Effect of fermented Enteromopha prolifera on the growth performance,digestive enzyme activities and serum non‐specific immunity of red tilapia (Oreochromis mossambicus × Oreochromis niloticus)

This study was conducted to evaluate the effect of dietary inclusion of different levels of fermented macroalga, Enteromorpha prolifera, on the growth performance, digestive enzyme activities and serum non‐specific immunity of red tilapia (Oreochromis mossambicus × Oreochromis niloticus). Fish were fed the control diet or the five diets supplemented with fermented E. prolifera for 7 weeks (diets 1–5 containing 10, 20, 30, 40 and 50 g kg^?1 of fermented E. prolifera respectively). The results showed that the percentage weight gain and specific growth rate (SGR) improved significantly in fish fed diets 3, 4 and 5, and regression analysis showed SGR reached the maximum in fish fed diet containing 37 g kg^?1 fermented E. prolifera, while the feed conversion ratio reduced significantly in fish fed diets 2, 3, 4 and 5, and regression analysis showed it reached its minimum in fish fed diet containing 41 g kg^?1 fermented E. prolifera. The pepsin, erepsin, gastric amylase, intestinal amylase, gastric lipase and intestinal lipase activities in fish fed diets 2, 3 and 4 were higher significantly than the control, with the exception of the pepsin activity in fish fed diet 4. The serum total superoxide dismutase, lysozyme, acid phosphatase and alkaline phosphatase activities enhanced significantly in fish fed diets 3 and 4. In conclusion, fermented E. prolifera had positive effects on the growth performance, digestive enzyme activities and serum non‐specific immunity of red tilapia and the recommended dose of fermented E. prolifera is 37–41 g kg^?1 in the diet of red tilapia.     

Effects of dietary arginine on growth performance,feed utilization,haematological parameters and non‐specific immune responses of juvenile Nile tilapia (Oreochromis niloticus L.)

An 8‐week feeding trial was conducted to evaluate the effects of dietary arginine on growth performance, feed utilization, haematological parameters and non‐specific immune responses of juvenile Nile tilapia (6.03 g). Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐arginine (8.5 g kg^?1, 11.5 kg^?1, 15.3 kg^?1, 18.8 kg^?1 and 22.4 kg^?1 dry diet) from dietary ingredients and crystalline arginine. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (6.04 ± 0.02 g) three times daily (8:30, 12:30, and 17:00 hours) to apparent satiation. Results showed that the weight gain (WG) and special growth rate (SGR) increased with increasing dietary arginine levels up to 15.3 kg^?1 and remained nearly the same thereafter. Arginine supplementation had no impact on the survival, body composition and haematological parameters of tilapia. However, the immune responses (plasma nitric oxide content, total nitric oxide synthase (T‐NOS) and lysozyme activity) significantly (P < 0.05) increased with increasing dietary argentine level after stress. Quadratic regression analysis (y = ?0.7147x² + 25.986x + 147.53 R² = 0.8736) on weight gain against dietary arginine levels indicated that the optimal dietary arginine requirement was estimated to be 18.2 kg^?1 of the diet (corresponding to 6.24% of dietary protein on a dry weight basis). The present study indicates that arginine has an immunostimulatory potential to help juvenile Nile tilapia cope with stress conditions such as Streptococcus iniae infection.     

Effects of glycopeptides on development,growth and non‐specific immunity of pearl oyster Pinctada fucata (Gould)

The effects of glycopeptides, prepared from pearl oyster Pinctada fucata, on embryonic development, larval and juvenile growth and adult non‐specific immunity of P. fucata were investigated in this study. Glycopeptides had a pronounced stimulatory effect on embryonic development and larval and juvenile growth of P. fucata. enhancing with increased glycopeptide concentrations. All of haemocytes, phagocytosis, aggregation, serum microbiostatic activity and bacteriocidal activity all showed significant increases after 60‐day feeding, relative to unfed controls. The major conclusion is that glycopeptides had a pronounced stimulatory effect on the non‐specific immunity of pearl oysters.     

