Trout Feed Research Articles

The use of oilseed processing products in compound feed for poultry and aquaculture

Recently, the oil processing industry has been actively developing in the Lower Volga region, the by-products of which are presscake and extracted meal. The purpose of our research was to study the infl uence of feeding local non-traditional feed sources as part of compound feed on the live weight of broiler chickens and rainbow trout. Studies on broiler chickens of the cross Ross 308 were carried out at the Research Center for the safety and eff ectiveness of feed and Additives of the Volgograd State Agrarian University. The chickens of the control group received compound feed with sunfl ower presscake, and in the diet of poultry of the 1st, 2nd and 3rd experimental groups sunfl ower presscake was replaced with amaranth presscake – 50, 75 and 100 %, respectively. Scientifi c and economic experiment on the study of the possibility of including protein concentrate Gorlinka in compound feed for rainbow trout was carried out at the enterprise SO Kalmykova I. O. The fi sh of the control group received compound feed with sunfl ower extracted meal, and individuals of the 1st, 2nd and 3rd experimental groups received compound feed, in which sunfl ower extracted meal was replaced by Gorlinka concentrate – 50, 75 and 100 %, respectively, by groups. It was concluded on the base of conducted studies that the introduction of amaranth presscake into the formula of compound feed had a positive eff ect on the meat productivity of broiler chickens of the cross Ross 308. So, during the period of the experiment the live weight of poultry was increased by 2,15–5,26 %, and the slaughter yield increased to 0,29 abs.%. The use of mustard protein-containing concentrate Gorlinka in compound feed for rainbow trout contributed to the increase in the total live weight gain by 2,83–6,93 %.

Evaluation of growth development and pigmentation of Heros severus cultured in a biofloc system with enriched pigment diets

This study aimed to evaluate the development and the increase in the skin pigmentation of the organism Heros severus cultured in a biofloc system with diets enriched with carotenoid pigments. The culture was made in 80 L water tanks with 20 juvenile organisms of H. severus; each treatment was made by duplicate. Four experimental diets were used: a) trout feed, El Pedregal®; b) TetraColor®; c) carrot and d) beetroot. The diet that obtained the highest values regarding the growth of the fish was the control diet. Regarding the coloration of the fish, the beetroot diet was the diet that presented the highest values with 9.55 μg of total carotenoids in tissue, presenting significant differences (P = 0.001) concerning the other diets, proving that a diet based on beetroot can be a good option for the culture of ornamental fish. Because it allows the organisms to have a survival rate above 90%, have similar growth to the control group, and a significant improvement in coloration, being a natural carotenoid low-cost source to improve the commercialization of organisms. Nevertheless, it did not present significant differences (P = 0.005) regarding beetroot and TetraColor® diets, while it presented significant differences with the carrot diet.

THE EFFECTIVENESS OF GROWING RAINBOW TROUT AT DIFFERENT LEVELS AND RATIOS OF LYSINE AND ARGININE IN GROWER COMPOUND FEED

The article highlights the results of the study of the influence of different levels and ratios of amino acids lysine and arginine in compound feed for commercial rainbow trout. The experiment was conducted on 6 groups of grower rainbow trout, 100 specimens in each. The fish were injected with 2.0 to 3.2% arginine against the background of lysine content in the first three groups – 2.8%, and 4–6 groups – 3.0%. The level of the studied factors was regulated by the introduction of synthetic preparations of amino acids. The ratio between arginine and lysine ranged from 0.71 to 1.14. Combined feed was distributed 2 times a day at the rate of 2% of the weight of the fish. Effective levels of lysine and arginine in compound feed for commercial trout have been experimentally established. The highest body weight and gains, the lowest feed ratio were observed when the compound feed contained 3.0% lysine and 3.2% arginine, with an arginine-lysine ratio of 1.07 : 1. For increasing the level of arginine in commercial rainbow trout compound feed from 2.0 up to 3.2% against the background of lysine content of 2.8%, an increase in body weight by 0.48 - 2.01% was noted; absolute, average daily and relative growth, respectively by 1.32 - 2.06%, 0.80 - 1.60% and 6.33 - 7.93%; feed costs decreased by 0.56 - 0.69%. An increase in the level of arginine in compound feed to 3.2% against a background of 3.0% lysine led to an increase in the body weight of trout by 1.05-2.64% (р˂0.01), absolute growth - by 1.52-3.65 % (р˂0.01), average daily increase - by 0.79 - 3.17% (р˂0.01), relative increase - by 9.77 - 21.84% (р˂0.01). Feed consumption per 1 kg of gain decreased by 0.87% at the arginine level of 3.2% and remained practically unchanged at the arginine level of 3.0%. An increase in the content of lysine in trout feed to 3.0% against the background of the basic level of arginine - 2.8% caused a slight increase in the body weight of fish - by 0.30 - 0.60%; of absolute, average daily and relative growth, respectively by 0.65; 0.80 and 1.28%. Feed costs decreased by 0.62%. No relationship was noted between the arginine-lysine ratio in compound feed and the growth indicators of rainbow trout, nor were there any antagonism phenomena between the studied amino acids.

