Effects of dietary inclusions of red beet and betaine on the acute stress response and muscle lipid peroxidation in rainbow trout

This study evaluates the effects of red beet (RB) and betaine on rainbow trout submitted to an acute stress challenge. A control diet was compared with four experimental diets in which red beet (14 and 28%) and betaine (0.9 and 1.63%) were incorporated in different concentrations according to a factorial design. Cortisol in plasma and fin, glucose and lactate plasma levels, and malondialdehide (MDA) in muscle were all measured before the stress challenge and 30 min and 6 and 12 h after the stress challenge as parameters to determine the diet effects. RB and betaine had no effect on cortisol, glucose, and MDA basal levels. However, lactate basal levels were significantly lower on fish fed with RB and betaine. Thirty minutes after the stress challenge, there was a significant increase in plasma and fin cortisol, glucose and lactate concentrations, although fish fed with diets containing RB and betaine showed significantly higher plasma cortisol values. MDA values of fish fed with 14% RB and 0.9% betaine were significantly higher than MDA values from fish fed with 28% RB and 1.63% betaine. After 6 and 12 h, plasma and fin cortisol and lactate levels recovered in a similar trend. Glucose plasma levels recovered in almost all groups 12 h after the stress. Also, MDA values recovered basal levels after 6 and 12 h. RB and betaine did not enhance the tolerance to the stress challenge compared to the control group, although the presence of these ingredients had no negative effect on any of the stress indicators.     

Effects on Lipid Oxidation and Bioactive Properties of Rainbow Trout Fillets Fed with Barley

Barley concentrations ranging from 0% to 32% were incorporated into rainbow trout (Oncorhynchus mykiss) diets. The effect of barley concentration on lipid peroxidation and antioxidant activity of fish fillets were analyzed. Results showed that the inclusion of barley in rainbow trout diets had an inhibitory effect on lipid oxidation, probably associated with certain bioactive compounds in barley that could interact with scavenging and reducing metabolites involved in lipid oxidation. Concentrations up to 8% of barley produced fish fillets with high antioxidant activity and higher levels of alpha-tocopherol.     

Effect of partial replacement of dietary fish meal by soybean meal with betaine attractant supplementation on growth performance and fatty acid profiles of juvenile rainbow trout (Oncorhynchus mykiss)

This study was conducted to investigate the effects of dietary incorporation of soybean meal for fish meal replacement and supplementation of betaine as an attractant on growth performance and fatty acid profiles of rainbow trout (Oncorhynchus mykiss). Juvenile trout were fed practical diets, with increasing soybean levels and betaine supplementations. The experimental diets consisted of a control diet with fish meal as the sole protein source (control) and no attractant, 25% soybean‐1% betaine diet (SBM25‐B1), 50% soybean‐2% betaine diet (SBM50‐B2), and 50% soybean‐0% betaine diet (SBM50‐B0). Average body weight was 12.69 ± 0.16 g at the beginning of experiments. Following 54 days feeding programme with experimental diets, average body weights reached 47.45 ± 1.22 g, 58.11 ± 1.77 g, 56.34 ± 1.87 g and 53.76 ± 1.74 g in the control, SBM25‐B1, SBM50‐B2 and SBM50‐B0 groups respectively. As compared with control treatment, significant differences were observed in weight gain, specific growth rate and feed intake of 1% betaine treatment at 25% soybean‐meal‐incorporated diet (p < .05), but no differences were observed in feed conversation ratio and survival rates (p > .05). Compared with the control treatment, betaine‐supplemented groups had significantly higher total saturated fatty acid contents (p < .05). On the other hand, the control treatment showed a significantly higher level of monounsaturated fatty acid than the betaine‐supplemented groups (p < .05). Significant differences were observed in fatty acid profile of 1% betaine‐supplemented group (p < .05) compared with the control. Present findings revealed that 1% betaine supplementation with dietary incorporation of soybean meal at 25% level positively influenced growth performance, feed utilization and fatty acid profiles of rainbow trout juveniles.     