Effects of dietary carbohydrate and lipid levels on growth performance,feed utilization,body composition and non‐specific immunity of large yellow croaker (Larimichthys crocea)

The present study was conducted to investigate the effects of dietary lipid, carbohydrate and their interactions on growth performance, feed utilization, body composition and non‐specific immunity of large yellow croaker (Larimichthys crocea). The experimental fish were fed the diets with graded levels of dietary crude lipid (80, 110 and 140 g/kg diet) and dietary carbohydrate (60, 90 and 120 g/kg diet) for 7 weeks. Results showed that the specific growth rate decreased significantly as dietary carbohydrate increased, which partly resulted from the progressively reduced feed intake and protein efficiency ratio. Meanwhile, the result of postprandial glucose content confirmed glucose intolerance of the croaker. However, the specific growth rate was not significantly altered by dietary lipid, but the feed intake was remarkably reduced. The different growth performance and feed utilization of croaker in response to dietary lipid and carbohydrate resulted in the variation of body composition. In addition, the activity of lysozyme and classical complement pathway was significantly improved in croaker fed the diet with 110 g/kg lipid. In above, dietary carbohydrate and lipid of large yellow croaker should be maintained at 60 and 110 g/kg diet, respectively, based on the above indices.     

Effects of dietary peptide intake on growth,energy budget,body composition and non‐specific immunity of the sea cucumber Apostichopus japonicus (Selenka)

In this study, a 60‐day feeding trial was conducted to determine the effects of feed supplementating the feed of Apostichopus japonicus with peptides on its growth, energy budget, body composition and immune responses. Sea cucumbers were fed with five experimental diets supplemented with different proportions of peptides: 0 (D1), 12.5 (D2), 25 (D3), 37.5 (D4) and 50 (D5) g/kg in basal diet. Our results suggested that specific growth rate (SGR) and ratio of viscera to body wall (RVBW) of sea cucumbers fed with D4 were significantly improved. Relative to D1, ingestion rate (IR) and faeces production rate (FPR) for D3 and D4 were reduced considerably. Notably, the energy intake increased when peptide level increased from 0 to 50 g/kg. Meanwhile, the energy deposited for growth increased, and the energy loss decreased when peptide level increased from 0 to 37.5 g/kg. The sea cucumbers in D4 had the highest level of crude fat and lowest crude ash. The activities of immunoenzyme, such as SOD, CAT, T‐AOC, ACP and AKP, increased with peptide increase. Results suggested that supplementation of the feed with 25–37.5 g/kg peptides could significantly improve the growth performance, body composition and immune capacity of Apostichopus japonicus.     

Beneficial effects of dietary exogenous protease on the growth,intestinal health and immunity of GIFT (Oreochromis niloticus) fed plant‐based diets

This study investigated the effects of dietary exogenous protease on the growth performance, intestinal health, immune parameters and disease resistance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Five test diets with commercial protease at the levels of 0, 1.38, 2.76, 5.52 and 11.04 U/g (named PE0, PE1, PE2, PE5 and PE11, respectively) were administered to triplicate tanks with 30 fish for 60 days, and then, the fish were challenged with Streptococcus agalactiae for 14 days. The results indicated that weight gain increased as exogenous protease increased from 0 to 5.52 U protease/g diet and then decreased significantly (p < .05) with a further increase in exogenous protease supplementation (p < .05). The height of the villi in the proximal intestine and distal intestine, the width of the villi in three segments of the intestine, and the thickness of the muscle layer in the proximal intestine and mid‐intestine (p < .05) were increased in the fish fed the PE5 diet. Immune and antioxidant indices (except malondialdehyde), and survival after challenged with S. agalactiae were higher in fish fed PE5 diets than in those fed other diets (p < .05). In conclusion, 5.52 U/g protease supplementation in a plant‐based diet could promote the growth performance, intestinal physical barrier function, innate immunity and S. agalactiae resistance of GIFT.     

