Diets For Rainbow Trout Research Articles

Postprandial kinetics of gene expression of proteins involved in the digestive process in rainbow trout (O. mykiss) and impact of diet composition.

The impact of increased incorporation of plant ingredients on diets for rainbow trout was evaluated in terms of gene expression of gastric (gastric lipase, pepsinogen) and intestinal (prolidase, maltase, phospholipase A2) digestive enzymes and nutrient transporters (peptide and glucose transporters), as well as of postprandial levels of plasma glucose, triglycerides and total free amino acids. For that purpose, trout alevins were fed from the start of exogenous feeding one of three different experimental diets: a diet rich in fish meal and fish oil (FM-FO), a plant-based diet (noFM-noFO) totally free from fish meal and fish oil, but containing plant ingredients and a Mixed diet (Mixed) intermediate between the FM-FO and noFM-noFO diets. After 16months of rearing, all fish were left unfed for 72h and then given a single meal to satiation. Blood, stomach and anterior intestine were sampled before the meal and at 2, 6 and 12 h after this meal. The postprandial kinetics of gene expression of gastric and intestinal digestive enzymes and nutrient transporters were then followed in trout fed the FM-FO diet. The postprandial profiles showed that the expression of almost all genes studied was stimulated by the presence of nutrients in the digestive tract of trout, but the timing (appearance of peaks) varied between genes. Based on these data, we have focused on the molecular response to dietary factors in the stomach and the intestine at 6 and 12h after feeding, respectively. The reduction in FM and FO levels of dietary incorporation induced a significant decrease in the gene expression of gastric lipase, GLUT2 and PEPT1. The plasma glucose and triglycerides levels were also reduced in trout fed the noFM-noFO diet. Consequently, the present study suggests a decrease in digestive capacities in trout fed a diet rich in plant ingredients.

Citric acid substituted the inclusion of inorganic phosphorus in diet of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effects of citric acid (CA) supplementation in diet without inorganic phosphorus (P) on growth, muscle and bone composition, proteolytic activities and serum antioxidant property of rainbow trout. Six diets were designed as the negative diet without monocalcium phosphate (MCP) supplementation, the positive diet containing 10 g kg−1 MCP and CA supplementation diets with 4, 8, 12, 16 g kg−1 CA supplementation in negative diet, and then were fed to rainbow trout (113.6 g) for 60 days. Results showed that the fish fed 8 g kg−1 CA, 12 g kg−1 CA diet had higher weight gain, higher contents of crude ash and P in bone, and lower feed conversion ratio than those of fish fed negative diet (P < 0.05), and showed the similar levels as those of fish fed positive diet (P > 0.05). The proximate composition and P level of muscle were not affected by dietary CA and MCP. The proteolytic activity in intestine, but not in stomach and gastric digesta, was significantly improved by dietary CA and MCP (P < 0.05), when compared with negative control. The activities of serum superoxide dismutase of 12 g kg−1 CA and 10 g kg−1 MCP groups were significantly higher, and the malondialdehyde of 8 g kg−1 CA and 12 CA g kg−1 groups were significantly lower than those of negative control (P < 0.05). The above results indicated that the supplementation of CA could substitute the inclusion of MCP in rainbow trout diet and the supplementation level was suggested to be 8–12 g kg−1.

The Effect of Replacing Fish Meal in the Diet with Enzyme-Treated Soybean Meal (HP310) on Growth and Body Composition of Rainbow Trout Fry.

The potential of enzyme-treated soybean meal powder (HP310) as fish meal alternative in diets for rainbow trout weighing 1.17 ± 0.3 g was evaluated for 60 days. Fish meal was replaced with HP310 at 25%, 50%, 75% and 100% of experimental diets. A control group was also considered. The results showed that diets containing 75% and 100% HP310 had significantly higher feed conversion ratio and lower feed intake, weight gain and specific growth rate compared to fish feed diets containing higher levels of fish protein ingredients (p < 0.05). Results suggested use of 50% HP310 in trout diet had a positive effect on growth performance (p < 0.05). All fish feed diets with HP310 had lower hematocrit, hemoglobin and red blood cells compared to the control group, but the differences between the control and the other treatments up to 75% HP310 replacement levels of diet (p > 0.05). However increasing in level of HP310 in the diet caused a significant increase of the white blood cells (p < 0.05). The fish fed with a diet totally replaced by HP310 showed the highest values of ash and moisture content among the diets and showed significantly different levels when compared with the control and other feeding treatments (p < 0.05).

