Diets For Rainbow Trout Research Articles

Use of corn distiller’s dried grains with solubles as a feed ingredient for rainbow trout (Oncorhynchus mykiss) feeds: Growth, digestibility, liver and intestine histology

A feeding trial was performed to investigate the effects of the partial replacement of fish meal with distiller’s dried grains with solubles (DDGS) on growth, feed assessment, economic assessment, digestibility of diets, as well as liver and intestinal histology of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous and isocaloric diets were prepared using DDGS in rates of 0%, 10%, 20% and 30% (Control, DDGS10, DDGS20, and DDGS30, respectively) instead of reducing the fish meal content. Triplicate groups of 25 rainbow trout (mean initial weight 19.88±0.02 g) were fed with the diets for 84 days. The results revealed that dietary DDGS30 had the highest final weight and specific growth rate. Feed conversion and protein efficiency rates were similar among the dietary treatments. Economic conversion ratio was reduced depending on DDGS increase in diet that resulted in an increased economic profit index. The apparent digestibility of the diets did not differ significantly among treatments. There were no significant differences in the diameter of hepatocyte nuclei but there was a detected amount of vacuolization in the hepatocyte cytoplasm of fish fed the dietary DDGS20 and DDGS30 diets. Distal intestine histomorphometric parameters were unaffected by dietary treatments, however, increased lamina propria width was observed as the rate of DDGS increased in diets. These results indicate that DDGS can be added to rainbow trout diets by up to 30% without negatively affecting growth performance, diet digestibility, as well as the histology of the liver and intestine.

Apparent digestibility coefficients of brewer's by-products used in feeds for rainbow trout (Oncorhynchus mykiss) and gilthead seabream (Sparus aurata)

A trial was conducted to test the effect of partial replacement of fishmeal by two brewery industry byproducts, yeast and spent grain, included in isoproteic (41% CP) and isolipidic (22% CL) diets for gilthead sea bream (Sparus aurata) and rainbow trout (Oncorhyncus mykiss), having in mind the availability of these byproducts. A first step before an ingredient is included in a commercial feed is to evaluate the nutritional quality of these raw materials by measuring their digestibility. Thus, the apparent digestibility coefficients of the diets and ingredients were determined after a 30 days feeding trial and faecal collection. Apparent digestibility coefficients of these by products in the case of rainbow trout varied between 75 and 88% whereas for gilthead seabream was between 71 and 88%. According to the results obtained, the inclusion of 20–30% of brewers' spent yeast and spent grain in the feed for carnivorous fish either from fresh (rainbow trout) or marine (gilthead seabream) gave similar results to a feed with fish meal as the main protein source and show a good protein, lipid and amino acid digestibility. Taking into account that these by-products are produced in large quantities in Europe, they can be a potential source of protein to reduce the use of plant proteins or fish/animal byproducts (trimmings) and increase the sustainability of both sectors, brewery industry and aquaculture.

Partial replacement of wheat flour and corn meal with olive pomace in diet of rainbow trout (Oncorhynchus mykiss): effects on growth performance, body composition, hematological parameters and sensory evaluation

Partial replacement of wheat flour and corn meal with olive pomace in diet of rainbow trout (Oncorhynchus mykiss): effects on growth performance, body composition, hematological parameters and sensory evaluation

Parental Selenium Nutrition Affects the One-Carbon Metabolism and the Hepatic DNA Methylation Pattern of Rainbow Trout (Oncorhynchus mykiss) in the Progeny.

Selenium is an essential micronutrient and its metabolism is closely linked to the methionine cycle and transsulfuration pathway. The present study evaluated the effect of two different selenium supplements in the diet of rainbow trout (Onchorhynchus mykiss) broodstock on the one-carbon metabolism and the hepatic DNA methylation pattern in the progeny. Offspring of three parental groups of rainbow trout, fed either a control diet (NC, basal Se level: 0.3 mg/kg) or a diet supplemented with sodium selenite (SS, 0.8 mg Se/kg) or hydroxy-selenomethionine (SO, 0.7 mg Se/kg), were collected at swim-up fry stage. Our findings suggest that parental selenium nutrition impacted the methionine cycle with lower free methionine and S-adenosylmethionine (SAM) and higher methionine synthase (mtr) mRNA levels in both selenium-supplemented treatments. DNA methylation profiling by reduced representation bisulfite sequencing (RRBS) identified differentially methylated cytosines (DMCs) in offspring livers. These DMCs were related to 6535 differentially methylated genes in SS:NC, 6890 in SO:NC and 7428 in SO:SS, respectively. Genes with the highest methylation difference relate, among others, to the neuronal or signal transmitting and immune system which represent potential targets for future studies.

