Effects of diludine supplementation on growth performance,liver antioxidant enzyme activities and muscular trace elements of rainbow trout (Oncorhynchus mykiss) juveniles at a low water temperature

Diludine is used as an effective agent reducing mutagenic effects of environmental pollutants, increasing productivity and protecting reproductive system of parental individuals and quality of their offspring. A 10‐week study was conducted to evaluate potential effects of diludine on rainbow trout (Oncorhynchus mykiss) juveniles growth performance, feed utilization, survival rate, liver antioxidant enzyme activities (superoxide dismutase, SOD, EC1.15.1.1 ; catalase, CAT, EC1.11.1.16 ; glutathione peroxidase, GPx, EC 1.11.1.9 ; glutathione reductase, GR, EC1.6.4.2 ; glucose‐6‐phosphate dehydrogenase, G6PD, EC1.1.1.49 and glutathione S‐transferase, GST, EC1.5.1.18 ), the levels of malondialdehyde (MDA) as a lipid peroxidation marker and muscular trace elements at a low water temperature (9 °C). Diludine was added at 0.2, 0.5 and 1 g kg^?1 to a fish meal–based control diet, and each diet was fed to triplicate groups of rainbow trout juveniles. After 10 weeks, there were no differences in survival rate between fish fed experimental diets (P > 0.05). It was observed that a significant improvability existed for both growth and feed utilization in fish fed diets supplemented with diludine (P < 0.05). Antioxidant enzymes showed significantly increased activity in liver tissues (P < 0.05) and then a decrease to initial activity levels during the experimental time. (GPx activity was not determined in the juvenile livers.) SOD and GST activities in liver of fish fed the diets with diludine tended to be higher and GR activity tended to be lower than that in fish fed the basal diet. However, in general, it was determined that different concentration of diludine did not affect the studied antioxidant enzyme activities except G6PD in the liver of juveniles fed the diet with 1 g kg^?1 diludine. On the other hand, the significant reduction was found in MDA levels in the fish fed the diets with diludine compared with basal diet on the 14th and 28th days of experiment. It was also observed that Cu, Fe, Mg, Zn and Se levels were significantly higher in the juveniles fed the diet with 1 g kg^?1 diludine than those fed the basal diet. In conclusion, the results of this trial indicate that 1 g kg^?1 dietary supplementation with diludine seems to be most positive for rainbow trout production in cold‐water adaptation.     

Evaluation of fish-meal free diets for rainbow trout, Oncorhynchus mykiss

Eight experimental diets were formulated for rainbow trout using agricultural byproducts as major ingredients. Each experimental diet contained varying amounts of corn grain, corn gluten meal, corn gluten feed and one of the following: 200 g kg^?1 peanut meal, 200 or 400 g kg^?1 soybean meal (SBM), 390 g kg^?1 low-allergen soy flour, 310 g kg^?1 soy protein concentrate, 300 g kg^?1 low-allergen soy protein concentrate or 200 g kg^?1 SBM + 110 g kg^?1 blood meal. One diet contained 200 g kg^?1 SBM and canola oil as the main lipid source. The remaining diets contained 95 g kg^?1 menhaden oil. Fish fed a commercial trout diet exhibited significantly greater weight gain (322%), and a lower feed conversion ratio (0.89) but significantly lower protein efficiency ratio (2.18) than fish fed the experimental diets. Within the experimental diets, fish fed the 400 g kg^?1 soy flour diet and the 400 g kg^?1 soybean meal diet had significantly higher weight gains (276% and 268%) and protein efficiency ratios (2.58 and 2.52), and lower feed conversion ratios (1.02 and 1.03) than fish fed other experimental diets. Fillet flavour varied between treatments. Most notable was the lower fishy flavour and higher chicken flavour of fish fed the diet that contained canola oil rather than menhaden oil. Microscopic evaluation of the liver and five sections of the gastrointestinal tract failed to demonstrate any differences between treatment groups. The ingredient costs of several experimental diets were lower than the estimated cost of a standard commercial trout diet. However, the superior feed conversion ratios of fish fed the control diet resulted in lower feed costs per unit of fish produced.     