Effects of Feeding High Monounsaturated Sunflower Oil Diets on Sensory Attributes of Salmonid Fillets

The purpose of this study was to determine if substituting high oleic acid sunflower oil for herring oil in formulated salmonid diets affected sensory attributes of fillets from coho salmon (Oncorhynchus kisutch) and rainbow trout (Oncorhynchus mykiss). Two feeding trials were conducted in which coho salmon and rainbow trout were fed diets containing either high oleic acid sunflower oil or herring oil as the supplemental lipid source (12.4% of the diet by weight) for 6-8 weeks. In standard directional triangle tests on previously frozen rainbow trout and coho salmon fillets stored at 5¦C for up to 10 days, a significant number of panelists were able to differentiate between fillets from the two dietary treatments based on aroma, and determined that the herring oil fillets had a ôfishierö aroma than the sunflower oil fillets. The panelists tended to prefer rainbow trout fillets from the sunflower oil treatment to fillets from the herring oil dietary treatment. These results suggest that increasing the monounsaturated fatty acid level in fish by feeding a high monounsaturated fatty acid finishing diet could potentially decrease oxidative rancidity, a major cause of quality deterioration in aquatic food products, and thereby improve the shelf life and sensory characteristics of the fillets.     

Effects of Spirulina and plant oil on the growth and lipid traits of white sturgeon (Acipenser transmontanus) fingerlings

The aim of this research was to evaluate the efficiency of diets with Spirulina and plant oils (POs) inclusion for white sturgeon weaning and their effects on the fatty acid (FA) composition of fish flesh. Three isoproteic (45%) and isoenergetic (21 MJ kg^?1 DM) diets were formulated: one fish meal‐based diet integrated with fish oil (FMO) and two 40% Spirulina meal‐based diets integrated with corn (SPC) or soybean (SPS) oils respectively. One hundred and thirty‐five white sturgeon fingerlings (mean weight 17.5 g) were stocked randomly in nine fibreglass tanks. At the end of the trial, which lasted 71 days, the growth performance traits and somatic indexes were determined. The chemical composition, gross energy and FA profile were determined on the fish fillets. No significant effects were observed for the growth performances or fillet chemical composition. The FA profile of the fillets reflected those of the diets. In particular, the fillets of the fish fed with the SPC and SPS diets were lower in n‐3 FA, due to the substitution of fish oil (FO) with POs. It is possible to replace FO and meal in sturgeon; therefore, Spirulina meal integrated with POs could be a good alternative to sturgeon diet.     

The olive oil by‐product in ‘rainbow trout Onchorynchus mykyss (Walbaum)’ farming: productive results and quality of the product

The aim of this work is to investigate olive oil by‐product [vegetation water (VW)] inclusion in rainbow trout diet and its effect on the productive traits and the quality of the product. Two levels of VW inclusion were used and one control group was included. Fish diets were isonitrogeonous (crude protein 40%) and isoenergetic (18 MJ kg^?1 DM). Two thousand and four hundred rainbow trout were used. An in vivo digestibility experiment was performed in order to determine diets’ digestibility. All the fish diets and fillets were analysed to determine the proximate and fatty acid composition. On final fish fillet, lipid oxidation was determined at 0, 24, 48, 72, 96 and 192 h of storage using the 2‐thiobarbituric acid method (thiobarbituric acid reactive substances). Aroma analyses on the final cooked and raw fillet were performed using an electronic nose. The VW inclusion partially reduced protein digestibility. The fish growth varied between 1.08% and 1.1% day. The supplemental level of VW led to a better antioxidant status of fish fillet, in particular, in the fillet sample after 72 h of fillet conservation. Principal component analysis in raw and cooked fish fillet indicates that the VW inclusion in the fish diet led to aroma modification on fish fillet.     