Utilization of combined extruded soybean and corn gluten meals as feed ingredients for juvenile rainbow trout,Oncorhynchus mykissdiet

In this study, feeding experiment and subsequent digestibility trial were performed to investigate the utilization of extruded soybean meal (SBM) and corn gluten meal (CGM) as feed ingredients for juvenile rainbow trout. Plant ingredients have undergone extrusion at low temperature (100°C, LT) or high temperature (150°C, HT) for 30 s. Four isonitrogenous (44%, crude protein) and isolipidic (14%, crude lipid) diets were formulated. Control diet is fishmeal based while a combined (1:1) non-extruded SBM and CGM for NE diet, LT SBM and LT CGM for LT diet and HT SBM and HT CGM for HT diet. Two hundred forty rainbow trout juveniles (7.8 g average body weight) were randomly divided into 12 rectangular 60 L glass aquaria and offered four different diets in triplicate. Fish were fed at satiation twice a day, six days a week for 12 weeks. Phosphorus in phytic acid level of extruded ingredients decreased through extrusion cooking. Final weight, weight gain, SGR and PER of fish fed HT diet were significantly (p < .05) higher than those fed with NE diet. Apparent digestibility coefficient for protein of LT and HT diets is significantly higher than of NE diet. The results of this study demonstrated that HT extruded SBM and CGM are suitable feed ingredients for rainbow trout diet without compromising fish growth, feed utilization and fish body composition.

Dietary inclusion of full-fat Hermetia illucens prepupae meal in practical diets for rainbow trout (Oncorhynchus mykiss): Lipid metabolism and fillet quality investigations

Insects are able to bio-convert organic by-products into a sustainable biomass for aquafeed formulation. Specifically, among several insect species, Hermetia illucens (H) is particularly interesting for its nutritious traits but, unfortunately, the lipidic fraction is poorly represented by polyunsaturated fatty acids n-3 and poses some limits in its application in aquafeed formulation.The present study undertook an interdisciplinary approach to explore the effects of three experimental diets containing increasing levels of full-fat H meal (H0 diet based on fishmeal and purified protein-rich vegetable ingredients; H25 and H50 diets containing 25% or 50% of full-fat H meal replacing fishmeal, respectively), on rainbow trout (Oncorhynchus mykiss) fed over a 98 days experimental period. The expression of genes related to lipid metabolism by RT-qPCR, liver histology, as well as the qualitative traits of fillets and fatty acid (FA) composition were investigated. Interestingly, fads2 gene expression in pyloric caeca increased in fish fed diets containing the highest full-fat H meal inclusion (H50 > H0; p < .05). Liver histological examinations showed normal morphological aspect even though hepatic FA profiles seemed to resemble those of the diets. However, liver docosahexaenoic acid did not significantly differ between the dietary groups and showed a mean value of 11.07 g FA methyl esters/100 g total FA methyl esters. Despite the FA profile of the three diets differed depending on the H meal inclusion level, biometrics, fillet physical traits, total lipids and the overall FA profile were not jeopardised, not even eicosapentaenoic and docosahexaenoic acids.The overall results showed that the dietary full-fat H meal inclusion under study did not impair fish fillet quality, guaranteeing its nutritional value. Some effects on lipid metabolism were observed, as suggested by liver, pyloric caeca and mid intestine gene expression and liver FA profile. Future studies on the biological mechanisms behind the macroscopic traits of fish fed unprocessed insects are warmly encouraged.

Effect of dietary n-3 series fatty acids on sperm motility duration of rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

Objective: This study was performed to determine the effect of different ratios of n-3 series fatty acids added to the diets of rainbow trout(Oncorhynchus mykiss) on sperm motility duration.Methods: A total of 48 male rainbow trouts about 3 years of age were used in the study and 4 groups were formed. The one that n-3 series fattyacids were not added to the diet was used as control group. n-3 series fatty acids were added to the experimental groups diets at the ratiosof 1% (E1), 2% (E2) and 3% (E3), respectively. Semen was collected by abdominal massage. The time-dependent sperm motility change wasdetected under the microscope at x400 magnification.Results: A significant decrease was detected in the motility only at 360th hour in E3 group compared to the control group (p&amp;lt;0.05).Conclusion: As a result, it was concluded that feeding with diets containing different ratios of n-3 series fatty acids had no effect on the motilityof rainbow trout semen under in vitro condition.