Optimizing zinc supplementation levels of rainbow trout (Oncorhynchus mykiss) fed practical type fishmeal‐ and plant‐based diets

Rainbow trout (23.1 ± 0.4 g) were fed either a fishmeal‐ or plant‐based diet supplemented with various levels of zinc (0, 15, 30, 60 or 120 mg kg^?1) for 12 weeks. Trout fed the fishmeal diet had significantly higher weight gain than with the plant‐based diet. Zinc supplementation in the fishmeal diet had no effect on growth performance, suggesting that additional dietary supplementation of zinc is not required. However, in trout fed the plant‐based diet, growth increased significantly up to 30 mg kg^?1 zinc after which growth was not affected. Trout fed the plant‐based diet containing no zinc exhibited severe growth retardation, and in fish fed the 0 and 15 mg kg^?1 zinc diets, cataracts were present. Use of broken‐line quadratic modelling suggests that dietary supplementation of zinc needed to prevent deficiency and promote adequate growth in rainbow trout fed the plant‐based diet in this study was 30.1 mg kg^?1 (80 mg kg^?1 total dietary zinc). This is higher than the NRC (2011, Nutrient Requirements of Fish and Shrimp) dietary recommended level of 15 mg kg^?1 for rainbow trout. Following the NRC recommendation could lead to zinc deficiency in rainbow trout fed a plant‐based diet.     

Dietary yeast culture supplementation improves initial rearing of McConaughy strain rainbow trout

The addition of a yeast culture food supplement (DVAqua from Diamond V. Mills, Cedar Rapids, IA, USA) was evaluated during feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Two trials were run consecutively, starting with initial feeding, and were replicated over 2 years. The yeast culture was added to commercial trout starter at levels of 0.125 and 0.25 g kg^?1. The number of rainbow trout that died during the first 4 weeks of rearing was significantly reduced in the tanks receiving either of the yeast culture‐supplemented diets compared with the tanks receiving a control starter diet. Ending tank weights and gain were significantly and consistently greater in the tanks fed the 0.25 g kg^?1 yeast culture diet. Individual fish weights were also significantly heavier in the fish‐fed yeast culture containing diets in each year of the study at the end of 27 days. In the trials from 4 to 8 weeks postinitial feeding, mortality rates were significantly less only in the tanks receiving 0.25 g kg^?1 yeast culture supplementation. Individual fish lengths and weights at the end of the second trial were significantly greater in the tanks receiving either level of yeast culture compared with the control diet only in 1 year. Total tank weights and feed conversion were not significantly different between any of the treatments. The inclusion of DVAqua yeast culture provided significant increases in trout survival and growth through the first 4 weeks of feeding, with continued benefits for the next 4 weeks.     

A comparison of the growth performance of rainbow trout (Oncorhynchus mykiss) when fed soybean,narrow‐leaf or yellow lupin meals in extruded diets

This study compared the effect of increasing dietary inclusion of soybean, narrow‐leaf lupin or yellow lupin kernel meals when fed to rainbow trout. Each meal was formulated into a test diet to create a series of inclusion levels of 0, 100, 200, 300 and 400 g kg^?1. Each diet was formulated to the same digestible protein and energy specifications. The diets were fed to apparent satiety to 30.0 ± 0.71 g rainbow trout for 28 days. After this period, fish in the reference (0 g kg^?1) treatment attained a weight of 93.2 g. Growth of the fish among the treatments was observed to be improved by the addition of either variety of lupin meal. In contrast, growth of fish fed the soybean meal was equivalent to that of the 0 g kg^?1 fish meal reference, but was poorer at the 400 g kg^?1 inclusion level. Feed intake with the lupin meals was marginally improved with lupin inclusion, but at the higher soybean meal inclusions, feed intake was reduced relative to the fish meal reference diet. The inclusion of the different grains also had significant effects on the physical properties of the pellets.     

Transfer of toxaphene and chlordane into farmed rainbow trout, Oncorhynchus mykiss (Walbaum) via feed

The study was carried out to quantitate the transfer of toxaphene and chlordane compounds from commercial fish feed into the edible part of rainbow trout, Oncorhynchus mykiss (Walbaum) under normal rearing conditions. Trout were fed with unspiked high energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of trout increased from 10 g to more than 2092 g, reaching sizes of 51 cm length. Considerable amounts of toxaphene and chlordane residues were transferred from fish feed into trout muscle. Toxaphene concentrations increased up to 8.6 µg (Σ toxaphene indicator compounds 1–3) kg^?1 wet weight (w.w.) and chlordane reached 5.3 µg Σoxy‐, trans‐, cis‐chlordane + t‐nonachlor kg^?1 w.w. Results are also discussed on the contaminant levels based on the fat content and the effect of sexual maturation is considered in this study. The data allow the establishment of transfer rates for toxaphene and chlordane congeners from high energy diet into the edible part of farmed rainbow trout.     