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.     

Effects of dietary Yucca meal on growth,haematology, non‐specific immune responses and disease resistance of juvenile Nile tilapia,Oreochromis niloticus (Linnaeus, 1758)

A 10‐week feeding trial was conducted to determine the effects of dietary yucca meal supplementation on growth, haematology, non‐specific immune responses and disease resistance in juvenile Nile tilapia, Oreochromis niloticus. Six isonitrogenous and isoenergetic experimental diets were formulated to contain 0% (YMS₀), 0.1% (YMS_0.1), 0.3% (YMS_0.3), 0.5% (YMS_0.5), 1% (YMS_1.0) and 2% (YMS_2.0) dietary yucca meal on the dry weight basis. Results of this study showed a higher growth performance for YMS_0.1 group with significant differences with YMS_0.5, YMS_1.0 and YMS_2.0 groups. In addition, whole‐body protein content of fish fed the YMS_0.1 diet was significantly higher as compared to YMS₀. Plasma lysozyme activity significantly increased in YMS_0.1 group comparing to YMS₀ and YMS_0.5 groups. Respiratory burst activity of phagocytic blood cells was significantly enhanced when fish were fed the YMS_0.1 diet. Results also showed that yucca meal supplementation had moderate effects on glutamic oxaloacetic transaminase and cholesterol levels. After the 14‐day challenge test with Aeromonas hydrophila, cumulative survival of fish fed YMS_0.1 diet was significantly higher than that of fish fed diet YMS₀, YMS_1.0 and YMS_2.0. These results suggest that the optimum dietary yucca meal inclusion level in the diet of juvenile Nile tilapia could be between 0.1% and 0.14% (23.9~33.4 mg kg^?1 saponin) as a feed additive to promote growth, enhance the non‐specific immune responses and increase disease resistance.     

猪油对罗非鱼生长及餐后脂质代谢的影响

在实用饲料配方的基础上分别添加0%、5%、10%猪油组成试验饲料饲喂罗非鱼(Oreochromis niloticus)(初重43 g)8周,比较研究猪油不同添加水平对罗非鱼生长及餐后脂质代谢的影响。结果表明,罗非鱼的末重(FBW)、特定生长率(SGR)、增重率(WGR)和饲料效率(FE)随着饲料中猪油水平的增加而显著升高。而摄食量(FI)表现出相反的变化趋势,即高水平猪油组显著低于对照组。随猪油添加水平增加,罗非鱼肝胰脏超氧化物歧化酶(SOD)、谷丙转氨酶(ALT)和谷草转氨酶(AST)活力显著降低,而肝脏丙二醛(MDA)含量显著增加。血清中甘油三酯(TG)、胆固醇(CHO)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)和极低密度脂蛋白胆固醇(VLDL-C)含量均随饲料中猪油水平增加而显著升高。各试验组罗非鱼血清中CHO、TG、LDL-C和VLDL-C含量随时间推移均表现出先升高后降低的变化趋势,TG和VLDL-C的峰值出现在餐后6h,而CHO和LDL-C峰值在餐后9 h。但HDL-C表现出相反的变化趋势,即先降低后升高,在餐后6 h达到最低值。总之,饲料中添加不同水平猪油会促进罗非鱼生长,但会影响罗非鱼的肝功能以及餐后脂质代谢,罗非鱼抗氧化能力也相应受到影响。     

Effects of dietary cecropin on growth,non‐specific immunity and disease resistance of tilapia (Oreochromis niloticus × O. aureus)