Effects of Partially Defatted Hermetia illucens Meal in Rainbow Trout Diet on Hepatic Methionine Metabolism.

Simple SummaryFor sustainable aquaculture development, fish meal from the sea in aquafeed should be replaced with other sustainable materials such as insect larvae. The authors fed black soldier fly maggot meal to rainbow trout and examined the expression of three genes and two metabolites involved in turn-over of methionine that is an essential amino acid in fish. According to the increase in the maggot content in the aquafeed, gene expression was modulated to maintain an optimal level of methionine metabolites. Dietary replacement of up to 50% of fish meal with the maggot meal was acceptable, implying future development of a new aquafeed for sustainable aquaculture.This study investigated, for the first time, the effects of replacement of fishmeal (FM) with insect meal from Hermetia illucens (HI) on the transcript levels of three genes involved in methionine (Met) metabolism in rainbow trout (Oncorhynchus mykiss) liver. Two target genes—betaine-homocysteine S-methyltransferase (BHMT) and S-adenosylhomocysteine hydrolase (SAHH)—are involved in Met resynthesis and the third one—cystathionine β synthase (CBS)—is involved in net Met loss (taurine synthesis). We also investigated the levels of two Met metabolites involved in the maintenance of methyl groups and homocysteine homeostasis in the hepatic tissue: S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). Three diets were formulated, an FM-based diet (HI0) and two diets in which 25% (HI25) and 50% (HI50) of FM was replaced with HI larvae meal. A 78-day feeding trial involved 360 rainbow trout with 178.9 ± 9.81 g initial average weight. Dietary replacement of up to 50% of FM with HI larvae meal, without any Met supplementation, did not negatively affect rainbow trout growth parameters and hepatic Met metabolism. In particular, Met availability from the insect-based diets directly modulated the transcript levels of two out of three target genes (CBS, SAHH) to maintain an optimal level of one-carbon metabolic substrates, i.e., the SAM:SAH ratio in the hepatic tissue.

Immunity and growth improvement of rainbow trout (Oncorhynchus mykiss) fed dietary nettle (Urtica dioica) against experimental challenge with Saprolegnia parasitica

In this study, effects of nettle (Urtica dioica) on growth, immunity, and gene expressions were examined in rainbow trout after an 8-week feeding period. A total of 264 juvenile rainbow trout (10.72 ± 0.55 g) were selected and stocked randomly in 12 aquaria. Nettle powder was added to the fish feed at three doses, 0.5,1 and 1.5% served as treatments. At the end of 8-week feeding period, the fish were exposed to Saprolegnia parasitica for 3 weeks. Results showed that all treatments fed with nettle diets exhibited significant increases in weight gain and SGR, and decreased FCR compared to the control. Feeding the fish with dietary nettle resulted in significant rises in blood indices and non-specific immunity in comparison with the control. Furthermore, fish fed 0.5% of dietary nettle showed significantly increased expressions of TNF-α, IL-1b, IL-6 and IL-8 genes following 8 weeks of feeding. A significant reduction in mortality rate was observed in the fish treated with 0.5% of nettle compared to the control following challenging with S. parasitica. Our observations indicate that the use of 0.5% nettle powder in rainbow trout diet can improve growth and immunity parameters as well as fish resistance against S. parasitica contamination.

Dietary inclusion of mealworm (Tenebrio molitor) meal as an alternative protein source in practical diets for rainbow trout (Oncorhynchus mykiss) fry

BackgroundAn 8-week feeding trial was designed to evaluate the potential of yellow mealworm (MW; Tenebrio molitor) as a locally available nutrient-rich feedstuff for rainbow trout fry (Oncorhynchus mykiss).MethodsTriplicate groups of fish (mean ± SE; 1.11 ± 0.01 g) were assigned to each of the five isonitrogenous and isocaloric practical diets containing graded level of a full fat MW (0, 7, 14, 21, and 28%) at the expense of fish meal (designated as MW0, MW7, MW14, MW21, and MW28, respectively).ResultsFish growth performance in terms of weight gain and specific growth rate significantly increased with increasing dietary MW level up to 14% and then declined when dietary MW levels further increased to 28%. Significantly higher protein efficiency ratio and lower feed conversion ratio were found in fish fed with diets containing MW compared to fish fed the control MW0. Myeloperoxidase activity was significantly higher in fish fed MW7 diet compared to fish fed the MW0 diet. Fish fed the MW14 and MW28 diets had significantly higher lysozyme activities than those fed the MW0 diet.ConclusionsOverall, the efficacy of MW as promising alternative to fish meal in practical diets for rainbow trout fry has been proved not only in relation to growth rates and feed utilization, but also from the viewpoint of immunopotentiation effects.