Transfer of PCDDs and PCDFs into the edible parts of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), via feed

This study was carried out to quantify the transfer of polychlorinated dibenzo‐p‐dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from commercial fish feed into the edible part of rainbow trout (Oncorhynchus mykiss, Walbaum) under normal rearing conditions. Trout were fed with high‐energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of the fish increased from 10 g to more than 2092 g, reaching a size of up to 51‐cm length (Tl). Considerable amounts of PCDDs and PCDFs were transferred from the fish feed into the tissue of the trout. Dioxin concentrations increased during the time of feeding from 0.054 up to 0.914 ng WHO‐PCDD/F‐TEQs kg^?1 wet weight and from 4.991 to 15.815 ng WHO‐PCDD/F‐TEQs kg^?1 fat. A correlation was found between the dioxin concentration of the feed and the resulting concentration in the fat of the muscle tissue. The data allow the establishment of transfer rates from a high‐energy diet to farmed rainbow trout.     

Supplementation of plant‐based diets for rainbow trout (Oncorhynchus mykiss) with macro‐minerals and inositol

Replacement of fish meal with plant products in aquafeeds results in the elimination of dietary compounds which may be important for optimal growth and physiology. A study was conducted to determine if supplementation with macro‐minerals and/or inositol would improve performance of rainbow trout (Oncorhynchus mykiss) fed a plant‐based diet. Four iso‐caloric and iso‐nitrogenous diets (40 g kg^?1 protein and 15 g kg^?1 lipid) were formulated and consisted of a fish meal‐based control diet (control) and three plant‐based experimental diets. Plant‐based diets were supplemented with either macro‐minerals and inositol (+MM+I), no macro‐minerals with inositol (?MM+I), and no macro‐minerals and no inositol (?MM?I). Sodium chloride, potassium chloride and magnesium oxide were the sources used in the macro‐mineral premix. There was no effect of diet on survival, but there was an effect of diet on weight gain, FCR, feed intake, HSI and nutrient retentions. Significant liver pathology was observed in trout fed plant‐based diets without MM supplementation. Supplementation of MM and inositol significantly improved weight gain of trout fed a plant‐based diet. Supplementation of MM and/or inositol also improved PRE and ERE. This study demonstrates the importance of supplementing these nutrients to trout fed fish meal free diets.     

Top-spraying soybean meal-based diets with phytase improves protein and mineral digestibilities but not lysine utilization in rainbow trout, Oncorhynchus mykiss (Walbaum)

Two digestibility trials and two growth trials were carried out to evaluate the influence of top‐sprayed phytase on apparent digestibility coefficients (ADCs) of protein and mineral and utilization in rainbow trout fed with soybean meal‐based diets. In Trial 1, a semi‐purified diet containing 50% soybean meal was supplemented with graded levels of phytase (0, 500, 1000, 2000 and 4000 U kg^?1 diet), and fed to triplicate groups of fish. In Trial 2, commercial‐type extruded feeds containing 36% soybean meal with either 0 or 2000 U phytase kg^?1 were fed to five replicate groups of fish. Phytase clearly decreased phytic acid content of feces from 35 to 5 mg and from 34 to 14 mg phytic acid per g faecal dry matter in Trials 1 and 2 respectively. Apparent digestibility coefficient of P improved from 23% to 83% in Trial 1 and from 35% to 54% in Trial 2 by phytase. Apparent protein increased by 1.2% and 3.2%‐units by phytase in Trials 1 and 2. Zinc digestibility was significantly increased in Trial 1, but not in Trial 2. Trials 3 and 4 were conducted to evaluate the influence of phytase on dietary P (Trial 3) and lysine (Trial 4) utilization. Three diets were prepared for each trial: P (Trial 3)‐ or lysine (Trial 4)‐deficient basal diets, basal diets with phytase supplementation (2000 U kg^?1) and P (Trial 3)‐ or lysine (Trial 4)‐fortified diets. Rainbow trout (initial weight 20 g) were fed for 10 weeks using four and six replicates for Trials 3 and 4 respectively. Phytase increased P utilization in Trial 3 as demonstrated by an increase in vertebra ash from 24.1% to 45.4%, and by an increase in weight gain from 243% to 459% of the initial weight. Phytase did not increase lysine utilization, since neither protein retention nor weight gain were enhanced by phytase. Supplemental lysine increased protein retention and weight gain to 43.1% and 514%, respectively, and also decreased whole‐body lipid contents significantly from 120 to 123 g kg^?1 in fish fed the basal diet and phytase‐supplemented diet to 106 g kg^?1 in fish fed with lysine‐fortified diet.     

