Use of vitamin C as an immunostimulant. Effect on growth,nutritional quality,and immune response of <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.)

Teleost fish lack the enzyme for endogenous synthesis of ascorbic acid (AA), an essential micronutrient for fish. The aim of this study was to examine the effect of higher levels of dietary vitamin C on growth, nutritional quality, and immunomodulation in the Indian major carp, rohu (Labeo rohita). Four groups of L. rohita were fed experimental diets containing either no vitamin C (control) or supplemented with vitamin C at 500 mg kg⁻¹ (Exp-1), 1000 mg kg⁻¹ (Exp-2), or 1500 mg kg⁻¹ (Exp-3) for 60 days. Growth parameters (NWG, ADG, and SGR), serological parameters (TSP, TSA, TSG, and A:G), haematological parameters (TLC, TEC, Hct, MCV, and MCH), and different non-specific immunological parameters (PR, PI, respiratory burst activity, and bactericidal activity) were evaluated during the experimental trial. Fish fed a vitamin C-supplemented diet showed higher specific growth rate (SGR) up to 1000 mg kg⁻¹ compared with control fish. Different haematological and serological parameters along with non-specific immune parameters were influenced by vitamin C supplementation. Among the non-specific immune parameters phagocytic activity (PR and PI) and respiratory burst activity (NBT cells) were significantly (P ≤ 0.05) enhanced by increasing doses of vitamin C supplementation. Higher levels of dietary vitamin C significantly (P ≤ 0.05) enhanced protection against Aeromonas hydrophila (AH1) infection compared with controls. Results from this study help to establish the beneficial effect of vitamin C on growth and immunmodulation in rohu (L. rohita).     

Effect of dietary chromium picolinate on growth performance and blood parameters in grass carp fingerling, <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>

An experiment was conducted to investigate the effect of dietary chromium picolinate supplement on growth and haematology parameters of grass carp, Ctenopharyngodon idellus. Six diets with increasing dietary chromium picolinate levels 0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg kg⁻¹ were fed to triplicate groups of 20 fish (initial weight of 12.78 ± 1.16 g, mean ± SD) in a flow water system for 10 weeks. Fish fed the diet supplemented with 0.8 mg Cr kg⁻¹ had significantly improved weight gain (WG), feed efficiency ratio (FER), protein efficiency ratio (PER) and protein retention (PR). Fish fed high-chromium diets exhibited lower whole-body crude lipid contents than fish fed low-chromium diets. Liver glycogen concentrations for fish fed the diet with 0.2 mg Cr kg⁻¹ was the highest (77.67 mg g⁻¹). Fish fed the diet supplemented with 1.6 and 3.2 mg Cr kg⁻¹ had significantly lower liver glycogen concentrations than other groups (P < 0.05). The highest serum insulin concentrations were observed in fish fed the diet supplemented with 0.8 mg Cr kg⁻¹, but serum insulin concentrations decreased (P < 0.05) when dietary supplementation of chromium was higher than 0.8 mg Cr kg⁻¹. Cholesterol concentrations decreased in direct proportion to dietary chromium level and achieved the lowest level when the fish were fed the 0.8 mg Cr kg⁻¹ diet, but increased when the fish were fed the diet with more than 0.8 mg Cr kg⁻¹ (P < 0.05). Fish fed the diet supplemented with 0.8 mg Cr kg⁻¹ had higher triglyceride and high-density lipoprotein cholesterol (HDL-C) concentrations compared to other treatments. The results of the present study suggested that chromium picolinate could modify serum carbohydrate and lipid metabolism profile, and that the optimal dietary chromium level was 0.8 mg kg⁻¹ for grass carp according to growth.     

Effect of ethanolic extract of propolis on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of ethanolic extract of propolis (EEP) on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of EEP [0 (control), 1, 2, and 4 g kg⁻¹ diet] were fed to trout juveniles (mean weight 7.73 ± 0.17 g) for 10 weeks. Dietary EEP supplementation regardless of inclusion level significantly improved the specific growth rate of fish. Similarly, supplemental EEP generally improved the feed efficiency ratio and protein efficiency ratio, but no significant differences were observed between the 1 g kg⁻¹ EEP group and the control group. In addition, dietary EEP supplementation generally increased the plasma superoxide dismutase, lysozyme, total antioxidant capacity, glutathione peroxidase, and catalase activities, but decreased the plasma malondialdehyde level. The plasma triglycerides level was significantly lower in the 1 or 4 g kg⁻¹ EEP group as compared with the control group. Dietary EEP supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase activities, but increased the hepatic aspartate aminotransferase and alanine aminotransferase activities. These results indicate the potential to use the EEP as a growth promoter, hepatoprotective agent, and immunostimulant for rainbow trout.     