Effects of low inclusion levels of dried drumstick tree Moringa oleifera leaves into the diets of rainbow trout, Oncorhynchus mykiss, on growth, feed conversion and some blood parameters

Effects of low inclusion levels of dried drumstick tree Moringa oleifera leaves into the diets of rainbow trout, Oncorhynchus mykiss, on growth, feed conversion and some blood parameters

Growth performance, proximate and histological analysis of rainbow trout fed diets containing Camelina sativa seeds, meal (high-oil and solvent-extracted) and oil

Two 112-day feeding trials were conducted to examine the effects of including camelina (Camelina sativa) products in rainbow trout diets. In the first experiment, 20 tanks (40L) of rainbow trout (Oncorhynchus mykiss; 2.36±0.18g, 30 fish/tank) were fed one of five diets containing solvent-extracted camelina meal (SECM) at dietary inclusion levels of 0, 50, 100, 150 or 200g/kg. Weight gain and specific growth rate (SGR) of fish fed 200g/kg SECM were significantly lower than those fed 0 and 50g/kg SECM. The protein efficiency ratio (PER) of fish fed 50g/kg SECM (2.4) was significantly higher than fish fed 0, 150 and 200g/kg SECM (all 2.1). There were no significant differences among treatments for total feed consumption or FCR, although during earlier periods of the trial, fish fed 150 and 200g/kg SECM had higher FCR than fish fed 0 and 50g/kg SECM (P<0.05). In the second experiment, 24 tanks (40L) of rainbow trout (1.0±0.1g, 30 fish/tank) were fed one of eight diets: a control diet; six diets containing full-fat camelina seed or high oil residue camelina meal (HORM), at dietary inclusion levels of 100, 200 and 300g/kg; or a diet that contained 100g/kg SECM and 151g/kg camelina oil (SECM+CO), with no added fish oil. After 112days on feed, fish fed diet containing 300g/kg camelina seed and 300g/kg HORM gained less weight than fish fed the control diet (P<0.05). Fish that consumed 300g/kg camelina seed also gained significantly less weight than fish fed 100g/kg camelina seed and 100g/kg HORM. Feed consumption was not affected by diet. FCR was higher in fish fed 300g/kg HORM than in fish fed 100g/kg camelina seed and the PER of the fish fed 300g/kg HORM was lower than that of fish fed 100g/kg camelina seed and HORM (P<0.05). There was no treatment effect on the intestinal histology of fish fed these diets (P<0.05). Fish fed up to 100g/kg SECM, camelina seed and HORM, as well as the SECM+CO diet did not perform any differently than fish fed the control diet (P>0.05). Although there were a few negative effects on performance in fish fed 200g/kg camelina seed and HORM early in the trial, this did not remain consistent for the entire trial. The maximum dietary inclusion threshold of these camelina products in juvenile rainbow trout diets is likely between 100 and 200g/kg, although further research will be required to determine more definite values. Statement of relevanceThis study determines the feed intake and growth response of rainbow trout fed camelina seed (dietary inclusion levels of 0, 100, 200 and 300g/kg), high oil residue camelina meal (dietary inclusion levels of 0, 100, 200 and 300g/kg) and solvent-extracted camelina meal (dietary inclusion levels of 0, 50, 100, 150 and 200g/kg) and a combination of 100g/kg solvent-extracted camelina meal and 151g/kg camelina oil, as well as information regarding the carcass composition and intestinal morphology of fish fed the first two ingredients. This research provides data that will enable the formulation of practical diets using these feed ingredients.