Fatty acids of different nature differentially modulate feed intake in rainbow trout

Feed intake is subjected to a complex regulation involving a plethora of signals, among which nutrients stand as one of the most important. In mammals, the gastrointestinal tract is able to sense nutrients in the lumen, and respond with the release of signaling molecules that ultimately modulate brain circuits governing appetite, resulting in decreased/increased feeding. Whether equivalent mechanisms operate in fish remains unknown. In a recent study, we described that the gastrointestinal tract of rainbow trout contains several sensors for free fatty acids (FAs), and that the luminal presence of FAs of different length and degree of unsaturation modulates the levels of key gastrointestinal hormones involved in feed intake regulation. In this study, our aim was to characterize the impact of such a luminal presence of FAs on brain appetite-regulatory centers, as well as its effects on rainbow trout feed intake. Major results from this study demonstrated that: (i) FAs of different length and degree of unsaturation [medium-chain (MCFAs, octanoate), long-chain (LCFAs, oleate), long-chain polyunsaturated (PUFA, α-linolenate), and short-chain (SCFA, butyrate) FAs] differentially modulate feed intake levels when administered intragastrically, (ii) intragastrically-administered FAs modulate the phosphorylation status of appetite-related transcription factors, as well as mRNA levels of key appetite-regulating neuropeptides, in the hypothalamus and/or telencephalon, (iii) luminal presence of FAs results in changes in the central abundance of mRNAs encoding gastrointestinal hormone receptors, and (vi) luminal FA-derived central changes in neuropeptide mRNAs are not observed (or are lessened) in vagotomized fish. Together, these results provide comprehensive evidence in favor of a gut-brain axis in fish. In addition, we observed different responses in terms of feed intake regulation depending on the type of fatty acid administered into the lumen, which is very relevant for aquaculture considering differences in fatty acid composition in aquafeeds.

Proximate and fatty acid composition of meat from rainbow trout (Oncorhynchus mykiss W.) after dietary supplementation with black pepper (Piper nigrum L.) extract

The study was aimed at assessing the effect of dietary supplementation with black pepper (Piper nigrum) on the chemical and fatty acid composition in the meat of rainbow trout (Oncorhynchus mykiss W.), farmed in a recirculating system.
 Rainbow trout were distributed in two groups – experimental fed 1% powdered extract from black pepper (BPE) and control (C) fed without black pepper extract. After the end of the experiment, 6 fish from each group were euthanized, filleted and deboned. The 1% BPE in rainbow trout feed reduced meat water content and increased dry matter percentage and fat content. The fatty acid profile of rainbow trout meat was beneficially influenced by the dietary BPE supplement. The SFA percentage was statistically significantly decreased whereas contents of UFA, MUFA, PUFA and n-3 were considerably higher. No consistent effect was noted with respect to n-6 fatty acids. The improved PUFA/SFA and n-6/n-3 ratios in the supplemented group showed that the tested feed additive had a favourable effect on fatty acid content of rainbow trout meat. Both ratios were within the range, beneficial for human nutrition: > 0.4 and < 5, respectively.