Purified deoxynivalenol or feed restriction reduces mortality in rainbow trout,Oncorhynchus mykiss (Walbaum), with experimental bacterial coldwater disease but biologically relevant concentrations of deoxynivalenol do not impair the growth of Flavobacterium psychrophilum

Diets containing deoxynivalenol (DON) were fed to rainbow trout Oncorhynchus mykiss (Walbaum) for 4 weeks followed by experimental infection (intraperitoneal) with Flavobacterium psychrophilum (4.1 × 10⁶ colony‐forming units [CFU] mL⁻¹). Mortality of rainbow trout fed either 6.4 mg kg⁻¹ DON or trout pair‐fed the control diet was significantly reduced (P < 0.05) in comparison with trout fed the control diet to apparent satiation (<0.1 mg kg⁻¹ DON). In a second experiment, trout were fed one of three experimental diets; a control diet, a diet produced with corn naturally contaminated with DON (3.3 mg kg⁻¹ DON) or a diet containing purified DON (3.8 mg kg⁻¹); however, these fish were not experimentally infected. The presence of DON resulted in significant reduction (P < 0.0001) in feed intake as well as weight gain after 4 weeks. Respiratory burst of head‐kidney leucocytes isolated from rainbow trout fed diets containing purified DON (3.8 mg kg⁻¹) was significantly higher (P < 0.05) at 35 day post‐exposure compared with controls. The antimicrobial activity of DON was examined by subjecting F. psychrophilum in vitro to serial dilutions of the chemical. Complete inhibition occurred at a concentration of 75 mg L⁻¹ DON, but no effect was observed below this concentration (0–30 mg L⁻¹).     

Dietary polysaccharide from <Emphasis Type="Italic">Angelica sinensis</Emphasis> enhanced cellular defence responses and disease resistance of grouper <Emphasis Type="Italic">Epinephelus malabaricus</Emphasis>

The purpose of this study was to determine the effect of Angelica sinensis polysaccharide (ASP) supplemented in diet on the innate cellular immune response and disease resistance in grouper, Epinephelus malabaricus. Fish were fed diets containing different doses of ASP (0, 500 and 3,000 mg kg⁻¹ diet) for 12 weeks. After 12 week feeding, the respiratory burst activity, phagocytic activity, and leukocytes proliferation in head kidney were assayed. The functional immunity in terms of cumulative mortality was also assessed by a challenge with live Edwardsiella tarda. Results showed that the respiratory burst activities in ASP-supplemented groups were increased significantly. The respiratory burst index was the highest in fish-fed 3000 mg kg⁻¹ diet and the lowest in control. The phagocytic activities in ASP-supplemented groups were significantly higher than that of control. No significant difference in phagocytic activity was observed between ASP-supplemented groups. ASP stimulated the head kidney leukocytes proliferation significantly, despite the absence of lipopolysaccharide (LPS) or not. The cumulative mortalities of fish fed with 3000 mg ASP kg⁻¹ diet were significantly lower than those fed with 500 mg ASP kg⁻¹ diet and control diet after 96 h of challenge. In conclusion, dietary ASP enhanced some cellular immune parameters and disease resistance against E. tarda in grouper.     

Effect of long-term administration of dietary β-1,3-glucan on growth, physiological, and immune responses in Litopenaeus vannamei (Boone, 1931)