Acid and re-esterified rapeseed oils as alternative vegetable oils for rainbow trout diets: Effects on lipid digestibility and growth

The present study aimed at evaluating the effects of dietary acid and re-esterified rapeseed oils as alternatives to native vegetable oils (VO) on growth performance and feed utilization in rainbow trout. Acid oils are a free fatty acid (FFA)-rich by-product from the refining of VO and re-esterified oils are the final product of a chemical esterification process between acid oils and glycerol. Because re-esterified oils have a high content of mono- and di-acylglycerols (MAG and DAG), known for being good emulsifiers, a higher nutritive value than that of the native and the acid oils might be expected. A 72-day feeding trial where triplicate groups of rainbow trout were fed eight experimental diets formulated to contain 15% of a native, a re-esterified and an acid rapeseed oil, in addition to a 5% of fish oil (FO), was carried out. Diets with the native or the re-esterified oils blended with the acid oil were also studied. A commercial fish oil was used for the control diet. Fish fed rapeseed acid and re-esterified oil diets (RA and RE, respectively) showed high fat and total fatty acid apparent digestibility coefficients (ADC) (RA: 90.5±0.3%, RE: 92.5±1.0% for total fat and RA: 95.7±0.1%, RE: 95.8±0.2% for total fatty acids). However, the lowest total fatty acid ADC was that obtained in animals fed RA, which was significantly lower (P<0.05) than that of fish fed the rapeseed native oil diet (RN: 96.7±0.1%). No significant differences in final weight were obtained between fish fed RA (375.9±2.9g) and RE (381.5±11.1g) and those fed RN (393.7±6.1g), even though both values were significantly lower (P<0.05) than that of fish fed the control diet (411.1±3.3g). Nonetheless, fish fed diets including blends of the rapeseed acid and the re-esterified oils (RE/RA and RA/RE) had higher final weights (392.8±4.4 and 394.6±1.6, respectively) than those of RA and RE, although differences were not statistically significant. Furthermore, RA and RE diets did not produce relevant changes in plasma parameters or in the morphology of liver and intestine of fish. Therefore, the inclusion of rapeseed acid and re-esterified oils along with a 5% of FO in aqua feeds does not seem to have negative effects on fat and fatty acid digestibility, growth, plasma parameter or morphology of liver and intestine in rainbow trout. However, before recommending their use, further studies regarding their effects on the final composition and quality of fillets should be carried out. Statement of relevanceRe-esterified and acid rapeseed oils could be included in diets for rainbow trout as economically advantageous sources with no negative results in fat and fatty acid digestibility, plasma parameters and morphology of liver and intestine.

Phytase and sodium diformate supplementation in a plant-based diet improves protein and mineral utilization in rainbow trout (Oncorhynchus mykiss)

A basal isonitrogenous and isoenergetic plant-based diet (Control) was supplemented with either 10 g kg−1 sodium diformate (NaDF), 4000 FTU kg−1 phytase (Phy) or a combination of both additives (NaDF + Phy). Three hundred juvenile rainbow trout with an average weight of 120 g were randomly distributed into 12 fibreglass tanks (300 L). After 65 days of trial, fish fed diets containing phytase, NaDF or the combination of both additives showed a higher growth rate (P < 0.05) compared to fish fed Control diet. NaDF increased feed intake (P = 0.032), while phytase inclusion resulted in a better feed conversion ratio (P < 0.0001) and a higher N retention efficiency (P = 0.02) compared with the Control. Apparent digestibility of P, Ca, Mg and Zn was improved by the use of phytase (P < 0.005) as well as P, Ca and Mg retention efficiency in fish (P < 0.0001). Using 4000 FTU kg−1 phytase in plant-based diets resulted in a 13% and 50% reduction in N and P loadings, respectively. The use of NaDF in combination with phytase in a plant-based diet for rainbow trout resulted in a higher weight gain than that when NaDF was used alone.