A step towards sustainable aquaculture: Multiobjective feed formulation reduces environmental impacts at feed and farm levels for rainbow trout

Aquaculture is growing to meet the increasing demand for aquaculture products but is not free of environmental impacts. One solution is to improve how feed are formulated, limiting the environmental impact of fish production. Multiobjective (MO) formulation, which aims for a compromise between lower cost and lower environmental impacts, appears to be a promising solution to reduce the environmental footprint of aquaculture production. The objectives of this study were to design an eco-friendly trout feed (ECO-diet) using MO formulation and to compare its zootechnical and environmental performances to those of a commercial feed (C-diet) containing 16% fishmeal and 6.5% fish oil. MO formulation changed the composition of the diet greatly, which decreased environmental impacts of the feed as well as its price. It increased the number of ingredients used but reduced the use of fishmeal and fish oil by half. MO formulation also led to the elimination of soy products, faba bean, and gluten in favour of processed animal co-products that have high protein contents and low climate change impact. Rapeseed oil also disappeared from the ECO-diet due to its major contribution to land use, eutrophication, and acidification and, to a lesser extent, climate change. Overall, the ECO-diet had high digestibility, which differed little from that of the C-diet. Mean fish body weight after 12 weeks of growth did not differ significantly from that obtained with the C-diet, but analysis of fish growth curves indicated that the ECO-diet could lead to lower growth in the long term. This observation was consistent with the significantly lower feed intake in fish fed the ECO-diet. The decrease in impacts observed at the feed level was also observed at the farm level, although less so for eutrophication, non-renewable energy use, and climate change calculated per kg of body weight gain. MO formulation is a useful tool to reduce the environmental footprint of aquaculture production without compromising animal performances or necessarily increasing production cost.

Utilization of feed resources in the production of rainbow trout (Oncorhynchus mykiss) in Norway in 2020

The utilization of feed resources in Norwegian farming of Atlantic salmon has been reported for 2010, 2012, 2016 and 2020. The present paper is a corresponding documentation for farming of rainbow trout in Norway in 2020. 89,667 tonnes of rainbow trout were produced, which is 6 % of the amount of salmon produced. The 116,990 tonnes of ingredients used for feed sold as trout feed were produced from 13.4 % marine protein sources, 10.8 marine oils, 39.7 % vegetable protein sources, 19.9 % vegetable oils, 12.1 % carbohydrate sources and 3.9 % micro ingredients, which include vitamin and mineral premixes, crystalline amino acids and astaxanthin. In addition, was 0.2 %, or 257 tonnes, of single cell protein, insect meal, fermented products and microalgae used in trout feed. Norwegian fish meal and fish oil constituted 8.8 % of the ingredients, and the remaining 91.2 % were imported ingredients. The economic feed conversion factor (FCR) was 1.30, 1.21 or 1.44 if calculated from feed ingredients ‘as is’, feed ingredients on dry matter basis, or from registered traded feed, respectively. The trout retained 37 %, 43 %, 33 %, 63 % and 63 % of the feed’s dry matter, energy, protein, fat and EPA+DHA, respectively, in the whole body. In fillet, the corresponding retention values were 21 %, 25 %, 23 %, 34 % and 35 %, respectively. The feed utilization in trout was slightly overestimated because of some salmon feed used in the trout production. The feed ingredients used and the feed utilization in trout farming in 2020 were similar to the data for salmon farming, but trout is produced in a smaller quantity.

The use of white lupine in complete feed for trout

The article presents the material on the most up-to-date, the global problem of protein deficiency in complete feedback for fish. One of the ways to solve this problem may be the use of white lupine (Lupinus Albus) in the structures of feed recipes. An important condition for the successful development of fish farming and the implementation of planned products for the production of products, to ensure food safety, occupy feeding issues. The decision of this issue puts a number of tasks to ensure feedback, rational methods of production, on the basis of advanced scientific achievements that contribute to the technological, economic development of the industry. Therefore, in experienced formulations of complete feed, the main task was to replace the white most expensive protein component into Lupine, that is, fish flour. In the first experienced recipe, the amount of lupine natives was 10%, which made it possible to reduce the fisherous flour content by 7%. The second experimental recipe in its structure contained lupine white without a shell in an amount of 22%, this made it possible to reduce the content of fish flour by 14%. The third experienced rechart contained Lupine without a shell of 25%, which made it possible to reduce the content of fish flour by 19%. Consequently, the use of white lupine in the formulations of complete feed, makes it possible to improve their nutritional value. And the use of lupine without a shell makes it possible to replace high-fingered animal feed in greater volume.