Partial to total replacement of fishmeal by poultry by‐product meal in diets for juvenile rainbow trout (Oncorhynchus mykiss) and their effect on fatty acids from muscle tissue and the time required to retrieve the effect

Triplicate groups of rainbow trout (Oncorhynchus mykiss) (1.4 ± 0.1 g) were fed experimental diets containing four levels of protein substitution to totally replace fishmeal with poultry by‐product meal (0, 33, 67 and 100%). Fishmeal (FM) from tuna fish by‐products and poultry by‐product meal ‘pet food grade' (PBM) were used. Diets were formulated to be isonitrogenous (43.5% crude protein) and isolipidic (12.5% crude fat). After 80 days of feeding, no significant differences were found in terms of thermal unit growth coefficient (TGC). However, the EPA levels in muscle tissue among treatments 0PBM, 24PBM and 44PBM were found to be significantly higher than those for the 59PBM diet. Nevertheless, a re‐feeding period with the control diet showed that 28 days was long enough to regain the FA profile needed. We concluded that PBM used up to 44% in diets for juvenile rainbow trout can be used without a significantly decrease in EPA and DHA under the present conditions. The use of a whole fishmeal diet could be an important strategy to recuperate the fatty acid profile obtained when trout is feed on PBM basis. It will be important to perform longer experiments with larger fish to confirm these results.     

Proximate Composition, Lipid Oxidation, and Sensory Characteristics of Fillets from Rainbow Trout Oncorhynchus mykiss Fed Diets Containing 10% to 30% Lipid

This study was conducted to determine the effects of increasing dietary lipid concentrations on fillet characteristics of post-juvenile rainbow trout. A feeding trial was conducted with fish meal based diets containing 10, 15, 20, 25, or 30% lipid for 24 wk. Menhaden oil was the lipid ingredient. Weight gain was significantly greater in fish fed the 30% lipid diet than in fish fed either 10%, 15% or 20% lipid diets. There were no significant differences in visceral somatic index. Fillet lipid concentration of fish fed the 30% lipid diet (9.2-g lipid/ 100-g fillet) was significantly higher (P < 0.05) than fish fed either the 10% or 15% lipid diets (5.8- and 6.9-g lipid/100-g fillet, respectively). In samples stored for 3 d at 5 C or S wk at -20 C, sensory panelists reported that the cooked fillets from fish fed the 30% lipid diet were "more fishy" than fish fed the 15% lipid diet, and preferred the cooked fillets from the 15% lipid treatment over the 30% lipid treatment. Triangle tests and fillet colorimetry showed no significant differences between fillets from fish fed the 15% and 30% lipid diets at any sampling time point. No significant differences in fillet concentrations of thiobarbituric reactive substances were observed among dietary treatments stored at either 5 C or -20 C. These results suggest that two main effects of feeding a 30% lipid diet (with fish oil as the lipid source) are a higher lipid concentration in the fillet and a "fishier" aroma compared to fillets from fish fed a 15% lipid diet.     

The effects of phase‐feeding rainbow trout (Oncorhynchus mykiss) with canola oil and Alaskan pollock fish oil on fillet fatty acid composition and sensory attributes

Rainbow trout (186 g) were fed three test diets where the lipid source (150 g kg^?1) was either menhaden oil (MO), pollock oil (PO) or canola oil (CO) for eight weeks to an average weight of 370 g. The CO group was then divided into two groups, one continuing on the CO diet and the other switched to the PO diet (CO–PO). After nine additional weeks of feeding, the average fish weight approximately doubled (719–749 g). No significant differences were found in average final weight or fillet yield among dietary treatment groups. Fatty acid profiles of fillets from trout fed MO, PO or CO‐supplemented diets reflected the fatty acid profiles of the added oils, whereas the fatty acid profile of fillet from trout in the CO–PO group exhibited values similar to those of fish fed PO. The ratio of ω3 : ω6 FA was nearly 2.5 times higher in fillets from the CO–PO group compared to the CO group. Sensory analysis showed that panelists preferred CO‐fed fillets over those fed MO, PO, or CO–PO. Phase‐feeding CO and PO reduced fish oil use and resulted in fillets with double the content of Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) over CO‐fed fish, similar to levels in MO‐fed fish.     