An 8‐week feeding trial was conducted to evaluate the effect of dietary cecropin on growth performance, non‐specific immunity and disease resistance of hybrid tilapia (Oreochromis niloticus × O. aureus). A basal diet was supplemented with 0 (control), 75, 150 and 225 mg kg^?1 cecropin to formulate four experimental diets. The results showed that final body weight and specific growth rate obtained with diet 150 mg kg^?1 cecropin were significantly higher (P < 0.05) than that obtained with diets 0 and 75 mg kg^?1, whereas there was no difference between 150 and 225 mg kg^?1. Feed conversion efficiency was improved by increasing the dietary cecropin content (P < 0.05). However, feeding intake was reduced as dietary cecropin increased. Serum lysozyme, alkaline phosphatase, catalase and superoxide dismutase activity were significantly increased with the increased levels of dietary cecropin (P < 0.05), and reached a maximum at level of 150 mg kg^?1 cecropin, then those values no longer increased. Moreover, the dietary cecropin supplementation level also exhibited a decrease in the cumulative mortality rates compared with the controls when challenged with Aeromonas veronii. The results suggested that the dietary supplementation of cecropin could improve the growth, non‐specific immunity indicators and resistance of hybrid tilapia against A. veronii.     

Effect of cannabis oil on growth performance,haematology and metabolism of Nile Tilapia Oreochromis niloticus

Cannabis sativa is a plant that produces an oil with psychoactive and stress reduction effects and thus illegal in many nations. Lately, the beneficial properties of the plant extract are becoming better understood and perceptions are changing. As the aquaculture industry matures from a primitive extensive pond system to an industrialized intensive system, fish stress and disease incidence are increasing, with negative economic results. A nutritional ingredient that could reduce stress and disease incidence in aquacultured fish would thus be opportune. In the present work we investigated whether ether extracted cannabis oil would relieve stress, improve growth and feed conversion, and/or improve haematological indicators of disease resistance. Three diets were made to contain either soy oil, industrial hemp oil or cannabis oil and offered to tilapia for 8 weeks. At termination, survival, growth, feed conversion and blood parameters were assessed. Fish were returned to their tanks, offered the same feeds as during the experiment and respiration assessed. Cannabis extract was found to increase metabolism and thus increase feed conversion. On the other hand, cannabis had no effect on blood cell counts, total plasma protein, haematocrit or lysozyme activity. Results thus suggest that cannabis does not improve immune response of tilapia or body composition but does reduce growth rate by increasing metabolic rate.     

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.     

Preliminary study to evaluate the effects of dietary bile acids on growth performance and lipid metabolism of juvenile genetically improved farmed tilapia (Oreochromis niloticus) fed plant ingredient‐based diets

A 9‐week feeding experiment was conducted to investigate the effects of dietary bile acids (BAs) on juvenile genetically improved farmed tilapia (GIFT) (Oreochromis niloticus) based on the evaluations of growth performance and parameters relevant to lipid metabolism. Each of five vegetable protein‐based diets containing BAs at a level of 0, 0.05, 0.15, 0.45 or 1.35 g/kg diet was fed to three replicates with 40 fish (8.2 g per fish). The results showed that weight gain (WG) increased significantly with the increase in BAs from 0 to 0.15 g/kg diet and then decreased significantly at a higher BA supplementation. Dietary BAs significantly reduced the crude lipid content in the whole body, muscle and liver tissue of GIFT. Fish fed diet with 1.35 g BAs/kg diet developed serious nuclear migration and vacuolization in hepatocytes. Gall bladder appeared to contain white solid and has fragile capsules. Dietary BA supplementation had significant effects on serum biochemical indices and activities of lipid metabolism enzymes in liver and intestine. In conclusion, dietary bile acid supplementation (0.15 g/kg) can facilitate the lipid metabolism and therefore promote the growth of tilapia. However, overdosed dietary BAs induced gallstone development, disrupted lipid metabolism and depressed the growth performances of GIFT.     