Rainbow Trout diets and macroinvertebrates assemblages responses from watersheds dominated by native and exotic plantations

Over the past few decades, land-use changes through conversion of global forest cover to exotic plantations is contributing to both habitat and biodiversity loss and species extinctions. To better understand human influences on ecosystem, we use diet composition from introduced Rainbow Trout Oncorhynchus mykiss as indicator of potential changes in the composition of stream-macroinvertebrates due to land use changes from native to exotic vegetation (eucalyptus plantations) in southern Chile. Water quality variables, aquatic macroinvertebrates and Rainbow Trout diet were studied in 12 sites from mountain streams located in two watersheds including one dominated by native riparian vegetation and the other dominated by exotic vegetation. As expected, richness and abundance of macroinvertebrates were clearly higher at sites in native forest than in those with exotic vegetation. Collector-gatherer was the most abundant functional feeding group, but there was no statistical difference in the functional composition between the two watersheds. Differences in in-stream macroinvertebrate availability was more higher correlated with changes in Rainbow Trout diets. Specifically, taxa consumed from the watershed dominated by native forests was higher than from the watershed with exotic vegetation. Additional environmental variables showed statistical differences between watersheds. The exotic vegetation sites had the highest concentrations of dissolved solids, suspended solids, nitrates, chlorides and sulphates. Our findings show that macroinvertebrate assemblage structure and trout diets can be altered by changes in riparian vegetation. The absence of specific macroinvertebrate taxa in streams with exotic vegetation was captured by the composition of trout diets. This suggest that Rainbow Trout diets can be a good biological indicator of land use practices and thus, diet can be used as a rapid and effective tool for evaluate environmental quality. Our findings provide insights about the design of aquatic monitoring programmes to improve detection of anthropogenic impacts in streams in South America and elsewhere.

The Effect of a Mycotoxin Deactivation Product on Growth of Juvenile Rainbow Trout Fed Distillers Dried Grains

AbstractDistillers dried grains (DDG) with solubles (DDGS) is a product that has shown potential as a protein source for some fish species, but high inclusion rates of DDGS have not always been successfully achieved for Rainbow Trout Oncorhynchus mykiss. Our objective was to determine whether inclusion of a mycotoxin deactivation product (Biofix Plus) could improve the ability of high‐protein DDG (HPDDG) to replace a portion of the fish meal in diets for Rainbow Trout. The 2 × 2 factorial feeding trial examined protein source (menhaden fish meal [MFM] or HPDDG) with or without Biofix Plus. A control diet (42% digestible protein, 20% crude lipid, 25% MFM) was compared to a test diet in which HPDDG replaced 12% of the total MFM on a digestible‐protein basis (24% HPDDG inclusion). Diets were fed to juvenile Rainbow Trout (initial weight: mean ± SE = 30.5 ± 1.6 g) in four replicate tanks per treatment for 9 weeks in a 15°C recirculating system. At the conclusion of the feeding trial, we observed no negative effects of fish meal replacement on growth or feed conversion ratio; no benefit of Biofix Plus supplementation was observed. These data indicate that when Rainbow Trout diets containing a high‐quality DDGS product are balanced for digestible protein, lysine, methionine, and threonine, dietary fish meal levels can be successfully reduced to 13% without compromising growth and without the need for mycotoxin deactivator inclusion.

Refining Inclusion Levels of Grain Distiller's Dried Yeast in Commercial‐type and Plant‐based Diets for Juvenile Rainbow Trout, Oncorhynchus mykiss

AbstractRecent studies with rainbow trout, Oncorhynchus mykiss, demonstrated that grain distiller's dried yeast (GDDY) at up to 12% inclusion was an effective dietary protein source when replacing fish meal. To examine the effectiveness of GDDY when replacing an increased variety of dietary protein sources, two feeding trials were conducted. In the first trial, six commercial‐type diets were formulated to contain 42% digestible protein and 20% crude lipid with GDDY included at 0, 6, 9, 12, 15, and 18% to replace all dietary protein sources except fish meal. In the second trial, four plant‐based diets with GDDY at 0, 9, 12, and 15% were examined. Experimental diets were fed twice daily, to apparent satiation, to three replicate tanks of fish/diet (initial weight = 22.3 ± 0.7 g) for 10 wk in a 15 C recirculating system. Results demonstrated excellent fish growth and the inclusion rate of GDDY did not negatively affect growth or feed conversion. No significant negative effects of GDDY on body indices or whole‐body proximate composition were observed. Based on these results, GDDY can be included in both commercial‐type diets and plant‐based diets for rainbow trout at up to 18 or 15%, respectively, without decreasing growth performance.