Synergic Effects of Light Salting,Vacuum Packaging,and Onion Extract on the Quality Retention of Refrigerated Rainbow Trout (Oncorhynchus mykiss) Fillets

This experiment investigated the synergistic effects of vacuum packaging, light salting, and onion extract on the shelf life of rainbow trout (Oncorhynchus mykiss) fillets stored under refrigeration. The chemical, microbial, and organoleptic changes were monitored for up to 18 days in fillets. Total volatile basic nitrogen (TVB-N) and free fatty acid (FFA) values were evident in the order: control (without salting, vacuum packaging, and extract) > air packaged, salted (APS) > vacuum packaged, salted (VPS) > and vacuum packaged, salted, containing 2% and 4% (v/w) onion extract (2% and 4% VPSOE) throughout the storage period. Thiobarbituric acid values in APS groups were higher than control groups. Data from microbial assay showed that treatment with 2% and 4% VPSOE decreased total viable microbial count (TVC) compared with other treatments. APS, VPS, and VPSOE samples remained acceptable for up to 8, 12, and 15 days, respectively. The most suitable indices for determining shelf life of rainbow trout fillets are TVC.     

Influence of nanochitosan/zeolite composite on growth performance,digestive enzymes and serum biochemical parameters in rainbow trout (Oncorhynchus mykiss)

Protective effects of nanochitosan/zeolite composite besides zeolite and chitosan/zeolite composite on rainbow trout growth, digestive enzyme activities and biochemical parameters were studied. Nanochitosan/zeolite hybrid composites with three different ratio of nanochitosan:zeolite (35:100, 3.5:100 and 0.35:100) were synthesized and analysed by X‐ray powder diffraction (XRD), thermal gravim (TG) analysis and scanning electron microscope (SEM) methods. Prepared composites as well as zeolite and control diets were fed to rainbow trout (50 g) for a period of 60 days. The addition of treated diets significantly improved growth performance compared to the control diet. Supplemental zeolite could only enhance the amylase activity in fish intestine, whereas other treatment groups could increase the pepsin activity besides intestinal alkaline phosphatase, trypsin and amylase activities. No differences were observed for intestinal acid phosphatase and lipase activities among the experimental diets. Meanwhile, serum total antioxidant activity and lipid peroxidation product, indicated by malondialdehyde (MDA), significantly increased and decreased, respectively, with some doses of administration, indicating the elevated antioxidant status in treatment groups. Serum‐specific marker enzymes, namely aspartate aminotransferase (AST) and alkaline phosphatase (ALP), were not affected in all groups. Meanwhile serum total protein in most treatment groups was significantly higher than the control group. Results showed that synthesized composites especially nanochitosan/zeolite composite at 5 g/kg had potential to enhance growth performance, digestive enzyme activities and some biochemical parameters in rainbow trout.     

Influence of bacterial protein incorporation and of sulphur amino acid supplementation to such diets on growth of rainbow trout, Salmo gairdnerii Richardson

A single cell protein (SCP) of methanophillic bacterial origin was incorporated into rainbow trout diets, at increasing levels of substitution for fish meal. Growth characteristics of rainbow trout fed these diets with or without sulphur amino acid supplementation (SAA) were followed over an experimental period of 16 weeks. It appeared from the results that this novel protein could replace nearly 80% of fish meal with no adverse effects on overall performance. Feed intake was adversely affected when the SCP was the major source of protein. Digestibility of protein was found to be increased at high levels of incorporation of the SCP.Effects of an addition of sulphur amino acids (L- or DL-methionine or L-cystine) to diets with 14% SCP or without SCP were also observed. Supplementation of these diets with the different SAA depressed trout growth to varying degrees. It was found that L-cystine had a more depressive effect than L-methionine, which in turn had a greater effect than DL-methionine. These results are discussed in the light of recent data on the SAA needs of rainbow trout. This study revealed that total substitution of fish meal in trout diets was feasible, and that there was no need for further supplementation with sulphur amino acids in the type of compounded diets used in this study.     