Effect of dietary bovine lactoferrin on growth,haematology and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of dietary lactoferrin (Lf) on growth, haematology and non‐specific immune response of rainbow trout Oncorhynchus mykiss (Walbaum). Fish were fed an experimental diet containing 0 (as control), 50, 100, 200 and 400 mg Lf kg^?1 diet twice daily for 8 weeks and sampled at 2, 4, 6 (immune function and growth), and 8 weeks (immune function, haematology and growth). Statistical analyses revealed no significant effects of dietary Lf on growth performance (specific growth rate, weight gain, feed conversion ratio, feed intake and condition factor) or haematological parameters (red and white blood cell count, haemoglobin, haematocrit, serum iron and total iron binding capacity [TIBC]). Among the serum non‐specific immune parameters, lysozyme activity increased significantly in fish fed 100, 200, or 400 mg Lf kg^?1 feed for 8 weeks, whereas haemolytic complement activity increased in fish fed 100 and 400 mg Lf kg^?1 diet after 6 weeks. The antiprotease activity increased in groups fed 100, 200 or 400 mg Lf kg^?1 diet after 8 weeks. However, no significant effect was observed on serum peroxidase level. It can be concluded that feeding of rainbow trout on the diet supplemented with 100 mg kg^?1 or higher for 8 weeks enhances the non‐specific immune response.     

Effects of dietary probiotic on the growth performance,non‐specific immunity and disease resistance of cobia,Rachycentron canadum

The present study was performed to investigate the effects of a commercially available probiotic product (compound probiotic) containing Bacillus subtilis 7.0 × 10⁹ CFU g^?1, Bacillus licheniformis 3.0 × 10⁹ CFU g^?1, Lactobacillus spp. 5.0 × 10⁸ CFU g^?1 and Arthrobacter spp. 1.0 × 10⁸ CFU g^?1 on the growth performance, non‐specific immunity and protection against Vibrio harveyi infection in cobia (Rachycentron canadum). Fish were fed diets containing six graded levels of compound probiotic (0.0, 1.0, 2.0, 3.0, 4.0 and 5.0 g kg^?1) for 8 weeks. The results showed that the survival rate ranged from 81.1% to 84.4% with no significant difference among dietary treatments (P > 0.05) after feeding experiment. Dietary compound probiotic significantly increased the specific growth rate (SGR), serum lysozyme, alternative complement pathway (ACP) activity, phagocytosis percentage (PP) and respiratory burst activity of head‐kidney macrophages of cobia. Moreover, feeding of supplemented diets containing compound probiotic resulted in significantly lower mortality against the pathogens Vibrio harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, an optimal dose of dietary compound probiotic administration determined by second‐order polynomial regression analysis was 3.3 g kg^?1, on the basis of the SGR and mortality after challenge with V. harveyi.     

Effects of dietary immunostimulant combination on the growth performance,non‐specific immunity and disease resistance of cobia,Rachycentron canadum (Linnaeus)

The aim of this study was to examine the effects of the immunostimulant combination (IC) containing β‐glucan, A3α‐peptidoglycan, vitamin C and vitamin E on the growth performance, non‐specific immunity and protection against Vibrio harveyi infection in cobia (Rachycentron canadum). Fish were fed diets containing six graded levels of IC (0, 1, 2, 3, 4 and 5 g kg^?1 diet) for 8 weeks. The results showed that the survival rate ranged from 81.1 to 84.4% with no significant difference among all the groups (P > 0.05) after the feeding experiment. Dietary IC significantly increased the specific growth rate (SGR), serum lysozyme, alternative complement pathway (ACH50) activity, phagocytosis percentage (PP) and respiratory burst activity of head kidney macrophages of cobia. Moreover, feeding of supplemented diets containing 3.0 g kg^?1 IC resulted in significantly lower mortality against the pathogens, V. harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, the optimal dose of dietary IC administration, determined by second‐order polynomial regression analysis was 3.43 and 2.71 g kg^?1 diet, respectively, on the basis of the SGR and mortality after challenge with V. harveyi.     

