, linoleic acid, and oleic acid was observed in fish fillet fed LO, SO, and lard, respectively. Although the eicosapentaenoic acid level of fish fillet fed diet FO was higher than other treatments, no significant difference was found in docosahexaenoic acid content among all dietary groups. The results of the present study clearly demonstrate that the complete replacement of FO in mandarin fish diets is achievable. These findings are useful in dietary formulation to reduce feed costs without compromising mandarin fish growth.

Tropical Vegetable Oils Do Not Alter Growth Performance in African Catfish through a High n‐6 Polyunsaturated Fatty Acids Biosynthesis Capacity

The main objective of this study was to determine the best vegetable oils (VO) for nutrition of African catfish by assessing the effects of a complete replacement of fish oil (FO) by different VO sources on its growth performance, fatty acid composition, and elongase-desaturase gene expression levels. Fish (16.2 g of initial body weight) were fed with five experimental isonitrogenous, isolipidic, and isoenergetic diets in which FO was totally replaced by cottonseed oil (CO), palm oil (PO), desert date oil (DO), or Shea butter (SB). Complete replacement of FO with VO did not affect growth performance except for low values in fish fed SB diet. Muscle n-3 LC-polyunsaturated fatty acids (PUFA) were significantly reduced in fish fed VO-based diets when compared with FO fed fish. However, the muscle arachidinic acid (ARA) levels in phospholipid class were 1.4 to 1.6 times higher in fish fed CO and DO diets than FO fed fish despite the lower ARA suppliers from these VO-based diets, suggesting endogenous LC-PUFA biosynthesis from PUFA precursors in fish fed these VO. The fads2 and elovl5 gene expression levels in liver of fish fed DO were also higher compared to FO controls. Therefore, all the results support the hypothesis that African catfish has higher biosynthesis capacity to convert vegetable n-6 PUFA precursors like linoleic acid (LNA, 18:2n-6) into n-6 LC-PUFA of the ARA type, compared to the conversion of vegetable α-linolenic acid (ALA, 18:3n-3) into n-3 LC-PUFA of the eicosapentanoic acid (EPA) or docosahexanoic acid (DHA) type. The results also indicate that DO can be recommended as the best alternative to FO replacement in African catfish nutrition.

Effects of dietary lipid sources on the intestinal microbiome and health of golden pompano (Trachinotus ovatus)

Replacement of fish oil (FO) with vegetable oils (VO) in diets is economically desirable for the sustainable development of the aquaculture industry. However, inflammation provoked by FO replacement limited its widely application in fish industry. In order to understand the mechanism of VO-induced inflammation, this study investigated the impact of different dietary vegetable oils on the intestinal health and microbiome in carnivorous marine fish golden pompano (Trachinotus ovatus). Three diets supplemented with fish oil (FO, rich in long-chain polyunsaturated fatty acids), soybean oil (SO, rich in 18:2n-6) and linseed oil (LO, rich in 18:3n-3), respectively, were fed on juvenile golden pompano for 8 weeks, and the intestinal histology, digestive enzymes activities, immunity and antioxidant indices as well as intestinal microbiome were determined. The results showed that dietary SO significantly impaired intestinal health, and decreased the number and height of intestinal folds, and muscle thickness, as well as the zonula occludens-1 (zo-1) mRNA expression in intestine. Moreover, the two dietary VO significantly decreased the amylase and lipase activities in intestine, and reduced the trypsin activity in the dietary SO group. Furthermore, the two VO diets increased intestinal acid phosphatase (ACP) activity, while intestinal lysozyme (LZM) activity and serum diamine oxidase (DAO) activity in the SO group were also significantly increased (P < 0.05). Analysis of the intestinal microbiota showed that the two VO diets significantly increased the abundance of intestinal potentially pathogenic bacteria (Mycoplasma and Vibrio) and decreased proportions of intestinal probiotics (Bacillus and Lactococcus), especially in the dietary SO group. These results indicate that complete replacement of FO with VO in diets would induce intestinal inflammation and impair intestinal function, which might be due to changes in intestinal microbiota profiles, and that dietary SO would have a more negative effect compared to dietary LO on intestinal health in T. ovatus.