Effects of Dietary Protein Source and Feeding Regime on Growth Performance,Nutrient Digestibility,Fatty Acids,and Quality Characteristics of Rainbow Trout,Oncorhynchus mykiss,Fillets

This study investigated the effects of dietary protein source and feeding regime (apparent satiation and rationed) on growth performance, nutrient digestibility, fatty acid (FA) profile, and fillet quality traits in rainbow trout. A stock of 1200 juvenile trout (mean weight 114.6 ± 0.2 g) were randomly distributed into 24 fiberglass tanks (four diets × three replications × two feeding regimes). The experimental diets were formulated to be isoproteic and isoenergetic based on bacterial protein meal (BPM), pea protein concentrate (PPC), mixture thereof (MIX), and fish meal (FM), respectively. The feeding trial lasted 77 d with water temperature of 13 C. Statistical differences appeared among the diets only in terms of crude protein digestibility. Growth performance and somatic indexes were significantly affected by the diet, while only the condition factor was influenced by the feeding regime. None of the parameters appeared to be affected by the interaction effects. Differences appeared between the FA profiles of the dorsal muscle. Oleic, linoleic, α‐linolenic, and docosahexaenoic acid contents were influenced by diet, while only minor FAs were influenced by feeding regime. In conclusion, growth performance and nutrient digestibility resulted lower in fish fed BPM diet than other groups, while PPC group was similar to FM group.     

Effects of dietary supplements on the availability of minerals in fish meal; preliminary observations

Preliminary studies were conducted to determine if several feed supplements with the potential to improve dietary mineral availabilities in fish meal had any measurable effect in fish feeds. In the first study with rainbow trout, 11 supplements were tested: citric acid; sodium citrate; potassium chloride; sodium chloride; histamine dihydrochloride; EDTA disodium salt; sodium bicarbonate; a mixture of amino acids; ascorbic acid; a mixture of inositol and choline; and cholecalciferol. Apparent availability of calcium, phosphorus, magnesium, sodium, iron, manganese and strontium in fish meal-based diets was determined using both yttrium oxide (Y₂O₃) and chromium oxide (Cr₂O₃) as inert dietary markers. Apparent availability was expressed as the fractional net absorption (%) of minerals from diets. After a 7-day acclimation period with test diets, fecal samples were collected for five consecutive days using passive collection systems. Apparent availability of calcium, phosphorus, magnesium, iron, manganese and strontium was increased by citric acid supplementation. Apparent availability of manganese also was increased by EDTA and sodium citrate. The other supplements had no measurable effect on the apparent availability of minerals in fish meal. In the second study, the effect of supplemental citric acid was further investigated using monogastric (rainbow trout) and agastric fish (goldfish). Fish were fed for 5 weeks (rainbow trout) or 3 weeks (goldfish) with fish meal-based diets containing either 0% (control), 2% or 5% citric acid on a dry basis. Feces were collected by settling and by stripping. Apparent availabilities of calcium and phosphorus were greatly affected by citric acid supplementation in rainbow trout but not in goldfish. Phosphorus levels in feces of fish fed a diet with 5% citric acid were approximately half of that of fish fed the control diet (0% citric acid) in the rainbow trout trial. This pattern was consistent during the 5-week feeding trial. A dietary supplement of citric acid as high as 5% did not reduce feed intake or appetite of rainbow trout. Conversely, this level of dietary acidification led to a marked reduction of feed intake in goldfish. Dietary supplementation of citric acid at 2% level did not reduce feed intake of goldfish; however, this level of dietary acidification had little effect on the apparent availability of major minerals in fish meal-based diet. Levels of non-fecal excretion of calcium and phosphorus, inorganic phosphorus in urine, and citric acid in feces were increased in rainbow trout fed 5% citric acid. The pH values of the feces and urine were decreased in rainbow trout fed citric acid. Plasma bicarbonate, plasma calcium and phosphorus, and blood pH of rainbow trout tended to increase by a 5% dietary supplementation of citric acid. The soluble inorganic phosphorus content increased in the diets and decreased in the feces of rainbow trout by supplementing the diet with 5% citric acid. Feces samples of rainbow trout collected by stripping provided similar availability values to data collected by settling for most elements except sodium, which had negative values in all dietary treatments.     