β-1,3-Glucan at different dietary doses was administered to enhance the growth, immunity, and survival against nitrite stress in Pacific white shrimp, Litopenaeus vannamei. Four different diets supplemented with 0, 250, 500, or 1,000 mg of β-1,3-glucan kg⁻¹ diets were fed to L. vannamei. Growth performance (weight gain and survival rate), physiological conditions (blood total protein, glucose, lactate, triacylglycerols, cholesterol levels) and immunological responses (superoxide dismutase, catalase, lysozyme, acid phosphatase, and alkaline phosphatase activities) of shrimp were recorded after 84-day feeding and 120 h after exposed to nitrite-N. After 84-day feeding, 250 mg kg⁻¹ β-1,3-glucan diet resulted in better weight gain (P < 0.05). Before the nitrite stress, blood lactate, triacylglycerols, and cholesterol level in shrimp fed with 250 mg kg⁻¹ β-1,3-glucan diet were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Higher activities of catalase, lysozyme, and alkaline phosphatase were observed in shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan diet as compared to those obtained in shrimp fed with other diets (P < 0.05). After 120-h nitrite stress, blood protein, lactate, superoxide dismutase, catalase, and alkaline phosphatase activities in shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan were significantly higher than those observed in shrimp fed with other diets (P < 0.05). Glucose and triacylglycerol levels of shrimp fed with 500 or 1,000 mg kg⁻¹ β-1,3-glucan were significantly lower than those observed in other diets (P < 0.05). In shrimp fed with 500 and 1,000 mg kg⁻¹ β-1,3-glucan and 120-h after nitrite stress, the mortality was significantly lower than that observed in shrimp of control. Together, in this 84-day feeding trial, 250 mg kg⁻¹ β-1,3-glucan improved growth, whereas 500 mg kg⁻¹ β-1,3-glucan preferentially improved nitrite resistance, probably through accelerating energy metabolism and activating immune system.     

Effects of dietary propolis and vitamin E on growth performance and antioxidant status in juvenile rainbow trout (Oncorhynchus mykiss) under different flow rate

The present study investigated the effects of propolis and vitamin E supplementation in diets of juvenile rainbow trout subjected to two different flow rates (0.9 and 2.1 L min^?1) on growth performance, and vitamin A, C and E concentrations in tissues as well as malondialdehyde (MDA) levels. Juvenile rainbow trout were fed with diets containing 10 and 30 g propolis kg^?1, 60 mg kg^?1 vitamin E (Rovimix E‐50 adsorbate; min.%50 dl‐α‐tokopherly acetate) and without supplemented basal diet for 12 weeks. Weight gain (WG) in the C group was significantly lower (P < 0.05) than P10, P30 and E60 groups at both flow rate treatments. At 2.1 L min^?1, specific growth rate (SGR) in the C group was significantly lower (P < 0.05) than other groups, but at 0.9 L min^?1, SGR of fish did not differ among the diets groups (P > 0.05). Survival rate (SUR) was higher in propolis and vitamin E supplemented diet groups (P < 0.05) than control diet group at 0.9 L min^?1. Fish fed on diet E60 had higher (P < 0.05) tissue vitamin E concentration than fishes fed on other diets groups. Vitamin C concentration in rainbow trout tissues was significantly affected by the 30 g propolis supplemented diet group (P < 0.05), followed by the 10 g propolis supplemented diet group (P < 0.05). MDA level of E60 group was found significantly decreased instead of different than other groups (P < 0.05). The results of Student's t‐test revealed that WG, SGR, SUR values, vitamin (A, C, E) concentrations and MDA levels of tissues were negatively affected by 0.9 L min^?1flow rate treatment in juvenile rainbow trout.     

Effects of Haematococcus pluvialis supplementation on antioxidant system and metabolism in rainbow trout (Oncorhynchus mykiss)

Effects of commercial source for astaxanthin (Haematococcus pluvialis) (H.p) on antioxidant power, specific marker enzymes, and some metabolites were examined in rainbow trout (Oncorhynchus mykiss). Fish were fed on diets containing 1, 3, and 10 g microalga kg⁻¹ feed for 30 days. Serum total antioxidant activity and lipid peroxidation product, indicated by malondialdehyde (MDA), significantly enhanced with different doses of administration, indicating the elevated antioxidant status in all treatment groups. In group fed with high dose of alga, significantly elevated aspartate aminotransferase activity (AST) was noted, indicating damage of normal liver function in this group. Alkaline phosphatase (ALP) and alanine aminotransferase (ALT) were not affected in all groups. Although serum total protein remained unaffected, serum glucose level was decreased significantly in lower doses of administration. Furthermore, triglyceride and cholesterol levels showed significant decrease in 3 g kg⁻¹ microalga group by modulation of lipid metabolism in this group. On the other hand, in highest dose, significant increase in lipids was observed, indicating the slight dysfunction in lipid metabolism in this treatment group. The present study suggests that Haematococcus pluvialis especially in dose of 3 g kg⁻¹ feed administration may effectively enhance the antioxidant system and some biochemical parameters in rainbow trout.     