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.     

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.     

Evaluation of Experimental and Practical Diets for Bluegill Lepomis macrochirus and Hybrid Bluegill L. cyanellus × L. macrochirus

Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.     

Partial replacement of fish oil by soybean oil on lipid distribution and liver histology in European sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss) juveniles

A 12‐week feeding trial was conducted to evaluate the effects of fish oil replacement by soybean oil, on lipid distribution and liver histology of two commercially important finfish species: rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax). Sea bass (16.2 ± 0.5 g; mean ± SD) and rainbow trout (52.1 ± 0.5 g) juveniles were fed one of three isonitrogenous (500 g kg^?1 CP) and isoenergetic (19 kJ g^?1) diets, containing 0% (control, diet A), 25% (diet B) and 50% (diet C) soybean oil. At the end of the experiment, lipid deposition was evaluated in muscle, liver and viscera. Cholesterol and triglycerides levels were also determined in plasma. Tissue total, neutral and polar lipid composition (g kg^?1 total lipids) showed no significant differences within species, regardless the dietary treatment. The same trend was observed for plasma parameters (P > 0.05). Viscera were the preferential tissue of lipid deposition, with 252–276 and 469–513 g kg^?1 total lipid content in trout and sea bass, respectively. Dietary fish oil replacement had no effect on either hepatic lipid droplets accumulation or degree and pattern of vacuolization in the observed liver sections. These data suggest that both sea bass and trout can be fed diets containing up to 50% soybean oil without adverse effects on tissue lipid composition or liver histology.     

Growth performance,nutrient digestibility and lipase activity in juvenile rainbow trout (Oncorhynchus mykiss) fed fat powder in diet containing emulsifiers (cholic acid and Tween‐80)

This research was conducted to investigate the effects of two dietary emulsifiers on nutrient digestibility and lipase activity in rainbow trout (Onchorhyncus mykiss). A basal rainbow trout diet containing fat powder supplemented with 10 and 5 g kg^?1 of cholic acid, and 20 and 40 g kg^?1 of Tween‐80. Control diet contained no emulsifiers with fat powder was replaced by fish oil. Each diet was randomly assigned to 1,500‐L tanks in triplicate. Juvenile rainbow trout with an initial weight of 27.32 ± 2.03 g were randomly distributed in the experimental tanks. The results showed that growth parameters did not change by the addition of the two emulsifiers (p > .05). Total triglyceride content was significantly higher in control fish fed diet containing fish oil (p < .05), while serum cholesterol content showed no significant differences among treatments (p > .05). Control diet resulted in a higher fat digestibility than those of other experimental diets. However, protein and ash digestibilities in diet containing emulsifier were higher than those of the control diet. Control group showed the lowest lipase activity, whereas 20 g kg^?1 Tween‐80 diet caused the highest lipase activity among treatments (p < .05). In conclusion, it seems that a higher lipase activity induced by the emulsifiers could not compensate for the negative impacts of fat powder on the experimental diets.     

Preliminary study on effects of methionine hydroxy analog and taurine supplementation in a soy protein concentrate‐based diet on the biological performance and amino acid composition of rainbow trout [Oncorhynchus mykiss (Walbaum)]

A feeding trial was conducted on the effects of methionine hydroxy analog (MHA) and taurine supplementation in diets with high levels of soy protein concentrate (SPC) on the growth performance and amino acid composition of rainbow trout, Oncorhynchus mykiss (Walbaum) comparing with fish meal based diet. The control diet had 520 g kg^?1 fish meal. In the methionine deficient diets (5.1 g kg^?1), fish meal was replaced by 490 g kg^?1 of the SPC in the SPC49 diet. The SPC49 diet was supplemented with either MHA (6 g kg^?1) only or a combination of MHA and taurine (2 g kg^?1). Fish were fed isoproteic (460 g kg^?1) and isolipidic (130 g kg^?1) diets for 12 weeks. Growth performance (i.e. weight, feed conversion ratio, and thermal‐unit growth coefficient) was inferior in fish fed the SPC49 diet. MHA supplementation improved growth performance (P < 0.05). No difference was observed when taurine was added to the SPC49 and MHA diet (P > 0.05). Whole‐body taurine contents increased with taurine supplementation, whereas plasma methionine increased with MHA supplementation (P < 0.05). In conclusion, the substitution of fish meal with SPC supplemented with MHA did not negatively impact growth, and the addition of taurine did not improve growth performance in rainbow trout.     