Effects of the complete replacement of fish oil with linseed oil on growth, fatty acid composition, and protein expression in the Chinese mitten crab (Eriocheir sinensis)

BackgroundThe finite marine resources make it difficult for us to obtain enough fish oil (FO) used in aquatic feeds. Another sustainable ingredients should be found to substitute FO. The effects of replacing FO with vegetable oil have been studied in a variety of crustaceans, but most studies have focused on the phenotypic effects. Little is known about the mechanisms of the effects.MethodsTo understand the molecular responses during the replacement of FO in Eriocheir sinensis, we investigated the effects of feeding FO or linseed oil (LO) on growth performance, digestive enzyme activity, fatty acid composition and protein expression in E. sinensis. Twenty-four juvenile crabs were fed diets containing FO or LO for 112 days. Weight, carapace length and width were recorded. Fatty acid composition of the diets and the hepatopancreas and protein expression in the hepatopancreas were analyzed.ResultsGrowth performance and molting interval were unchanged by diet. Crabs fed FO and LO had same activity of lipase and amylase, but comparing with crabs fed LO, crabs fed FO had higher trypsin activity and lower pepsin activity. Hepatopancreas fatty acid composition changed to reflect the fatty acid composition of the diets. In total, 194 proteins were differentially expressed in the hepatopancreas between the diets. Expression of heat shock proteins was higher in crabs fed LO. Expression of fatty acid synthase, long-chain fatty acid transport protein 4, acyl-CoA delta-9 desaturase, and fatty acid-binding protein 1, was higher in crabs fed FO.ConclusionsThe substitution of FO with LO didn’t have any effects on the growth and molting of mitten crab, but could significantly decrease the ability of mitten crab to cope with stress. The high content of HUFAs in the hepatopancreas of mitten crab fed FO is due to the high abundance of the proteins relative to the transport of the HUFAs. These findings provide a reason of the high content of EPA and DHA in crabs fed with FO, and provide new information for the replacement of FO in diets of mitten crab.

Macronutrient Requirements of Silvery-Black Porgy (Sparidentex hasta): A Comparison with Other Farmed Sparid Species

Silvery-black porgy (Sparidentex hasta) is recognized as one of the most promising fish species for aquaculture diversification in the Persian Gulf and the Oman Sea regions. In this regard, S. hasta has received considerable attention, and nutritional studies focused on establishing the nutritional requirements for improving diet formulation have been conducted during recent years. Considering the results from different dose–response nutritional studies on macronutrient requirements conducted in this species, it can be concluded that diets containing ca. 48% crude protein, 15% crude lipid, 15% carbohydrates and 20 KJ g−1 gross energy are recommended for on-growing S. hasta juveniles. In addition, the optimum essential amino acid profile for this species (expressed as g 16 g N−1), should be approximately arginine 5.3, lysine 6.0, threonine 5.2, histidine 2.5, isoleucine 4.6, leucine 5.4, methionine + cysteine 4.0 (in a diet containing 0.6 cysteine), phenylalanine + tyrosine 5.6 (in a diet containing 1.9 tyrosine), tryptophan 1.0 and valine 4.6. Moreover, the optimum dietary n-3 long chain polyunsaturated fatty acids and soybean lecithin are recommended to be 0.8% and 6%, respectively. The maximum replacement of fish meal with soy protein is recommended to be between 16.5% and 27.3%. In addition, different vegetal oil sources are also recommended for partial and almost complete replacement of fish oil in diets. Although the nutritional requirements in terms of macronutrients have been established under laboratory conditions, the analysis of the available literature indicate that future studies need to be conducted using a more holistic approach under intensive farming conditions in which different nutrients or additives need to be tested under different rearing conditions for refining nutrient requirements in this species.