Effects of dietary riboflavin levels on antioxidant defense of the juvenile grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis>

This study was conducted to evaluate the effects of dietary riboflavin on antioxidant defense in the juvenile grouper Epinephelus coioides. Graded levels of riboflavin (0.9, 1.6, 4.4, 6.7, 12.9 and 19.4 mg kg⁻¹ dry diet) were fed to grouper juveniles (mean weight: 14.90 ± 0.46 g) for 12 weeks. Higher levels of liver thiobarbituric acid reactive substances (TBARS) content were observed in grouper fed low doses (0.9 and 1.6 mg kg⁻¹ diet) of riboflavin. Both liver glutathione reductase (GR) activity and its activation coefficient (GR-AC) poorly responded to riboflavin deficiency. In addition, other indices of the glutathione-dependent defense system, including the activities of glutathione peroxidase (GSH-PX) and glutathione-S-transferase (GST), and the content of glutathione (GSH), were also non-significantly affected by dietary riboflavin levels. However, the activities of liver superoxide dismutase (SOD) and catalase (CAT) were significantly lower in fish fed 0.9 mg kg⁻¹ diet, with a positive correlation between the different groups. In conclusion, the present study indicated that the juvenile grouper fed the riboflavin-unsupplemented diet was susceptible to lipid peroxidation (LPO), with lower SOD and CAT activities in the liver. However, the glutathione-dependent defense system of grouper was not affected by dietary riboflavin levels.     

Effect of dietary niacin on growth and body composition of two Indian major carps rohu, <Emphasis Type="Italic">Labeo rohita</Emphasis>, and mrigal, <Emphasis Type="Italic">Cirrhinus mrigala</Emphasis> (Hamilton), fingerlings based on dose–response study

An 15 week two set of feeding experiments were conducted to determine the dietary niacin requirement of Indian major carp fingerlings Labeo rohita and Cirrhinus mrigala, using casein gelatin–based diet. In both experiments, six isonitrogenous (40%) and isoenergetic (15.35 kJ g⁻¹) test diet, with graded levels of niacin (0–50 mg kg⁻¹ dry diet) in gradation of 10 mg kg⁻¹ dry diet, were formulated. In first experiment, fingerling of L. rohita (4.20 ± 1.22 cm; 0.632 ± 0.67 gm) were randomly stocked, in triplicate groups, in 55-L indoor polyvinyl flow-through system (1.5 L min⁻¹) and fed experimental diet at 0800 and 1600 h. Maximum live weight gain (1214%), feed conversion ratio (1.55) and protein efficiency ratio (1.60) were recorded at 30 mg dietary niacin diet. In second experiment, C. mrigala (4.50 ± 1.25 cm, 0.665 ± 0.88) were stocked in same setup. At the end of experiments, maximum live weight gain (1248%), FCR (1.47) and PER (1.70) occurred at 30 mg dietary niacin diet. However, the weight gain, FCR and PER data were analyzed by polynomial regression analysis indicating the requirement of niacin for L. rohita at 36.69, 33.06 and 32.0 mg kg⁻¹, respectively, and for C. mrigala at 35.19, 28.69 and 27.70 mg kg⁻¹ of dry diet, respectively. Whole body composition also showed significant (P < 0.05) differences among each other. On the basis of regression analysis of growth data, it is recommended that the diet for fingerlings should contain niacin at 33 and 30 mg kg⁻¹ dry diet for L. rohita and C. mrigala, respectively.     

Low fishmeal diets for Atlantic salmon, <Emphasis Type="Italic">Salmo salar</Emphasis> L., using soy protein concentrate treated with graded levels of phytase