A novel marine algal oil containing both EPA and DHA is an effective source of omega‐3 fatty acids for rainbow trout (Oncorhynchus mykiss)

AbstractNovel sources of omega‐3 fatty acids (FAs) are essential for the sustainable development of the aquaculture industry. In the present study, we assessed the response of the fish to a novel algal oil as a source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for rainbow trout (Oncorhynchus mykiss) diets. Our results show that the palatability of the diets was maintained with high inclusion levels (up to 10%) of algal oil. The digestibility of omega‐3 FAs was compared among diets containing 10% fish oil (control diet) and diets with no omega‐3 lipid sources (0AO) or increasing levels of algal oil (2.5, 5, and 10% for diets 2.5AO, 5AO, and 10AO, respectively). The digestibility of EPA and DHA was above 99% and was only significantly decreased in the 0AO diet. The FA profile of the muscle was found to reflect that of the diets, suggesting that, when high levels of omega‐3 are included in the diet of rainbow trout, they are deposited in the muscle rather than used for metabolic processes. The growth and the blood parameters of the animals were optimal for all the treatments in the safety trial, with algal oil inclusion levels up to 6%. All these results in combination show that Veramaris® algal oil containing EPA and DHA can be used as an efficient source of omega‐3 FAs for salmonids.

Growth performance, plasma parameters and liver antioxidant enzymes activities of Rainbow trout (Oncorhynchus mykiss) juvenile fed on Spirulina platensis extract

The purpose of this study was to evaluate the physiological responses of Rainbow trout fed on diets supplemented with methanolic extract of Spirulina platensis. 150 fish with a mean initial weight of 12.6±0.3 g were randomly divided into five groups. The juveniles were fed for 8 weeks with the diets containing 0, 250, 500, 1000 and 2500 mg of S. platensis extract per kg of diet. After eight weeks, 12 fish from each treatment were subjected to confinement stress. It has been shown that 250 mg of the algae extract per kg of diet resulted in the highest final weight and lowest feed conversion ratio in fish. There was no significant difference between treatments in fat, protein and moisture contents. The results showed that three hours after the air exposure and confinement stress, minimum (2.42 mg dl-1) and maximum (6.18±2.5 mg dl-1) levels of plasma cortisol were observed in 2500 and 500 mg kg-1 treatments, respectively. Moreover, the minimum (66±14 mg dl-1) and maximum (168±18 mg dl-1) level of glucose has been observed in 0 and 500 mg kg-1 treatments, respectively. After eight hours, Plasma cortisol and glucose have showed the highest level in 500 mg kg-1 treatment. There was no difference in lysozyme and catalase enzyme activities, but higher Spirulina extract in diet led to an increase in superoxide dismutase enzyme activity in the liver of Rainbow trout. This study suggests that addition of 250 mg kg-1 of Spirulina extract to Rainbow trout diet can improve growth performance and stress condition.

Effects of varying dietary levels of digestible protein and digestible energy on growth performance in juvenile Yellowstone Cutthroat Trout (Oncorhynchus clarkia bouvieri)

Cutthroat trout (Oncorhynchus clarkii) are widely cultured in state and federal hatcheries and private farms throughout the Western United States for stock supplementation or recreational fisheries. Cutthroat Trout culture techniques often rely on methods borrowed from the culture of closely related Rainbow Trout (Oncorhynchus mykiss). Even though commercial feeds for Rainbow Trout are commonly utilized, these formulations are unlikely to be optimal for Cutthroat Trout growth. Therefore, in an effort to determine an optimal digestible protein to digestible energy ratio for raising Cutthroat Trout more efficiently, eight diets formulated with 4 different levels of digestible protein (DP: 32.5 %, 37 %, 41.7 % and 46 %) and 2 different levels of digestible energy (DE: 4370 kcal/kg and 4770 kcal/kg) were fed to triplicate tanks of Yellowstone Cutthroat Trout and compared with a commercial Rainbow Trout diet over a 12 week study. All test diets performed better on indices of biomass accrual than the commercially available diet. Results suggest commercially available Rainbow Trout diets are less efficient formulations for Yellowstone Cutthroat Trout and new formulations should be considered. Optimizing digestibility, protein retention, minimizing lipid accrual, and maintaining high biomass gain in tanks, leads to the conclusion that a diet representing a DP:DE of 68.4 mg kcal−1 performed best. Moreover, protein retention decreased as DP:DE increased across test diets. Retention of lipids and gross energy did not appear to be significantly altered by dietary DP or DE.