Dietary nanoselenium supplementation for heat-stressed rainbow trout: effects on organizational structure, lipid changes, and biochemical parameters as well as heat-shock-protein- and selenoprotein-related gene expression

Nanoselenium (nano-Se) shows unique protective effects against environmental heat stress in rainbow trout as a selenium source additive and free radical scavenger. Accordingly, we investigated the effects of supplementation with different levels of nano-Se (0, 5, and 10 mg/kg) and before and after heat stress (24°C) for different treatment times on the dynamic changes of rainbow trout liver tissue structure, lipid changes, biochemical properties, and gene expression. The results showed that, under heat stress, the fish supplementation of 5 mg/kg nano-Se significantly increased liver glutathione peroxidase (GPx) activity and upregulated expression levels of HSP70b, HSP90a1, GPx1a, and Trx mRNAs, while liver alanine aminotransferase (ALT), aspartate aminotransferase (AST), superoxide dismutase (SOD), and malondialdehyde (MDA) levels as well as tissue structure damage and lipid accumulation were decreased. Combining the trends for the above indicators indicated that stress began to increase significantly at 8 h. It can be concluded that supplementation with 5 mg/kg nano-Se effectively alleviates stress damage in rainbow trout. Furthermore, stress at 24°C for 8 h can be thought of as a critical time point for the study of heat stress in rainbow trout, with significant changes in response but no serious damage. Thus, these results provide a reference for the addition of nano-Se to rainbow trout feed and provide theoretical and practical guidance for enhancing the resistance of rainbow trout to heat stress.

Effects of Partial Substitution of Conventional Protein Sources with Duckweed (Lemna minor) Meal in the Feeding of Rainbow Trout (Oncorhynchus mykiss) on Growth Performances and the Quality Product.

Duckweed (Lemna minor) meal was included in the formulation of three experimental feeds (L1, L2, L3) for rainbow trout at 10%, 20%, 28% of the protein source, respectively. Increasing the duckweed inclusion, the other protein sources were adjusted to get isonitrogenous (41%) and isolipidic (20%) diets, as the control diet (LC). 540 fish (mean body weight 124.5 ± 0.7 g) were randomly allocated in 12 tanks divided equally among the four different diets. After 90 days, fish were weighed and the most important productive performances, fillet quality and fatty acid profile were determined. The final body weight in L1 (340.53 g) and L2 (339.42 g) was not different from LC (348.80 g); L3 trout significantly (p < 0.05) exhibited the lowest one (302.16 g). Similar trends were found in final mean length, weight gain, specific growth rate, food conversion rate. Somatic indices were affected by duckweed inclusion. Diets had not significant effects on the proximate composition and fatty acids of the fillet in L1, L2, L3 respect to LC. Based on this study, duckweed meal derived from Lemna minor can be included in the feed for the rainbow trout without negative effects on the growth performances at 20% of the protein substitution.

Modulation of humoral immunological and antioxidant responses and gut bacterial community and gene expression in rainbow trout, Oncorhynchus mykiss, by dietary lactic acid supplementation

The present study was conducted to find the effects of dietary lactic acid (LA) supplementation on growth performance, hematological characteristics, humoral antioxidant and immunological factors, intestinal gene expression and bacteriological parameters in rainbow trout, Oncorhynchus mykiss. The fish (104 ± 0.90 g) were randomly distributed in twelve tanks (150 L water) as four treatments, receiving diets supplemented with 0, 5, 10, and 20 g/kg LA for 70 days. At the end of the feeding trial, no significant differences were observed in the fish growth performance and survival among the treatments. Blood/plasma red blood cell (5–20 g/kg LA), white blood cell (10 g/kg LA), hematocrit (5 and 10 g/kg LA), hemoglobin (5 and 10 g/kg LA), superoxide dismutase (10 g/kg LA), glutathione peroxidase (10 g/kg LA), total antioxidant capacity (10 g/kg LA), lysozyme (5–20 g/kg LA), and alternative complement activity (10 g/kg LA) significantly increased, as malondialdehyde (10 g/kg LA) significantly decreased in the LA-treated fish. Dietary LA supplementation induced no significant changes in the intestinal defensin gene expression, but significantly up-regulated the expression of toll-like receptor-3 (5–20 g/kg LA), Mx-9 (5–20 g/kg LA), and heat shock protein-70 (5 g/kg LA) genes; the highest expressions were observed at 5 g/kg LA supplementation. Dietary LA supplementation significantly increased total bacterial count (5 and 10 g/kg LA), Lactobacillus sp. (5–20 g/kg LA), and Bacteroides sp. (5–20 g/kg LA), but decreased Streptococcus iniae (5–20 g/kg LA) in the fish intestine; the highest Lactobacillus sp. And Bacteroides sp. Were observed in 10 and 5 g/kg LA supplementation, respectively. Overall, dietary LA supplementation, although has no significant effects on the fish growth performance, is beneficial to improve humoral antioxidant parameters, humoral and intestinal immunological parameters and intestinal microflora. According to the results, dietary 5–10 g/kg LA is recommended for the formulation of rainbow trout feed.