Dietary effects of Spirulina platensis on hematological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study evaluated the effects of diets containing 0, 2.5, 5, 7.5 and 10% of Spirulina platensis on hematological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss). Fish (n=180; 101±8g) were randomly divided into fifteen 300L fiberglass tanks in triplicates for a period of ten weeks. The RBC, WBC, hemoglobin, total protein and albumin levels increased significantly in the groups supplemented with S. platensis. Dietary inclusion of S. platensis had no significant effects on hematocrit, cholesterol, triglyceride and lactate of the blood. HDL-cholesterol was larger in rainbow trout fed 10% S. platensis in comparison with the other diets, whereas LDL-cholesterol significantly decreased with increasing of S. platensis inclusion. Cortisol and glucose significantly decreased with increasing of S. platensis inclusion. The present results demonstrate that inclusion of 10% S. platensis can be introduced as an immunostimulant in rainbow trout diets.

Evaluation of safflower meal as a protein source in diets of rainbow trout [Oncorhynchus mykiss,Walbaum, 1792)

The effects of different levels of safflower meal (a residue of the plant oil extraction process) in diets of rainbow trout (Oncorhynchus mykiss) on growth performance, nutrient digestibility and body composition were investigated. Four different diets containing 0% (Control group), 10% (Diet 1), 15% (Diet 2) and 20% (Diet 3) safflower meal were formulated for the fish with a mean weight of 132.70 ± 0.75 g fed for 70 days. At the end of the experiment, there were no significant differences among dietary treatments for weight gain, specific growth rate and feed conversion ratio (P > 0.05). There were also no differences in the digestibility of crude protein and crude lipid between groups (P > 0.05). Supplementation of safflower meal in the diets also had no adverse effects on body composition. The results indicate that safflower meal is a promising feed ingredient and can be used up to a concentration of 20% in the rainbow trout diet with no adverse effects on growth performance, nutrient digestibility or body composition.

Feed technological and nutritional properties of hydrolyzed wheat gluten when used as a main source of protein in extruded diets for rainbow trout (Oncorhynchus mykiss)

Abstract Four diets with hydrolyzed wheat gluten (HWG) replacing graded amounts of crude protein (CP) (0, 12.5, 25, 50%) from LT fishmeal (FM) were extruded. For the diets with 0–25% replacement of FM, durable and sinking pellets were produced by adding 19–20% water in the extruder, at a constant feeding rate. The die pressure, specific mechanical energy (SME) and torque decreased with increasing HWG incorporation during extrusion of the diets with 0–25% replacement. Diametric expansion increased with increasing HWG inclusion. In uncoated pellets, sinking rate in water as well as lipid loss increased with increasing HWG. Diametric expansion increased by lipid coating. In coated pellets, water stability decreased with increasing HWG. The visco-elastic properties of the HWG prevented transport through the extruder with 19–20% water added in the barrel at 50% replacement, and water addition was reduced to 11% in order to obtain stable material flow. This diet had notably reduced die pressure, and increased SME. Diametric expansion and oil retaining capacity were low, while durability was high in uncoated pellets. Diametric expansion and water stability were reduced compared to the pellets produced with 19–20% water, while the pellets sank faster. Each diet was fed to duplicate groups of 0.4 kg rainbow trout for 56 days. The fish nearly doubled their weight, and no significant diet effects were seen on feed intake or growth. All diets resulted in feed conversion ratios (FCR) near 0.8 g dry matter intake per g gain. The apparent digestibilities (AD, %) of nitrogen, total and individual amino acids were high for all diets. AD of protein, cyst(e)in and phenylalanine significantly improved with increasing inclusion of HWG, while AD of isoleucine decreased. In conclusion, HWG had a strong effect on extrusion parameters and physical quality, and had nutritional value similar to LT fish meal when supplemented with essential amino acids. Statement of relevance The current research will help salmonid feed companies to optimally utilize a novel plant protein feed ingredient with high nutritional value and strong physio-chemical properties. This will both facilitate reduced use of fish meal, and increased use of other feed ingredients requiring increased binding. The current research also shows that HWG results in decreased SME, potentially decreasing production cost of extruded fish meal.