Macronutrient Requirements of Silvery-Black Porgy (Sparidentex hasta): A Comparison with Other Farmed Sparid Species

Silvery-black porgy (Sparidentex hasta) is recognized as one of the most promising fish species for aquaculture diversification in the Persian Gulf and the Oman Sea regions. In this regard, S. hasta has received considerable attention, and nutritional studies focused on establishing the nutritional requirements for improving diet formulation have been conducted during recent years. Considering the results from different dose–response nutritional studies on macronutrient requirements conducted in this species, it can be concluded that diets containing ca. 48% crude protein, 15% crude lipid, 15% carbohydrates and 20 KJ g−1 gross energy are recommended for on-growing S. hasta juveniles. In addition, the optimum essential amino acid profile for this species (expressed as g 16 g N−1), should be approximately arginine 5.3, lysine 6.0, threonine 5.2, histidine 2.5, isoleucine 4.6, leucine 5.4, methionine + cysteine 4.0 (in a diet containing 0.6 cysteine), phenylalanine + tyrosine 5.6 (in a diet containing 1.9 tyrosine), tryptophan 1.0 and valine 4.6. Moreover, the optimum dietary n-3 long chain polyunsaturated fatty acids and soybean lecithin are recommended to be 0.8% and 6%, respectively. The maximum replacement of fish meal with soy protein is recommended to be between 16.5% and 27.3%. In addition, different vegetal oil sources are also recommended for partial and almost complete replacement of fish oil in diets. Although the nutritional requirements in terms of macronutrients have been established under laboratory conditions, the analysis of the available literature indicate that future studies need to be conducted using a more holistic approach under intensive farming conditions in which different nutrients or additives need to be tested under different rearing conditions for refining nutrient requirements in this species.

The Effect of Replacement of Fish Oil by Soybean Oil in Practical Diets, on Tissue Fatty Acid and Expression of Related Genes in Pacific White Shrimp Litopenaeus vannamei

High prices and unsustainable supply have rendered the use of high levels of fish oil in aquafeeds problematic. In the present study, an eight-week feeding trial was conducted to evaluate the replacement of fish oil with less expensive and more sustainable soybean oil in a practical diet containing 17% fish meal, which is widely used in China for Pacific white shrimp Litopenaeus vannamei. Five diets with five levels of fish oil replacement (0%, 25%, 50%, 75%, and 100%) by soybean oil were fed to shrimp for 56 days. At the end of the trial results obtained after analysis of the shrimp showed that shrimp fed diets containing 50% fish oil and 50% soybean oil displayed no significant differences in weight gain, specific growth rate, survival, and feed conversion ratio. Quantitative polymerase chain reactions revealed that the expression levels of fatty acid binding protein and fatty acid synthase, two critical genes in fat metabolism, gradually decreased with increased levels of soybean oil in diets. Fatty acid profiling showed that complete replacement of fish oil with soybean oil affected fatty acid content in shrimp muscles, including monounsaturated fatty acid, polyunsaturated fatty acid, and highly-unsaturated fatty acid, as well as the ratio of n-3/n-6 polyunsaturated fatty acids. The expression of two genes decreased with increased soybean oil level in diets. The growth results indicate

Dietary Mannan Oligosaccharides: Counteracting the Side Effects of Soybean Meal Oil Inclusion on European Sea Bass (Dicentrarchus labrax) Gut Health and Skin Mucosa Mucus Production?

The main objective of this study was to assess the effects of 4 g kg−1 dietary mannan oligosaccharides (MOS) inclusion in soybean oil (SBO)- and fish oil (FO)-based diets on the gut health and skin mucosa mucus production of European sea bass juveniles after 8 weeks of feeding. Dietary MOS, regardless of the oil source, promoted growth. The intestinal somatic index was not affected, however dietary SBO reduced the intestinal fold length, while dietary MOS increased it. The dietary oil source fed produced changes on the posterior intestine fatty acid profiles irrespective of MOS dietary supplementation. SBO down-regulated the gene expression of TCRβ, COX2, IL-1β, TNFα, IL-8, IL-6, IL-10, TGFβ, and Ig and up-regulated MHCII. MOS supplementation up-regulated the expression of MHCI, CD4, COX2, TNFα, and Ig when included in FO-based diets. However, there was a minor up-regulating effect on these genes when MOS was supplemented in the SBO-based diet. Both dietary oil sources and MOS affected mean mucous cell areas within the posterior gut, however the addition of MOS to a SBO diet increased the mucous cell size over the values shown in FO fed fish. Dietary SBO also trends to reduce mucous cell density in the anterior gut relative to FO, suggesting a lower overall mucosal secretion. There are no effects of dietary oil or MOS in the skin mucosal patterns. Complete replacement of FO by SBO, modified the gut fatty acid profile, altered posterior gut-associated immune system (GALT)-related gene expression and gut mucous cells patterns, induced shorter intestinal folds and tended to reduce European sea bass growth. However, when combined with MOS, the harmful effects of SBO appear to be partially balanced by moderating the down-regulation of certain GALT-related genes involved in the functioning of gut mucous barrier and increasing posterior gut mucous cell diffusion rates, thus helping to preserve immune homeostasis. This denotes the importance of a balanced dietary n–3/n–6 ratio for an appropriate GALT-immune response against MOS in European sea bass juveniles.