Asymmetric competition over space use and territory between native brown trout (Salmo trutta) and invasive brook trout (Salvelinus fontinalis).

Interference competition over food and territory can shape population structure and habitat use within and between species. The introduction of invasive species often leads to novel competitive interactions over shared resources and invaders can eventually exclude the native species from preferred habitats. Invasive brook trout (Salvelinus fontinalis) introduced to northern Europe have excluded native brown trout (Salmo trutta) from numerous headwater streams. The fact that invasive brook trout can displace the more aggressive brown trout is puzzling. However, the earlier spawning and hatching of brook trout, compared to brown trout, may lead to unequal competition due to size advantage and prior resident status of brook trout at the fry stage. In this study, we examine the effect of competition between brown trout and brook trout using the natural size distribution of the two species. In two consecutive experiments, we first measured space use and feeding of a fry (age 0+) in the presence of a juvenile (age 1+). In experiment 2, we assessed territorial interactions between the species at the fry stage (age 0+) and if smaller brown trout could compensate the disadvantage by manipulating residence duration. Fry of brook trout feed sooner and spend more time close to the larger individual than brown trout fry. We also found that brook trout fry won most territorial contests against brown trout, and that increased residence duration led to longer and more aggressive interactions. The results suggest that smaller brown trout are displaced to suboptimal habitats in the presence of a larger brook trout. Therefore, the later emergence from gravel beds resulting in the naturally occurring size disadvantage of brown trout at the fry stage may lead to unequal territorial interactions that could explain why brown trout are displaced from preferred habitats in sympatry with brook trout.

Metabonomics analysis reveals the protective effect of nano‑selenium against heat stress of rainbow trout (Oncorhynchus mykiss)

Nano‑selenium (nano-Se) shows high biological activity and low toxicity, and has emerged as an ideal antioxidant. Our goal was to determine the underlying mechanism of nano-Se-mediated heat stress tolerance in rainbow trout (Oncorhynchus mykiss). Using liquid chromatography–mass spectrometry (LC–MS) metabolomics, histomorphology, and conventional biochemical assays, we investigated the physiological responses of heat-stressed rainbow trout to nano-Se. Fish were fed to two levels nano-Se at 18 °C for 9 days: CG18 (0 mg/kg) and Se18 (5 mg/kg). The water temperature of all groups was increased to 24 °C and maintained for 8 h (CG24, Se24). The results showed that most glycerophospholipids and CoA levels were decreased in CG18-CG24, and pathway enrichment analysis showed that it mainly interfered with glycerophospholipids and fatty acid metabolism. Meanwhile, hematoxylin and eosin and Oil Red O staining showed significant damage to CG18-CG24, which was ameliorated by Se18-Se24. The results combining analysis of antioxidant enzymes and heat shock proteins further support the notion that nano-Se supplementation inhibited galactose metabolism and activated the glutamate-glutamine metabolic pathway as the key metabolic strategy against heat stress. These results could establish heat stress defense strategies and increase our understanding of the mechanism of nutrient participation in fish's response to adverse environments. SignificanceGlobal warming is affecting the distribution and survival of cold-water fish worldwide, through seasonal water temperature increases and an increase in the frequency of extreme heat wave events. Surprisingly, Nano‑selenium (Nano-Se) with its outstanding advantages of high biological activity and low toxicity, making it a good Se nutrient supplement and free radical scavenger, and also an ideal and ecological way to supplement Se. How to utilize the metabolome to better address the complexity of the interactions that may occur with Nano-Se during the process of heat stress resistance is an important challenge. In the present study, this is the first publicly available metabonomics study of the anti-heat stress effect of Nano-Se as a nutrient on rainbow trout liver. These data indicated that Nano-Se effectively alleviated stress damage in rainbow trout, in which heat stress interfered with the metabolism of glycerophospholipids and fatty acids significantly, causing liver cell membrane damage and lipid metabolism disorders in rainbow trout. Meanwhile, supplementation of Nano-Se downregulated galactose metabolism and activated glutamate and glutamine metabolic pathways, which seems to be a key metabolic strategy to combat heat stress. The results provide a scientific basis for the development of an anti-heat-stress feed for rainbow trout that help maintain their health, productivity and welfare under unfavorable heat conditions.