Restricted process water limits starch gelatinization, and reduces digestibility of starch, lipid, and energy in extruded rainbow trout (Oncorhynchus mykiss) diets

Abstract Five diets were produced with crude protein (CP) from hydrolysed wheat gluten (HWG) replacing graded (0, 12.5, 25, 50, 75%) amounts of CP from LT fish meal. Diets with 0–25% of CP from HWG were extruded with 19–20% water added in the extruder. Water addition was limited to 11% of the extrudate for the 50% HWG diet, and no water was added to the diet with 75% CP from HWG in order to obtain even flow of material in the extruder. Based on the degree of starch gelatinization (DG), estimated by differential scanning calorimetry (DSC), the diets with 19–20% process water were characterized by high gelatinization (HG), medium DG was obtained by limiting water addition to 11% (MG), and low gelatinization (LG) was the result of extruding without water added. Each diet was fed to two groups of rainbow trout in freshwater, and feces were obtained by abdominal stripping. Yttrium oxide (Y 2 O 3 ) was used as inert marker. The average apparent digestibility of starch ranged from 97 to 99% in the HG group, to 76% in the MG group, and 52% in the LG group. The AD of starch increased linearly (R 2 = 0.99) with increasing water addition in the extruder. The AD of lipid was reduced in MG and LG groups, and there was a linear (R 2 = 0.87) relationship between AD of starch and AD of lipid. As a consequence of AD of starch being quantitatively more influenced by water supplementation in the extruder than the AD of lipid, the regression of water supplementation on AD of energy was best explained (R 2 = 0.99) by a 2nd degree polynomial function, in which both the 1st and 2nd degree components were > 0. The findings emphasize the necessity of using sufficient process water during extrusion of salmonid diets both to ensure efficient digestion of starch and lipid. Statement of relevance This paper will increase the awareness in the feed industries of the necessity to secure complete gelatinization in extruded diets, since it is of high importance for digestible energy in the feed.

Iodine enrichment of rainbow trout flesh by dietary supplementation with the red seaweed Gracilaria vermiculophylla

Abstract The effects of different dietary inclusion levels (0, 5 and 10%) of IMTA-cultivated Gracilaria vermiculophylla on rainbow trout growth performance and flesh quality traits were evaluated. Flesh chemical composition (moisture, protein, lipid, vitamin E and iodine contents), sensory attributes and instrumental color were determined after a feeding period of 91 days with the experimental diets. The antioxidant activity of muscle carotenoids and hydrolysates was also determined by the 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. By the end of the experiment, fish fed CTRL or G5 diet reached similar body weight (215–220 g), but fish fed G10 weighed significantly less (167 g). Seaweed inclusion increased flesh moisture and decreased lipid content, with significant differences between the G5 and CTRL groups. Vitamin E content varied among treatments with CTRL fed fish presenting the highest levels of α-tocopherol. Iodine levels in the flesh increased with the seaweed inclusion, with fish fed G5 doubling its iodine content (214.5 μg/kg) in relation to the CTRL (111.7 μg/kg). Instrumental color showed that cooked fillets from fish fed seaweed-rich diets were more luminous (L*), less yellowish (b*) and more reddish (a*) than the CTRL. The sensory evaluation showed that fish fed with seaweed had juicier fillets than the CTRL with G5 presenting the most intense (pinkish) color. The instrumental differences are balanced in such a way that the sensory panel perceived G5 as the sample with higher color intensity. Muscle carotenoid extracts presented no significant antioxidant activity through the ABTS and DPPH assays, whereas muscle hydrolysates showed similar antioxidant activity in all dietary treatments (ca. 33% through DPPH assay). The inclusion of Gracilaria sp. meal in diets for rainbow trout seems to be possible for up to 5%, as higher inclusion levels resulted in significantly smaller fish. The sensory panel perceived G5 as the sample with higher color intensity and juicier than the CTRL. Moreover, flesh iodine content doubled in fish fed G5, confirming seaweed as a natural and effective tool to increase the nutritional value of rainbow trout. Statement of relevance/impact of your paper to the general field of commercial aquaculture This paper is relevant for the aquafeed industry and fish consumers. Fish meal has traditionally been the major dietary protein source for fish, but its reduction in aquafeeds is now a priority goal for the further expansion and sustainability of farmed fish production. Seaweeds may act as nutrient supply in fish, which in turn could ultimately function as vehicle of valuable compounds in human nutrition. This paper shows that 5% Gracilaria sp. meal can be a natural and effective tool to increase the nutritional value of rainbow trout flesh without impacting growth.