Effects of diets containing a bacterial protein meal on growth and feed utilisation in rainbow trout (Oncorhynchus mykiss)

Triplicate groups of rainbow trout with initial weight 361 g were fed either a fish meal based control diet or diets containing 9, 18 or 27% bacterial protein meal (BPM) or 9% of an autolysate (AU) of the BPM. No significant treatment effects were found on specific growth rates (SGR), feed intake, feed efficiency ratio (FER), or retention of nitrogen, amino acids or energy. The apparent digestibility coefficients (ADC) of nitrogen, energy and most indispensable amino acids decreased when BPM was included in the diet. The ADC of lipid, sum of amino acids, arginine, lysine, threonine and most of the dispensable amino acids were reduced at 27% BPM inclusion compared to the control, 9% and 18% BPM diets. None of the ADC estimated was different in the 9% AU diet compared to the 9% BPM diet. The loss of nitrogen and energy in faeces per kg gain increased as the dietary BPM or AU levels increased, and the energy used for activity and maintenance was higher in fish fed the 27% BPM diet than in fish fed the other diets (P < 0.05). There were no significant differences in the urea concentrations in plasma, liver and muscle, whereas the uric acid level in plasma was elevated in trout fed the 27% BPM diet. Histological evaluation of tissue from the stomach, pyloric caeca, mid-intestine and distal intestine did not reveal any diet-related morphological changes.In conclusion, no significant differences in growth and feed efficiency were found in the rainbow trout fed diets containing up to 27% BPM, and the AU did not increase fish performance compared to the BPM. Based on the data from this study, at levels up to 27% dietary inclusion, BPM is a good replacement for fish meal in diets for rainbow trout.     

Response of Rainbow trout (Oncorhynchus mykiss) to unrefined peanut oil diets: Effect on growth performance,fish health and fillet fatty acid composition

A 60‐day feeding study with rainbow trout, Oncorhynchus mykiss, was conducted to determine the effects of replacement of fish oil (FO) by unrefined peanut oil (PO) on growth performance, feed utilization, body composition, fatty acid composition and serum biochemical and haematological parameters. Rainbow trouts (51.60 ± 0.75 g) were fed five experimental diets formulated by replacing dietary FO with PO at levels of level 0 (PO₀), 1/4 (PO₂₅), 1/2 (PO₅₀), 3/4 (PO₇₅) and 4/4 (PO₁₀₀), respectively. As a result, the best growth performance was observed in fish fed with PO₀ and PO₅₀ diet. No significant differences were detected among the groups in terms of body compositions. Fatty acid profiles of the fish fillets reflected the fatty acid profiles of the feeds that the fishes were fed with. In this study, the haematological parameters detected that there were no significant differences compared to the control group, whereas the serum biochemical parameters generally worsened as the ratio of peanut oil in the ration exceeded half of fish oil. As a conclusion, the results of the study suggested that the unrefined peanut oil could be used as a replacer of fish oil in diets for rainbow trout.     

Composition,Properties and Sensory Quality of Rainbow Trout Affected by Feed Formulations

Rainbow trout were fed a fish meal‐based diet or diets where 25, 50, 75, or 100% of the fish meal protein was replaced with a mixture of rendered animal protein ingredients. Diets were formulated to be iso‐nitrogenous (36% crude protein) and meet all known nutrient requirements of rainbow trout. The effect of five diets on dressing percentage, chemical composition, functional properties, and sensory characteristics of rainbow trout fillets stored up to 1 wk on ice in a refrigerated room (4 C) was determined. Dressing percentage based on body weight (from 724 to 811 g) did not show a significant difference due to the diet. Raw tissue pH, 24 and 144 h post mortem, were significantly lower than the control when 75 and 100% fish meal replacement were utilized. Assessment of color, texture, flavor, and tenderness indicated that fillet were lighter, less firm, more bland, and more tender after 144 h compared to 24‐h storage time. Fillets from fish fed all diets were considered as acceptable by the panel.     