The experiment aimed at determining the efficient use of phytase (Phy) in Atlantic salmon diets that had low (4.5%) fishmeal and contained 60% soy protein concentrate (SPC). Phytase was either included at 250, 500, 1,000 or 4,000 U Phy kg⁻¹ diet or the SPC was pre-treated prior to making diets using 250, 500 or 1,000 U Phy kg⁻¹ SPC. Fish were fed the experimental diets for 12 weeks, and there were no differences in survival among treatments nor were there differences in growth performance between the phytase-pre-treated SPC diets. Feed intake and weight gain were significantly lower for diets supplemented below 1,000 U Phy kg⁻¹ compared to all other diets. Apparent digestibility (AD) of phosphorus was significantly lower without the use of phytase (45.43 ± 2.06%) than for all other treatments. AD phosphorus increased from 55.70 ± 1.81% at the lowest phytase supplementation (250 U Phy kg⁻¹) to 80.87 ± 2.12% at the highest (4,000 U Phy kg⁻¹). There was no difference in AD phosphorus between the diet with the highest supplementation (4,000 U Phy kg⁻¹) and the pre-treated diets. There were no differences in whole-body dry material, crude protein or total lipid, whereas bone ash was significantly lower for diets supplemented below 1,000 U Phy kg⁻¹. Ash and phosphorus in the whole body and bone increased with increasing added phytase. At and above an inclusion of 1,000 U Phy kg⁻¹, bone ash (51.26 ± 0.12% bone weight) and bone phosphorus (11.21 ± 0.04% bone weight) reached concentrations that were no different to the pre-treated diets. In conclusion, phytase improved Atlantic salmon’s growth performance fed low fishmeal diets containing SPC, and at least 1,000 U Phy kg⁻¹ diet was required to have the same effect as pre-treatment of SPC with 250 U Phy kg⁻¹ SPC.     

Molecular cloning of cDNA of mammalian and chicken II gonadotropin-releasing hormones (mGnRHs and cGnRH-II) in the beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) and the disruptive effect of methylmercury on gene expression

Two gonadotropin-releasing hormone (GnRH) isoforms were identified in the beluga (Huso huso) brain by cDNA sequencing: prepro-mammalian GnRH (mGnRH) and prepro-chicken GnRH-II (cGnRH-II). The nucleotide sequences of the beluga mGnRH and cGnRH-II precursors are 273 and 258 base pairs (bp) long, encoding peptides of 91 and 86 amino acids, respectively. To investigate the effect of methylmercury (MeHg) on GnRH gene expression, animals were fed with four diets containing increasing levels of MeHg (0 mg kg⁻¹ [control]; 0.76 mg kg⁻¹ [low]; 7.8 mg kg⁻¹ [medium]; 16.22 mg kg⁻¹ [high]) for 32 days. The effects of MeHg on brain GnRH mRNA levels were evaluated by real-time PCR. A significant decrease in brain mGnRH and cGnRH-II mRNA levels were detected in fish receiving high dietary MeHg dose compared to controls on day 11 (P < 0.05). On day 18 and 32, all treatment groups had significantly lower brain mGnRH and cGnRH-II mRNA levels compared to the control group (P < 0.05). These findings demonstrate a disruptive role of MeHg on the level of brain mGnRH and cGnRH-II mRNAs in immature beluga.     

Changes in metabolic enzymes,cortisol and glucose concentrations of Beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) exposed to dietary methylmercury

In this paper, effects of dietary methylmercury (MeHg) on several blood biochemical parameters including GLU (glucose), LDH (lactate dehydrogenase), AST (aspartate aminotransferase), ALT (alanine aminotransferase), ALP (alkaline phosphatase) and cortisol were investigated in the Beluga sturgeon (Huso huso). Beluga juveniles were fed for 32 days on four diets containing MeHg (control: 0.04 mg kg⁻¹; low: 0.76 mg kg⁻¹; medium: 7.88 mg kg⁻¹; and high 16.22 mg kg⁻¹ treatment). Significant increases (P < 0.05) were observed in all biochemical parameters, except ALP levels, which decreased significantly (P < 0.05) compared to the control group with either dose- or time-dependent effects. These results suggest that long-term dietary MeHg exposure may affect metabolic enzyme activity and glucose levels in Belugas. These findings provide useful information for environmental and fishery officials to apply in future decisions for managing fish resources in Caspian Sea.     

Physiological effects of natural olive oil antioxidants utilization in rainbow trout (<Emphasis Type="Italic">Onchorynchus mykiss</Emphasis>) feeding

Olive mill vegetation water (VW) is an olive oil by-product rich in polyphenols has powerful antioxidant effects. In light of the interest on the research of novel natural antioxidants to use in fish feed, the aim of this research was to use VW as a potential substitute for artificial antioxidants in rainbow trout diet as well as checking its effects on the blood chemistry and digestive organ physiology of the fish. The experimental plan was monofactorial, balanced (4 × 3) and the experimental factor considered was the fish diet. Diets were isoproteic (CP 40%) and isoenergetic (18 MJ kg⁻¹ DM) with two inclusion levels of VW (1 and 5%: VW1 and VW5) tested against a control diet. A feeding trial was performed on quadruplicate groups of 200 fish (mean body weight: 44.2 g) fed experimental diets for 94 days. At the end of the trial, the growth performance traits were determined and sampling of blood and different tissues (brain, ovary, stomach, liver, and intestine) were carried out for haematology, endocrinology, histology, and digestive enzyme analysis. The main results of the present experimentation are that VW inclusion in rainbow trout feed slightly affects the productive traits and blood chemistry, while the histological structure of digestive organs and digestive enzyme physiology were not affected.     