Safety and efficacy of a feed additive consisting of astaxanthin-rich Phaffia rhodozyma for salmon and trout (Igene Biotechnology, Inc.).

Following a request from the European Commission, the FEEDAP Panel was asked to deliver a scientific opinion on the safety and efficacy of astaxanthin (ATX)‐rich Phaffia rhodozyma. The additive, belonging to the category ‘sensory additives’ and the functional group ‘substances which, when fed to animals, add colours to food of animal origin’ is intended to be used in feed for salmon and trout from an age of six months onwards up to a maximum content of 100 mg ATX/kg complete feed. The product is produced by the telemorph of Phaffia rhodozyma, Xanthophyllomyces dendrorhous, and it is declared to contain 995 g dried inactivated biomass and 5 g ascorbic acid per kg additive. The main active principle of the additive is ATX; however, the FEEDAP Panel noted that some other carotenoids are also present in lower quantities. The minimum ATX concentration is specified to be 5,000 mg per kg additive. The yeast Xanthophyllomyces dendrorhous is considered by EFSA to be suitable for the qualified presumption of safety (QPS) approach to safety assessment; therefore, the use of the production strain in the production of the additive would not raise any safety concern for the target species, the consumers of products from animals fed the additive and the environment. In the absence of a tolerance study with the additive, the FEEDAP Panel cannot conclude on the safety for the target species. In the absence of residue and toxicity data of ATX, no final conclusions on the safety for the consumer can be drawn. The FEEDAP Panel concluded that the additive is irritant to skin and eyes, and a skin and respiratory sensitiser, although exposure by inhalation is likely low. The FEEDAP Panel considers that ATX from the biomass does not pose a significant additional risk to the environment compared with other natural sources of ATX. In absence of adequate evidence, no conclusion can be made on the efficacy of the additive.

Involvement of Taste Receptors in the Oro-Sensory Perception of Nutrients in Rainbow Trout (Oncorhynchus mykiss) Fed Diets with Different Fatty Acid Profiles

Taste perception plays an important role in an animal’s detection of nutrients, conveying key dietary information, fundamental for its growth and survival. Because alternative terrestrial ingredients are known to affect the feeding of rainbow trout (RT, Oncorhynchus mykiss), we aimed to assess the importance of taste receptors in detection. Using self-feeders, we examined the feeding behavior (30 days of a feeding trial followed by 10 days of a preference trial) of RT fed with a commercial diet (C), vegetable diets supplemented with linseed oil (V1) or algal oil (V2). During the feeding trial those fed V2 decreased their food intake. The preference trial revealed that fish preferred V2 v. C and V1 v. V2 for fish which had consumed V1 and C during their feeding trial. Mechanistically, taste receptors were mainly expressed in taste organs and regulated by diet, which indicated the function of the taste receptors. Some taste receptors for fatty acids (such as the ffar receptor) and amino acids (such as the tasr receptor) were highly expressed in the RT tongue. While ffar2a transcripts were upregulated by vegetal diets in the tongue, ffar1 and ffar4, known for important roles in mammals, were very low expressed and not found in the RT genome, respectively. Overall findings show that RT displayed the fundamental mechanisms for oro-gustatory perception of nutrients related to different diet composition.

Effect of dietary supplementation of Neem, Azadirachta indica leaf extracts on enhancing the growth performance, chemical composition and survival of rainbow trout, Oncorhynchus mykiss

Rainbow trout Oncorhynchus mykiss has a great nutritional value and delicious taste. A 90-days experimental trial was conducted to investigate the effect of dietary leaf extract of neem tree Azadirachta indica as a feeding supplement on the growth performance and proximate composition of O. mykiss. Four experimental diets were designed as T1 (with 5% A. indica leaf extract), T2 (with 7% of A. indica leaf extract), T3 (with 10% A. indica leaf extract), and T4 (control group feed with a regular diet with 0% A. indica leaf extract). The average initial weight of fry 0.4 ± 0.14 g was stocked at 25 fish/tank with two replicates per treatment (4 × 2 = 8). After 90 days of the experimental trial, One-way ANOVA showed significant differences in final body weight, weight gain, specific growth rate, feed conversion ratio, and survival rate among the treatment groups (p < 0.05). The highest final body weight (48.10 g) and weight gain (47.70 g) was observed in T2 with 7% A. indica leaf extract, which was significantly different from the other treatments (p < 0.05). The lowest FCR was recorded in T2 (1.90), which was significantly different compared to other treatment groups (p < 0.05). Inclusion of A. indica leaf extract in formulated feed for rainbow trout had significant effects in the hepatosomatic index, viscerosomatic index and Fulton’s condition factor (p < 0.05), but there was no significant difference in the survival rate of rainbow trout fry treated with different experimental diets (p > 0.05). The phenomenal regression indicates that 7.5% A. indica inclusion is optimum for best growth performance for rainbow trout under a controlled environment. Thus, the present study suggests that the dietary leaf extract has performed an excellent nutritional supplement by enhancing growth performance and health conditions of rainbow trout in the hatchery conditions.