Effects of dietary nucleotides on the antioxidant status and serum lipids of rainbow trout (Oncorhynchus mykiss)

An 8‐week feeding experiment was conducted to evaluate the effects of dietary nucleotides (0, 0.5, 1, 1.5 and 2 g kg^?1) on serum antioxidative biomarkers and lipid contents of rainbow trout fingerlings. The serum triglycerides and low‐density lipoprotein (LDL)‐C levels were significantly decreased in fish fed diets containing 1.5 and 2 g kg^?1, whereas serum high‐density lipoprotein (HDL)‐C was higher in trout receiving diets with those levels of nucleotides. A significant decrease in thiobarbituric acid reactive substances concentration was observed in groups receiving 1.5 or 2 g kg^?1 of dietary nucleotides in comparison with control group (?32% and ?27%, respectively). A significant decrease was observed in catalase and serum glutathione peroxidase activity in trout fed 1.5 and 2 g kg^?1 dietary nucleotides compare with other groups. There were no significant changes in serum superoxide dismutase activity among the experimental groups. In conclusion, these results suggest that dietary nucleotides may reduce lipid peroxidation by increasing the levels of antioxidant lipoprotein, HDL‐C, and decreasing the LDL‐C, the main substrate of lipid peroxidation.     

Growth response and fatty acid composition of rainbow trout (Oncorhynchus mykiss) fry fed diets containing different levels of soybean and egg lecithin

We investigated the effect of soybean and chicken egg lecithin on the growth performance, fatty acid profile and body composition of rainbow trout fry. Seven isonitrogenous and isolipidic diets were prepared by replacing 0, 2, 4 and 6 % soybean and egg lecithin instead of soybean oil in diets. Trout fry with initial average weight 120 ± 4.08 mg were randomly distributed in twenty-one 90-L tanks. Triplicate groups (165 fish per tank) of fry were fed to visual satiation at six meals per day for 40 days. Incorporation of 2 and 4 % egg lecithin led to increase in final weight, specific growth rate and weight gain compared with control group. Also, 4 % soybean lecithin had moderate effects on growth performance of fry. The fatty acid compositions of fry were influenced by dietary fatty acid. Fish fed egg lecithin showed higher amount of monounsaturated fatty acid than soybean lecithin and control groups. Fry fed soybean lecithin had significantly higher levels of polyunsaturated and n-6 fatty acid than egg lecithin and control groups. Soybean and egg lecithin induced higher amount of highly unsaturated fatty acid in lecithin groups compared with control group. The lipid and ash content of whole-body tissues were positively affected by percentages of soybean and egg lecithin in the diets. So 6 % soybean and egg lecithin induced higher amounts of lipid and ash body content. The results of our study indicated that dietary egg lecithin had growth-promoting effect, and rainbow trout fry had moderate lecithin requirement (at least 2 % as fed).     

Effect of dietary kefir on the growth performance,feed utilization and fatty acid profile of juvenile rainbow trout,Oncorhynchus mykiss

A study was conducted to determine the effect of feeding with diets containing kefir on growth performance and fatty acid profile of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous (450 g protein kg^?1) and isocaloric (4325 kcal kg^?1) diets were prepared in trout feed to contain 0 (control), 20, 50 and 100 g kg^?1 kefir. Fish, initial weight of 46 g, were randomly distributed into triplicate 520‐L fibreglass tanks in freshwater flow‐through system. Fish were fed at 4% of the body weight thrice a day for 12 weeks. The results indicated that survival rate ranged from 97.14 to 100% without significant difference among treatments (p > .05). Whole‐body moisture and lipid composition were significantly affected by diets containing different levels of kefir (p < .05), but no differences were determined in protein and ash. Furthermore, the fatty acid profile of flesh showed differences among the groups. The percentages of saturated fatty acid in the flesh lipid decreased, while 18:3n‐3 and polyunsaturated fatty acids were increased at higher substitution levels of kefir grain. The present study showed that up to 100 g kg^?1 supplementation of kefir in diets could be improve the fatty acid profile, especially PUFA, in fish flesh without adverse effect on the growth, feed utilization and survival rate of rainbow trout.