Effect of prebiotic xylooligosaccharides on growth performances and digestive enzyme activities of allogynogenetic crucian carp (<Emphasis Type="Italic">Carassius auratus gibelio</Emphasis>)

The effect of prebiotic xylooligosaccharides (XOS) on the growth performance and digestive enzyme activities of the allogynogenetic crucian carp, Carassius auratus gibelio, was investigated. XOS was added to fish basal semi-purified diets at three concentrations by dry feed weight: diet 1, 50 mg kg⁻¹; diet 2, 100 mg kg⁻¹; diet 3, 200 mg kg⁻¹, respectively. Twelve aquaria (n = 20) with three replicates for each treatment group (diets 1–3) and control treated without XOS were used. Weights of all collected carp from each aquarium were determined at the initial phase and at the end of the experiment, and the carp survival was also determined by counting the individuals in each aquarium. After 45 days, there were significant differences (P < 0.05) in the relative gain rate (RGR), and daily weight gain (DWG) of diets 1–3 were compared with the control. However, the survival rate was not affected (P > 0.05) by the dietary treatments. For enzymatic analysis, dissection produced a crude mixture of intestine and hepatopancreas of each segment to measure. The protease activity in the intestine and hepatopancreas content of fish in diet 2 (487.37 ± 20.58 U g⁻¹ and 20.52 ± 1.93 U g⁻¹) were significantly different (P < 0.05) from that in the control (428.13 ± 23.26 U g⁻¹ and 12.81 ± 1.52 U g⁻¹) and diet 3 (428.00 ± 23.78 U g⁻¹ and 14.04 ± 1.59 U g⁻¹). Amylase activity in the intestine was significantly higher for diet 2 compared to diet 1 and the control. As for amylase in the hepatopancreas, assays showed higher activity in diet 2 (P < 0.05) compared to the rest.     

Influence of dietary garlic (Allium sativum) on the antioxidative status of rainbow trout (Oncorhynchus mykiss)

Oxidative damage by free radicals has been implicated in the pathogenesis of several diseases. In this study, the antioxidative effect of dietary garlic on rainbow trout was examined. Trout fingerlings were fed on diets containing 10, 20, 30, 40 and 50 g garlic powder kg^?1 diet. Serum lipid peroxides and activities of antioxidant enzymes were measured. Serum thiobarbituric acid reactive substances (TBARS) assay showed that garlic consumption that resulted in a significant decrease in lipid peroxidation. The lowest levels of TBARS were observed in fish fed diet supplemented with 30 g kg^?1 garlic. However, higher doses of garlic (40 and 50 g kg^?1 diet) caused no further reduction in serum TBARS. The results showed a significant increase in superoxide dismutase in all of the garlic‐treated groups compared with the control. Ingestion of 10, 20 and 30 g kg^?1 dietary garlic resulted in a significant reduction in the catalase activity compared with all but the 10 g kg^?1 group. There was no significant difference in glutathione peroxidase activity among the different groups. Serum alanine aminotransferase and aspartate aminotransferase levels increased significantly in trout‐fed diets containing 40 and 50 g kg^?1 garlic powder. These results suggest that dietary garlic may improve the antioxidant status of rainbow trout. However, undesirable effects of higher doses of garlic should be considered.     

The effect of vitamin E on the serum complement activity of the rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout were fed three experimental diets with varying levels of vitamin E (α‐tocopherol) supplementation (0, 100 and 1000 mg kg^?1 diet), and the effects of feeding these diets on serum spontaneous haemolytic activity and classical complement activity were investigated. Hepatic α‐tocopherol levels reflected the dietary intake of the vitamin. Fish fed the diet deficient in vitamin E showed reduced growth and increased mortality. Their hepatosomatic index and erythrocyte fragility was significantly higher than both the supplemented groups and haematocrit, and complement activity were all significantly lower. There appeared to be some enhancement of serum complement activity correlated with increased dietary supplementation with vitamin E but the benefits of supplementation at levels above those currently recommended were not established.     