Effects of date (Phoenix dactylifera L.) kernel essential oil on growth performance and innate immunoassay in rainbow trout (Oncorhynchus mykiss) juveniles

This study aimed to investigate the effects of date (Phoenix dactylifera L.) kernel essential oil on growth and development performance parameters as well as phagocytic activity, respiratory burst activity, superoxide dismutase, lysozyme activity, and myeloperoxidase activity from immune parameters of rainbow trout (Oncorhynchus mykiss). The nutritional study was performed for 45 days to assess the effect of three concentrations (0.5, 1, and 2 mL kg-1) of date kernel essential oil in rainbow trout. β-citronellol, an important compound in many respects, was found 31.70% in date kernel oil. It has been determined that the addition of date kernel essential oil to rainbow trout feed decreases the feed conversion rate, increases the percent body weight gain, and the specific growth rate. It was observed that phagocytic activity, respiratory burst activity, and myeloperoxidase activity values improved in date kernel essential oil added groups, however, superoxide dismutase and lysozyme activity values were not affected. Consequently, date kernel essential oil can be act as a growth promoter, increase innate immunity, and cheap feed additive for the rainbow trout juveniles.

Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss).

Alternative sources of fish oil (FO) are one of the major problems in aquaculture; therefore, the goal of the present study was to examine insect (black soldier fly larvae) oil (BSLO) as a potential replacer of fish/soy oil in juvenile rainbow trout (initial average weight of 32 ± 0.15 g) feed. Four diets were formulated wherein FO (control diet) was completely replaced with either soybean oil (SO) or BSLO, and an additional BSLO-based diet supplemented with 1.5% bile acid (BSLO + BA) were fed to the fish for 10 weeks. Growth performance of the BSLO fed group was similar (P > 0.05) to that of the FO and SO fed groups, however, the fish fed BSLO + BA diet registered the lowest growth (P < 0.05). Oil sources did not (P > 0.05) affect the major nutrient content of whole-body, however, the fatty acid composition of the muscle and liver was influenced (P < 0.05), with the highest 14:0, 16:0, and total saturated fatty acid detected in BSLO or BSLO + BA fed trout compared to the others (P < 0.001). No significant differences were observed in eicosapentaenoic acid + docosahexaenoic acid (EPA + DHA) or total n-3 polyunsaturated fatty acid (PUFA) content in muscle among the groups, whereas, the highest EPA:DHA and n-3:n-6 ratios were detected in the FO group. Gene expression for fatty acid binding protein (fabp), fatty acid synthase (fas), and Δ5 desaturase in the liver was lower in FO (P < 0.05), while BSLO + BA registered the highest Δ6 expression (P = 0.006). Supplementation of BA in the BSLO diet increased superoxide dismutase (SOD) and catalase (CAT) activities compared to the other groups (P < 0.05). In conclusion, BSLO could serve as a substitute for FO and SO in rainbow trout diet without negatively impacting growth performance, whole-body composition and nutrient retention, and modulate the expression of fatty acid metabolism-related genes in rainbow trout.