The effect of dietary n-3/n-6 polyunsaturated fatty acid ratio on salmonid alphavirus subtype 1 (SAV-1) replication in tissues of experimentally infected rainbow trout (Oncorhynchus mykiss)

Salmon pancreas disease (SPD) is one of the most commercially significant viral diseases of farmed Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in Europe. In this study, the potential for dietary mitigation of the disease using different polyunsaturated fatty acid (PUFA) profiles was assessed in rainbow trout. We experimentally infected fish with salmonid alphavirus subtype 1 (SAV-1), the causative agent of SPD. These fish were fed two diets with different n-3/n-6 PUFA ratio (high omega 3, 3.08, and high omega 6, 0.87). We assessed the influence of the diets on the fatty acid composition of the heart at 0 days post infection (d.p.i.) (after 4 weeks of feeding the experimental diets prior to SAV-1 infection), and sampled infected and control fish at 5, 15 and 30d.p.i. Viral E1 and E2 glycoprotein genes were quantified by two absolute real-time PCRs in all the organs sampled, and significantly lower levels of the virus were evident in the organs of fish fed with high omega 6. Characteristic pathological lesions were identified in infected fish as early as 5d.p.i., with no significant differences in the pathology lesion scores between the two dietary regimes. This study shows that decreasing the n-3/n-6 PUFA ratio in experimental diets of rainbow trout changes the fatty acid content of the fish, and is associated with reduced SAV-1 replication in rainbow trout.

Dietary inclusion of IMTA-cultivated Gracilaria vermiculophylla in rainbow trout (Oncorhynchus mykiss) diets: effects on growth, intestinal morphology, tissue pigmentation, and immunological response

Dietary inclusion of IMTA-cultivated Gracilaria vermiculophylla was evaluated in rainbow trout. Growth and feed efficiency were determined in fish fed 0 % (CTRL), 5 % (G5), and 10 % (G10) of the red seaweed for 91 days. Carotenoid concentration (skin and muscle), immunological parameters, and intestinal morphology were also evaluated. G10 group showed the lowest final body weight, with feed and protein efficiency ratios being significantly lower than the CTRL. Although protein intake was similar among groups, G10 diet induced the lowest protein retention and gain probably due to its smallest intestine diameter and lowest villi height. Fish fed G10 diet displayed higher carotenoid content in the skin (16.7 μg g−1) when compared with the CTRL group, but a lower concentration was registered in the flesh (0.23 μg g−1). Instrumental color showed that fillets were more luminous (L*), less yellowish (b*), and more reddish (a*) with seaweed inclusion and the lowest chrome intensity (C*) in the G10 group confirmed the lowest muscle carotenoid content in these fish. G5 diet enhanced the innate immune response of rainbow trout inducing the highest peroxidase, alternative complement (ACH50), and lysozyme activities. The inclusion of Gracilaria meal in diets for rainbow trout is possible up to 5 %, but a higher inclusion level impairs growth.

Vegetable re-esterified oils in diets for rainbow trout: Effects on fatty acid digestibility