饲料糖水平对吉富罗非鱼幼鱼生长和肝代谢功能的影响

为研究饲料糖水平对吉富罗非鱼幼鱼生长性能和肝代谢功能的影响,实验配制等蛋白、等脂肪含量的8种不同糖水平(10％、15％、20％、25％、30％、35％、40％和45％)饲料,每个糖水平设3个重复,饲养周期49 d,结果显示:(1)饲料糖水平对吉富罗非鱼幼鱼的增重率、成活率、饲料系数和肝体比均有显著影响(P＜0.05).饲料糖水平为35％时,罗非鱼增重最快;饲料糖水平为40％时饲料系数最低.(2)随着饲料糖水平的升高,鱼体肌糖原、粗脂肪含量逐渐升高,鱼体肝糖原含量先增加后下降.(3)饲料糖水平对各组鱼血清谷草转氨酶、谷丙转氨酶、血清磷酸果糖激酶活性、总蛋白和总胆汁酸浓度均有显著影响(P＜0.05),且随着糖水平的升高,呈上升趋势;而鱼体肝酯酶和脂蛋白脂酶活性则是先上升后下降.(4)饲料糖水平35％时,肝脏组织出现少量细胞脂滴空泡状现象;饲料糖水平40％和45％时,肝脏组织切片有明显的细胞脂滴空泡状、核偏移和细胞质消失现象.肝脏脂滴空泡状面积率与组织脂肪含量具有显著的正相关,与肝脏组织的脂肪肝病变程度成正比.结果表明,吉富罗非鱼苗种饲料以29.10％～ 35.00％的糖水平较利于吉富罗非鱼幼鱼生长及后期的脂肪肝病预防.     

Influence of several non‐nutrient additives on nonspecific immunity and growth of juvenile turbot,Scophthalmus maximus L.

The effects of three non‐nutrient additives on nonspecific immunity and growth of juvenile turbot (Scophthalmus maximus L.) were studied in this feeding experiment. The five treatments are basal diet alone, basal diets containing three different additives [0.4 g kg^?1 of xylo‐oligosaccharides (XOS), 1.3 g kg ^?1 of yeast cell wall and 0.8 g kg ^?1 of bile acids] individually or in combination. Two hundred and twenty‐five turbots (average initial weight 151.3 ± 11.3 g) were randomly allotted in five treatments with three replicates within each treatment in a 72‐day period. Comparing with basal diet group, activities of C3, C4, phagocyte, lysozyme, specific growth rate and feed conversion rate in yeast cell wall, XOS and the combined groups was enhanced significantly (P < 0.05); however, these parameters in bile acid groups were increased slightly (P > 0.05) except for phagocyte (P < 0.05); superoxide dismutase activity in additive groups was not significantly increased (P > 0.05) except for the combined group (P < 0.05). In conclusion, supplementation of yeast cell wall and XOS enhanced the nonspecific immunity of juvenile turbot. Synergistic or additive effect of the three additives was not observed.     

The synthetic antioxidant, ethoxyquin, adversely affects immunity in tilapia (Oreochromis niloticus)

Ethoxyquin (EQ) has been used as an antioxidant in livestock, aquaculture and pet foods. Animal food safety law has established the upper limit of EQ in animal feed at 150 mg kg⁻¹. However, the risk of EQ at the approved level for aquaculture feed (150 mg kg⁻¹) to fish health is unknown. Here, we examine the effect of EQ on the immunity of tilapia ( Oreochromis niloticus ). EQ concentration in the blood reached 0.16 mg L⁻¹ in fish fed EQ at the approved level. This level of EQ inhibited phagocytic activity of leucocytes in vitro and antibacterial activity of whole blood in vivo . Furthermore, pyknosis in the liver was observed throughout the duration of feeding. However, after 30 days of experimental challenge with feed containing 150 mg kg⁻¹ of EQ, no significant difference was observed in mortality. Although EQ at the approved level in feed causes immunosuppression in fish, the severity of immunosuppression does not lead to a lowering of disease resistance for short feeding periods.