Urea and trimethylamine oxide in diets for seawater farmed rainbow trout: effect on fat belching,skin vesicle,winter ulcer and quality grading

Three experiments were conducted in order to evaluate the effects of urea and trimethylamine oxide (TMAO) supplementation in diets for seawater‐farmed rainbow trout Oncorhynchus mykiss. In all experiments, commercial extruded feed was used as basal control diet, whereas experimental diets were the basal diet supplemented with either 10 g kg^–1 TMAO, 10 g kg^–1 urea or 10 g kg^–1 TMAO and 10 g kg^–1 urea. The experiments were conducted both in research units and in a commercial fish farm. Quality was evaluated in three different commercial slaughterhouses, sorting the rainbow trout into superior, ordinary or processing grade. Significantly more TMAO was observed in muscle of rainbow trout given dietary supplementation of TMAO. However, the levels were low compared with levels in marine fish in general. Trimethylamine (TMA) was not found. No increase in muscle urea content was observed in trout fed urea in the diet. Significantly reduced fat belching, seen as reduced number of fat droplets surfacing in the net pen, was observed in groups given TMAO‐supplemented feeds. At least twice as many rainbow trout with skin vesicles were observed in the control group as in the group fed urea‐supplemented diet. In addition, skin vesicles developed into open sores in the winter only in rainbow trout fed control diet. In a large‐scale trial, quality grading of almost 200 000 market‐sized rainbow trout showed significantly more (88 vs. 83%) trout of superior grade in the group fed dietary urea compared with fish fed control diet. The main reason for downgrading from superior to ordinary and processing grade was skin lesions, supporting the observations made in the experimental units.     

Effects of various dietary factors on astaxanthin absorption in Atlantic salmon (Salmo salar)

The experiment was designed to investigate the dietary factors that might enhance or interfere with astaxanthin (Ax) absorption in salmon including potentially interfering factors such as certain carotenoids (zeaxanthin and lutein), plant sterols, fibre and enhancing compounds such as cholesterol and vitamin E. Two hundred and eighty‐eight salmon (778 ± 78 g) were reared in sea water under controlled conditions and fed practical experimental diets. The experimental diets were supplemented with 40 mg Ax kg^?1, in addition to various dietary factors, including cholesterol (2%), vitamin E (450 IU kg^?1), wheat bran (5%), lutein (40 mg kg^?1), zeaxanthin (40 mg kg^?1) and phytosterol (2%). After 26 days of feeding, blood was collected and plasma was separated to determine the plasma Ax concentration. Ax was not detected in the plasma of fish fed the non‐pigmented diet. Fish fed diet containing 2% cholesterol significantly improved Ax absorption, which was reflected in the higher Ax concentration in plasma of Atlantic salmon. Other supplements including vitamin E, wheat bran, lutein, zeaxanthin and phytosterols in diet had no significant effect on plasma Ax concentration . Fish fed diet containing 2% cholesterol significantly increased cholesterol concentration in fish plasma. Phytosterol had no benefit to lower cholesterol plasma level in fish fed 2% phytosterol‐supplemented diet.     

Effects of conventional versus organic production systems on amino acid profiles and heavy metal concentrations in the Chinese shrimp <Emphasis Type="Italic">Penaeus chinensis</Emphasis>

Amino acid composition and heavy metal concentration were examined in organic and conventional Chinese shrimp Penaeus chinensis production systems during the production cycle. The crude protein and total amino acid contents for organic shrimp samples were 0.932 and 0.945 mg/g d.w., while they were 0.849 and 0.826 mg/g d.w., respectively, for conventionally produced samples. The ratios of essential amino acids to nonessential amino acids in organic and conventional cultured shrimp were 0.58 and 0.63, respectively. Shrimp samples from the conventional system were significantly richer in Cu (2.28 vs. 1.53 mg kg⁻¹), Pb (0.13 vs. 0.08 mg kg⁻¹), Cd (0.09 vs. 0.04 mg kg⁻¹), and Zn (9.94 vs. 8.42 mg kg⁻¹) when compared with those obtained from the organic system. It is concluded that organic shrimp production systems can produce comparable growth and nutritional quality benefits.