Effects of feeding with red algae (Laurencia caspica) hydroalcoholic extract on antioxidant defense, immune responses, and immune gene expression of kidney in rainbow trout (Oncorhynchus mykiss) infected with Aeromonas hydrophila

In this study, the effects of hydroalcoholic extract of red algae (Laurencia caspica) at different levels were evaluated on antioxidant defense, innate immune responses, and expression of immune genes in rainbow trout (Oncorhynchus mykiss). A total of 750 rainbow trout (39.43 ± 0.44 g) were randomly assigned to five treatments with three replicates (50 fish per replicate) in 15 ponds and reared for 8 weeks. Fish samples were fed a diet containing different levels of algal extract (0, 5, 10, 15, and 20 g extract per kg of basal diet). At the end of feeding period, the fish were challenged with Aeromonas hydrophila and fish mortality was recorded over a 10-day period. To evaluate the antioxidant and immune parameters, fish were sampled at day 0, end of weeks 4 and 8, and after bacterial challenge. Expression of immune genes (IL-1β, lysozyme II, Complement C3, and TNFα) was also examined after bacterial challenge. Results indicated that application of algal powder in fish diet improved lysozyme activity, complement system, and immunoglobulin levels of extract fed-fish compared to control group (p < .05). The activities of antioxidant enzymes (catalase, glutathione peroxidase, and superoxide dismutase) were affected by the algal extract, with increasing levels in algal extract treatments compared to control fish (p < .05). According to the results, relative expression of target genes showed significant increases in 1.5% treatment compared to the other and control groups (p < .05). At the end of 10-day fish exposure to A. hydrophila, fish survived significantly higher in treatments received the algal extract than the control group, with the highest survival rate recorded in 1.5% algal extract (p < .05). According to the effective results of L. caspica extract on stimulating the immune system and increasing fish resistance to A. hydrophila, it is recommended to use 1.5% of this algal extract in rainbow trout diets.

Use of dietary oil, solvent-extracted meal and protein concentrate from Camelina sativa for rainbow trout, Oncorhynchus mykiss, at the early fry stage

A 98-day feeding trial was conducted in a 24-tank freshwater flow-through system (13 ± 0.5 °C) to evaluate the effects of using dietary camelina oil (CO), solvent-extracted camelina meal (SECM), and camelina protein concentrate (CPC) in early fry diets for rainbow trout (initial weight 1g/fish, 50 fish/tank). Triplicate tanks were randomly fed one of eight diets including aCamelina sativafree control diet, two diets containing CO at either 50 or 100% replacement of fish oil, three diets containing 6, 12, or 18% SECM, and two diets containing 6 or 12% CPC. Dietary replacement of 100% of added fish oil with CO, and dietary inclusion of up to 18% SECM or 12% CPC did not result in significant reductions in growth and feed efficiency, or changes in proximate whole-body carcass composition and hindgut morphology of rainbow trout fry. However, fish fed diets containing 18% SECM, did require a longer acclimation period to the feed and, ultimately, gained less weight, presumably due to a poorer protein utilization efficiency in the early days of the trial.

Utilization of grape seed oil as a dietary lipid source in rainbow trout (Oncorhynchus mykiss) diets

ABSTRACT A 60-day feeding trial was conducted to determine the effects of different levels of grape seed oil (GO) on growth performance, digestive enzyme activity, fillet proximate and fatty acid composition of rainbow trout (Oncorhynchus mykiss) juveniles (40.17 ± 0.04 g). Five experimental diets were formulated where fish oil (FO) was replaced with 0 (D1), 25 (D2), 50 (D3), 75 (D4) and 100 (D5) % GO. The growth performance was significantly improved with increasing GO levels up to 50% after which fish growth declined (P < .05). Fillet fatty acid composition was showed significantly highest n-6 PUFA levels with increasing GO in diets, while n-3 HUFA levels especially EPA and DHA were significantly decreased (P < .05). Fish fed on diets containing higher levels of GO revealed a decrease in α-amylase activity, whereas trypsin, total alkaline protease, and lipase activities increased significantly with increasing GO levels up to 50% and then decreased. Based on the findings of the present study, it could be concluded that GO could be included in diets up to 50% where it had the best performance over the other diets tested in the present experiment.