Partial or total replacement of fishmeal by solvent-extracted cottonseed meal in diets for juvenile rainbow trout (Oncorhynchus mykiss)

The effect of solvent‐extracted cottonseed meal (SCSM) as a partial or total replacement of fishmeal was studied in juvenile rainbow trout (Oncorhynchus mykiss). Six experimental diets SCSM0, SCSM25, SCSM50, SCSM75, SCSM75A and SCSMT, containing a gradient of SCSM 0, 152, 305, 465, 460 and 610 g kg^?1 to replace 0, 112.5, 225, 337.5, 337.5 and 450 g kg^?1 fishmeal protein were fed to triplicate groups (initial body weight of 39.2 ± 0.1 g) for 8 weeks. The diet SCSM75A was supplemented with lysine and methionine, to be similar to SCSM0 for juvenile rainbow trout. Faeces were colleted after 4 weeks of normal feeding for apparent digestibility coefficients (ADC) of dry matter, crude protein and gross energy determination. Total replacement of fishmeal adversely affected growth performance. Fish fed with diet SCSMT had significantly (P < 0.05) lower weight gain, specific growth ratio, feed conversion efficiency (FCE) and protein efficiency ratio than fish fed with other diets. The FCE of SCSM75 and SCSM75A were significantly lower (P < 0.05) than those of fish fed with SCSM0 diets. The ADC of the dry matter of SCSM75 and SCSMT were significantly lower than the SCSM0 diet, and the ADC of crude protein and the energy of SCSMT were the lowest (P < 0.05). The ADC of threonine, proline, alanine, valine, isoleucine, leucine, lysine and methionine of fish fed with diet SCSMT were lower. Lysine and methionine supplement positively affected the ADC of SCS75A diet. There were no significant differences in the fish body composition. It is shown that SCSM can be utilized in the juvenile rainbow trout diet up to 305 g kg^?1, to replace about 50% of fishmeal protein in this experiment.     

The effect of total replacement of fish oil with DHA‐Gold® and plant oils on growth and fillet quality of rainbow trout (Oncorhynchus mykiss) fed a plant‐based diet

This study investigated the effect of the replacement of fish oil (FO) with DHA‐Gold (DHA‐G)‐supplemented plant oils (PO) in rainbow trout fed plant‐protein‐based diets. Five diets (450 mg g^?1 digestible protein and 150 mg g^?1 crude lipid) were fed to rainbow trout (initial weight 37 ± 0.5 g) for 12 weeks in a 15 °C recirculating water system. The lipid inclusion types and levels were FO, PO and PO with DHA‐G supplemented at 30 mg g^?1, 60 mg g^?1 or 90 mg g^?1 of the diet replacement for corn oil. Fish fed 90 mg g^?1 DHA‐G were significantly larger and consumed more feed than fish‐fed PO or FO (218 g and 2.6% bwd^?1 versus 181 g and 2.4% and 190 g and 2.3%, respectively). Feed conversion ratio was significantly increased in fish fed 90 mg g^?1 DHA‐G (0.99) as compared to fish‐fed FO (0.90) and 30 mg g^?1 DHA‐G (0.91). Panellists found trout fillets from fish fed the 90 mg g^?1 DHA‐G diet to have significantly fishier aroma and flavour than fish fed the FO diet. Fatty acid analysis demonstrated that 60 mg g^?1 or 90 mg g^?1 DHA‐G supplementation increased PO fed fish fillet DHA to fatty acid levels equivalent or higher than those fish fed a FO diet.     

Effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides

An experiment was conducted to investigate the effect of dietary iron supplement on growth, haematology and microelements of juvenile grouper, Epinephelus coioides. Casein–gelatine‐based diets supplemented with 0, 50, 100, 150, 200 and 250 mg kg⁻¹ iron from ferrous sulphate were fed to grouper (mean initial weight: 21.0 ± 0.2 g) for 8 weeks. Weight gain was highest in fish fed the diet supplemented with 100 mg kg⁻¹ iron, intermediate in fish fed diets with 50, 150, 200 and 250 mg kg⁻¹ iron and lowest in fish fed the basal diet. Feed efficiency followed a similar trend except that the lowest value was in fish fed the basal diet and the diet supplemented with 250 mg kg⁻¹ iron. Hepatic iron was highest in fish fed diets supplemented with iron ≥100 mg kg⁻¹, followed by fish fed diet with 50 mg kg⁻¹ iron and lowest in fish fed the basal diet. The whole‐body iron was lowest in fish fed the basal diet but not significantly different from other groups, as judged by anova . Iron supplement to the basal diet had no significant effect on haematological parameters (red blood cell count, haematocrit and haemoglobin), hepatic copper concentration or manganese, zinc concentration in liver and whole body. Broken‐line analysis of hepatic iron indicated that iron supplementation of 100 mg kg⁻¹ satisfied the hepatic iron storage and that further supplementation did not expand the iron status.     

Supplementation of maca (Lepidium meyenii) tuber meal in diets improves growth rate and survival of rainbow trout Oncorhynchus mykiss (Walbaum) alevins and juveniles

Maca tuber meal is used in fish diet formulations in Andean trout culture and knowledge of its effects on fish growth is paramount to healthy human food production. In the first experiment with rainbow trout alevins (0.096±0.002 g), starter diets were offered from first feeding until 15 weeks. We formulated high protein content (～60%) semi‐purified starter diets supplemented with 0%, 5%, 10%, or 15% maca tuber meal (control, M‐5, M‐10, and M‐15 respectively). The second feeding trial was conducted with juveniles (1.56±0.02 g) fed one of three diets (control, M‐15, and commercial) for 8 weeks. In the first experiment, fish fed M‐10 and M‐15 diets exhibited significantly higher growth rates than the other dietary groups. Survival was significantly improved in the groups fed diets supplemented with maca tuber meal (60.0–69.2%) in comparison with the group fed a control diet (21.7%). The second experiment showed a higher growth rate in the M‐15 group compared with the control and a commercial diet fed group. Leucocyte numbers were increased by dietary supplementation of maca tuber meal. The findings of the present study suggest that a maca tuber meal inclusion at least 5% improves growth rate, feed utilization, immunity by increased leucocyte number, and survival of rainbow trout alevins and juveniles.     

Quantifying the dietary niacin requirement of the Indian catfish, Heteropneustes fossilis (Bloch), fingerlings

A growth study was conducted to determine the dietary niacin requirement of the Indian catfish, Heteropneustes fossilis (Bloch), fingerlings (Mean weight 9.41 ± 0.18 g). Semi‐purified diets with five levels (0, 5, 10, 20 and 40 mg kg^?1 diet) of supplemental niacin were fed to H. fossilis for 15 weeks. Each diet was fed to three replicate groups of fish. Results indicated that the highest (P < 0.05) weight gain was for the fish fed the diet supplemented with 20 mg niacin kg^?1, followed by fish fed the diets with 40, 10 and 5 mg niacin kg^?1, and the lowest in fish fed the unsupplemented control diet. Patterns of specific growth rate (SGR) and protein efficiency ratio (PER) were similar to those of the weight gain. Survival of fish fed the control diet and niacin‐supplemented diet was 58% and 91–100% respectively. Niacin deficiency signs such as anaemia, anorexia, lethargy and skin haemorrhage were observed in fish fed the control diet. The haematocrit values (Ht) were higher (P < 0.05) in fish fed the diets supplemented with niacin than in fish fed the control diet. The hepatosomatic indexes (HSI) of fish fed with or without niacin‐supplemented diets were not significantly (P > 0.05) different from each other. Both body protein and lipid content were higher (P < 0.05) in fish fed the diet supplemented with 20 and 40 mg niacin kg^?1, respectively, than those fish fed other diets. The niacin content in liver significantly (P < 0.05) reflected the supplementation level in the diet and ranged from 29.11 to 40.31 mg g^?1 tissue. The associated liver niacin content for growth was about 47 μg g^?1 tissue. Quadratic regression analysis showed that the dietary niacin requirement for maximal growth of H. fossilis under these experimental conditions was about 25 mg kg^?1 diet.