Replacement of dietary fish oil with vegetable oils improves the growth and flesh quality of large yellow croaker (Larmichthys crocea)

We investigated the effect of the replacement of dietary fish oil with vegetable oils on the growth and flesh quality of large yellow croaker (Larmichthys crocea). The basal diet (FO) was formulated to contain 66.5% fish meal and 6.4% menhaden fish oil; whereas the other 3 experimental diets were formulated by replacing the fish oil with 50% soybean oil (SO50), 100% soybean oil (SO100) and 100% palm oil (PO100), respectively. The 4 diets were randomly assigned to 4 floating sea cages (3.0 m × 3.0 m × 3.0 m), and each was stocked with 250 fish individuals with an initial average weight of 245.29 g ± 7.45 g. The fish were fed to apparent satiation twice a day at 5:00 and 17:00, respectively, for 12 weeks. Experimental analysis showed that the specific growth rate of fish fed SO50 or PO100 were significantly higher than that of fish fed FO or SO100 (P 0.05). Compared to FO diet, SO50, SO100 and PO100 diets led to substantial decreases in the liquid loss and water loss from fresh fillets (1 d, 4°C) (P<0.05). Similarly, thiobarbituric acid reactive substance (TBARS) values of fillets under different storage conditions (1 d, 4°C; 7 d, 4°C; 4 weeks, −20°C; 8 weeks, −20°C) decreased significantly after partial or complete replacement of fish oil with vegetable oils. These findings indicated that the growth performance and selected flesh quality properties (liquid holding capacity and TBARS value) of large yellow croaker were substantially improved by replacing dietary fish oil with vegetable oils.

Culture performance and tissue fatty acid compositions of yellow perch (Perca flavescens) fed different dietary lipids

The partial or total replacement of fish oil with soybean oil or flax oil in yellow perch Perca flavescens rearing performance and tissue fatty acid compositions were evaluated using five isonitrogenous (43.2%), isolipidic (8.5%), and isocaloric (21.3MJ/kg) diets in a 15-week trial. Dietary treatments consisted of: 1) FO, containing 100% fish oil, which was used as a control; 2) FO:FXO, a 1:1 mixture of fish oil and flaxseed oil; 3) FXO, containing 100% flaxseed oil; 4) FXO:SO, a 1:1 mixture of flaxseed oil and soybean oil; and 5) SO, containing 100% soybean oil. Partial or complete replacement of fish oil with flaxseed oil (FO:FXO and FXO) resulted in similar final body weight, weight gain, specific growth rate, and feed efficiency compared to fish fed the FO diet, but fish fed the FXO:SO and SO diets had lower weight gain, specific growth rate and feed efficiency compared to other treatments. Somatic indices were similar for all diets except for gonadal somatic index which was higher for SO. Fillet proximate composition was similar for all diets; however replacing fish oil with different vegetable oils resulted in decreased n-3 fatty acids and increased n-6 fatty acids in various tissues. When fish oil was completely removed, concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 decreased by 70, 46, and 33%, respectively, from values for fish fed the FO diet. Flaxseed oil can partially replace fish oil in the diet of yellow perch while maintaining growth performance and a favorable n‐3:n‐6 fillet fatty acid profile.