Partially Defatted Tenebrio molitor Larva Meal in Diets for Grow-Out Rainbow Trout, Oncorhynchus mykiss (Walbaum): Effects on Growth Performance, Diet Digestibility and Metabolic Responses.

Simple SummaryThe current developments in the aquaculture sector have highlighted the need to find sustainable ingredients to replace fishmeal as a protein source in fish feeds. The use of insect meals may be a valid option, due to their good nutritional values and low ecological footprint. In this study, we evaluated the effects of a progressive fishmeal substitution with increasing concentrations of a partially defatted yellow mealworm meal in rainbow trout diets. We observed that the total substitution of fishmeal with insect meal is feasible and that there are no negative effects on fish growth or on the digestibility of most nutrients. The activities of hepatic enzymes involved in the amino acid metabolism and lipid synthesis were also evaluated. The enzymatic activities were not negatively influenced by insect meal inclusion in the diets. These results are of practical application for feed manufacturers and farmers, as they support the inclusion of insect meals in fish diets to obtain sustainable feeds that able to support an increase in aquaculture production.Insect meals are good candidates to replace fishmeal as new protein sources in aquafeeds. This study evaluated the effects of fishmeal replacement with different dietary inclusion levels of a partially defatted Tenebrio molitor (L.) larva meal (TM) on rainbow trout (Oncorhynchus mykiss Walbaum) growth, diet digestibility, and hepatic intermediary metabolism. A 154-day growth trial was performed with 252 rainbow trout (78.3 ± 6.24 g) randomly divided into twelve tanks and fed four experimental diets containing increasing levels of TM: 0% (TM0), 25% (TM25), 50% (TM50), and 100% (TM100) of fishmeal substitution, corresponding to TM dietary inclusion levels of 0%, 5%, 10%, and 20%, respectively. A digestibility trial was performed feeding 180 rainbow trout (94.6 ± 7.31 g) with the experimental diets used in the growth trial. The growth parameters were not affected by TM dietary inclusion. Regarding the evaluated apparent digestibility coefficients (ADC), only the ADC of crude protein was affected, showing the following trend: TM0 = TM25 > TM50 > TM100. The activities of key hepatic amino acid catabolic and lipogenic enzymes were not affected by the dietary composition. The results suggest that a partially defatted TM could totally replace fishmeal in commercial rainbow trout diets without negative effects on fish performance.

Hematological and biochemical blood indices of rainbow trout depending on the level of protein in feeds

Protein nutrition of fish is one of the main factors of ensuring their active growth. Finding the optimal concentration of protein is an actual direction of research. The purpose of the experiment was to establish the effect of different protein nutrition levels in commercial rainbow trout feeding on hematological and biochemical parameters of their blood. For this purpose, five experimental groups were formed by the method of analogs. The experiment lasted 210 days and was divided into two periods: equalization (10 days) and main (200 days). During the equalization period, the feeding ration was the same for fish in the control and experimental groups. In the main period, the level of protein in experimental feeds for different experimental trout groups ranged from 44 to 52% per 1 kg. It was found that different levels of rainbow trout’s protein nutrition did not cause significant changes in blood morphological composition. It is proved that rearing trout using compound feeds with a crude protein content of 50% and 52% promotes the increase of red blood cells, hemoglobin, white blood cells and phagocytic activity in blood. The use of 44% and 46% low crude protein diets in fish feeding reduces the morphological components in blood. As a result of studies on the phagocytic activity of neutrophils in fish blood, a slight increase was revealed under the influence of the studied factor. The analysis of the obtained results showed that with increasing levels of crude protein in the diets of rainbow trout, the concentration of total protein and its fractions in blood serum increased. Accordingly, the amount of total protein in blood of fish in the control group was 60.0 g/L, in the experimental groups – it was within the range of 59.6- 65.3 g/L. The increase in the level of rainbow trout’s protein nutrition in the experimental groups 4 and 5 caused an increase in the number of albumins, β-globulins and γ-globulins compared to control. As a result of experimental studies, an increase in the mineral status of rainbow trout blood during use of feeds with the crude protein content of 50-52 % was established. No differences were found during the assessment of trout white blood cell counts. The use of the obtained results during the production of compound feed will allow having a positive effect on the hematological parameters of commercial rainbow trout