Application of probiotics in trout farms in North-West Russia

In recent years, various probiotic and immunomodulating drugs have been actively used in aquaculture. The group of probiotics includes preparations of the Vetom series, created on the basis of the spore-forming bacteria Bacillus subtilus and Bacillus licheniformis. Recently, a large positive experience has been accumulated in the use of Vetom 1.1 in fish farming. The drug is actively used in trout cage farms in Karelia and the Leningrad region. Vetom 1.1 was administered orally with food at a dosage of 50–75 mg/kg ichthyomass per day for 10 days. An improvement in the epizootic state of fish was observed: regeneration of the affected fins and branchial epithelium, normalization of the blood state. Biocomplex Multibacterin (previously in research — Multibacterin OMEGA-10) is a functional food based on lactobacillus (Lactobacillus acidophilus). The drug has a high antagonistic activity against microorganisms — pathogens of bacterial etiology, stimulates the synthesis of immunoglobulins, improves metabolic processes in the body of animals, and stimulates regeneration processes. Multibacterin is recommended for introduction into trout feed in case of toxicosis, bacterial and fungal infection at a dosage of 0.1 ml/kg of ichthyomass for 10 days. The study of the effect of the Multibacterin biocomplex on the state of rainbow trout of different age groups, reared under different conditions, was carried out. With the introduction of the probiotic Multibacterin into the feed, a decrease in the death of fish was noted to 9.5% versus 20% in the control. An improvement in the state of the branchial epithelium was revealed, and the development of the regenerative process on the affected branchial lobes was noted. These preparations help to maintain the immunity of fish and can be recommended for use in aquaculture.

Optimizing the fatty acid profile of novel terrestrial oil blends in low fishmeal diets of rainbow trout (Oncorhynchus mykiss) yields comparable fish growth, total fillet n-3 LC-PUFA content, and health performance relative to fish oil

Identifying and effectively utilizing suitable, novel, terrestrial oil sources either alone or as blends to replace fish oil (FO) is a prerequisite for improving the sustainability of global aquaculture. Therefore, the present study evaluates several novel terrestrial oil blends (TOBs), optimized for their fatty acid profile, as alternatives to FO in low fishmeal diets fed to rainbow trout (Oncorhynchus mykiss) and describes the subsequent effects on fish growth, fatty acid composition and health. Insect oil (IO), genetically modified canola oil (CO), palm oil (PO) and linseed oil (LO) were used for the formulation of three TOBs viz., TOB-1 (30%IO+36%CO + 34%LO), TOB-2 (40%PO + 20%CO + 40%LO) and TOB-3 (50%TOB-1 + 50%TOB-2). Formulas TOB-1 and TOB-2 considered the total fatty acid profile based upon the general FO fatty acid profile, published fatty acid research for rainbow trout, and the fatty acid requirements of rainbow trout. A low fishmeal based basal diet containing 44% crude protein was formulated, and FO, TOB-1, TOB-2 and TOB-3 were incorporated in the basal diet to prepare the experimental diet groups, Control, TOB-1, TOB-2 and TOB-3, respectively. All experimental diets were fed to triplicate groups of rainbow trout juveniles (initial weight 7.9 ± 0.02 g) for 9 weeks. Growth performance (final weight, percent weight gain and specific growth rate) in TOBs fed groups were equal to the FO-based control group. Fish fed the TOB-3 diet consumed more feed followed by the control and TOB-1 diet groups. Significantly lower feed intake was observed in the TOB-2 diet group. Feed conversion ratio and protein efficiency ratio were not significantly influenced by dietary oil sources. Fish fed the control diet showed significantly higher hepatic lipid content compared to TOB groups, followed by TOB-2, TOB-3, and TOB-1, which was significantly lower in hepatic lipid content. Muscle lipid content and whole-body major nutrient compositions were not significantly influenced by the dietary oil sources. Fatty acid composition of muscle and liver reflected that of the diets. Maximum values for n3 LC-PUFAs (EPA and DHA), lauric acid (C12:0) and C18:3n-3 were observed in the FO, TOB-1 and TOB-2 groups, respectively. Except for C12:0, muscle saturated fatty acid contents were significantly lower in TOBs-based diet compared to the FO-based control diet fish. As expected, muscle C12:0 content was significantly higher in the TOB-1 group followed by the TOB-3 group. TOB-2 and control groups had significantly lower content of C12:0. The fillet total n-3 LC-PUFA was significantly higher in fish fed the control diet group followed by TOB-3 and TOB-2 groups, TOB-1 showed significantly lower content of total n-3 LC- PUFA. Hepatic delta-5 desaturase (Δ5fad), delta-6 desaturase (Δ 6fad) and fatty acid elongase-2 (Elovl-2) gene expressions were significantly influenced by dietary oil sources, where TOB-based groups showed higher Δ6fad and Elovl-2 expressions. Measured innate immunity and antioxidant markers were not affected by TOBs. Finally, we concluded that TOBs could serve as a substitute for FO in rainbow trout feed without negatively impacting performance. Moreover, fillet total n-3 LC-PUFA of TOB-fed fish satisfies the suggested daily serving for humans.