The present study aimed at determining the effect of re-esterified oils with different monoacylglycerol (MAG) content, produced from two different vegetable sources with different degrees of saturation, palm and rapeseed, on fatty acid digestibility in rainbow trout. Re-esterified oils were obtained from a chemical esterification process using acid oils (free fatty acids (FFA)-rich by-products from the refining of vegetable oils) and glycerol (by-product of biodiesel production). This process, which produces the formation of triacylglycerols (TAG), reduces the content of FFA present in the acid oil and generates a redistribution of the fatty acids in the glycerol molecule. This redistribution could increase the amount of saturated fatty acids (SFA) located at the sn-2 position of acylglycerols. Moreover, it allows obtaining fats with a certain proportion of MAG, known for being good emulsifiers. Therefore, a higher nutritive value of re-esterified oils than that of acid oils might be expected. A 21-day feeding trial where triplicate groups of rainbow trout were fed nine experimental diets formulated to contain a 21% of different experimental oils was carried out. For each source, four different types of oil were used: native, re-esterified low in MAG, re-esterified high in MAG and acid. A commercial fish oil was used for the control diet. Although re-esterified oils had better apparent digestibility coefficients (ADC) of SFA than their corresponding acid oil diets, no improvement in SFA digestibility was observed in rainbow trout fed re-esterified oils diets compared to those fed native oil diets, not even when a high content of MAG was present. Although this improvement did not occur, both palm and rapeseed re-esterified oils could be incorporated as a fat source in diets for rainbow trout without negatively affecting fatty acid digestibility values. The study concluded that fatty acid digestibility in the experimental oils was more affected by their degree of saturation than by their positional distribution and lipid class composition of the oils.

Effect of Dietary Safflower and Canola Oil on Growth Performance, Body, and Fatty Acid Composition of Rainbow Trout (Oncorhynchus mykiss)

The objective of the present study was to evaluate the effects of the diets enriched with safflower and canola oil on growth, feed utilization, body composition, liver, and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss). Rainbow trout having approximate initial weight of 97.03 ± 0.10 g were fed the experimental diets containing only fish oil (Group 0SFO), safflower oil (50% safflower oil, Group 50SFO and 33% safflower oil, Group 33SFO), and vegetable oil blend (33% safflower and 33% canola oil, Group 66SFCO) for 45 days. Twenty-five fish were randomly assigned for triplicate treatments and offered the test diets two times daily to apparent satiation. At the end of the experiment, survival was 100% in all treatments. No significant differences in the weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio were found between fish fed with the different experimental diets. The highest hepatosomatic index (HIS) and viscerasomatic index (VSI) was obtained in 50SFO and 33SFO groups, respectively. The moisture, protein, lipid, and ash content in the body composition of the fish increased in all experimental groups. The lipid content was not significantly different among the groups (p > 0.05); however, there was a significant difference in ash content between the control and the other groups (p < 0.05). The experimental diets containing vegetable oil (50SFO and 33SFO groups) and vegetable oil blend (66SFCO group) had significantly higher concentrations of n-6 fatty acids, predominantly in the form of linoleic acid (LA). The n-3 fatty acids were present in significantly higher concentration in the control treatment (0SFO). The fatty acid composition of fish fillet and liver were reflective of the dietary lipid source. While the fillet and liver of fish fed the 50SFO diet was high in linoleic acid (18:2 n-6), fish fed the 66SFCO diet had high concentrations of oleic acid (OA; 18:1 n-9). The present study suggests that fish oil can be replaced by up to 50% with safflower oil and by up to 66% with safflower + canola oil blend in rainbow trout diets with no significant effect on growth.

Diet of the exotic Rainbow Trout in the critical habitat of the threatened Hooded Grebe

The lakes of the basaltic plateaus of Patagonia represent the only reproductive habitat for the critically endangered Hooded Grebe (Podiceps gallardoi ). More than 50 of these naturally fishless lakes have been stocked with the exotic Rainbow Trout (Oncorhynchus mykiss ). While the available information suggests that the diet composition of trout and Hooded Grebes could overlap, to date no formal studies of the diet of Rainbow Trout in these aquatic environments have been published. We characterized the diet of trout in one of the primary reproductive areas of the Hooded Grebe based on the analysis of the gut contents of 177 individuals, from 9 lakes. Amphipods were clearly the most dominant group of prey, quantified as frequency of occurrence and proportion by weight. The condition factor of trout and the abundance of amphipods in the stomach contents showed a functional relationship, suggesting that the wellness of trout depends on the availability of this prey. Amphipods also represent a primary prey for the Hooded Grebe, suggesting a strong dietary overlap with the trout. The presence of trout may generate processes of competition that could affect the survival of the Hooded Grebe. This interaction may be particularly relevant in large vegetated lakes, where the Hooded Grebe reproduces.