Partial and total replacement of fish oil with fatty acid ethyl esters in the starter diets of rainbow trout (Oncorhynchus mykiss)

Fatty acid ethyl esters (FAEE) are a potential alternative to fish oil as a source of polyunsaturated fatty acids in fish feeds. This investigation examined the growth performance, lipid composition, and intestinal and liver histology of rainbow trout (Oncorhynchus mykiss) fed experimental starter diets with graded levels of FAEE and fish oil. Five experimental diets were formulated with 20% total lipid content and 0%, 25%, 50%, 75%, and 100% replacement of Alaskan Pollock oil with FAEE oil, and they were formulated with analogous fatty acid levels. The five diets used defatted fish meal as the primary protein source, and a sixth diet was included that used full-fat fish meal and extracted fish oil. Triplicate groups of rainbow trout (144 ± 20 mg initial weight) were fed experimental diets for 62 days on a restricted feeding regime (4–5.5% biomass/day). The group fed the full-fat fish meal diet had faster growth and a lower feed conversion ratio than the defatted fish meal diet groups after 31 and 62 days of feeding. The growth rate and feed conversion ratios of fish were significantly different between the FAEE-containing diet groups in the first 31 days of feeding, but were not significant from 32 to 62 days of feeding. Fatty acid analysis showed similarity between the fatty acid profiles in experimental diets and in fish muscle and liver tissues at the end of the experiment (all groups mean weight ~3.6 g/fish). Satiation feed intake for a single day was measured at 31 days of feeding, and feed intake was higher in the 100% FAEE diet than the control (8.3 ± 1.1% vs 6.4 ± 0.3% daily satiation ratio). This result suggests that FAEE has a positive effect on voluntary feed intake. Histological analysis of posterior intestine enterocytes and hepatocytes showed a significant reduction in lipid vacuole size in the 100% FAEE group, relative to the defatted and full-fat fish meal control groups. These results suggest that rainbow trout had utilized diet with ≥50% FAEE less efficiently in the first feeding phase, likely due to reduced fatty acid absorption, but that these trends were diminished as fish grew to a larger size.

Towards sustainable and ocean-friendly aquafeeds: Evaluating a fish-free feed for rainbow trout (Oncorhynchus mykiss) using three marine microalgae species

Aquaculture, the fastest growing food sector, is expected to expand to produce an additional 30 million metric tons of fish by 2030, thus filling the gap in supplies of seafood for humans. Salmonids aquaculture exploits the vast majority of fishmeal and fish oil rendered from ocean-dwelling forage fish. Most forage fish diverted to these commodities are human-food grade, and all are primary prey for marine predators. Rising costs, price volatility, and environmental sustainability concerns of using these commodities for aquaculture feed are driving the global search for alternatives, including marine microalgae originating from the base of marine food webs but produced in culture. We report the first evaluation of two marine microalgae, Nannochloropsis sp. and Isochrysis sp., for their potential to fully replace fishmeal and fish oil in diets of rainbow trout (Oncorhynchus mykiss), an important model for all salmonid aquaculture. We conducted a digestibility experiment with dried whole cells of Nannochloropsis sp. and Isochrysis sp., followed by a growth experiment using feeds with different combinations of Nannochloropsis sp., Isochrysis sp., and Schizochytrium sp. We found that digestibilities of crude protein, crude lipid, amino acids, fatty acids, omega 3 polyunsaturated fatty acids (n3 PUFA), docosahexaenoic acid (DHA), n6 (omega 6) PUFA in Isochrysis sp. were significantly higher than those in Nannochloropsis sp. Digestibility results suggest that for rainbow trout diets Isochrysis sp. is a better substitute for fishmeal and fish oil than Nannochloropsis sp. The lower feed intake by fish fed diets combining multiple microalgae, compared to fish fed the reference diet, was a primary cause of the growth retardation. In trout fillets, we detected an equal amount of DHA in fish fed fish-free diet and reference diet. This study suggests that Isochrysis sp. and Schizochytrium sp. are good candidates for DHA supplementation in trout diet formulations.