Diets For Rainbow Trout Research Articles

The effect of gradual addition of camelina seeds in the diet of rainbow trout ( Oncorhynchus mykiss ) on growth, feed efficiency and meat quality

Camelina (Camelina sativa) is a robust crop to cultivate and a potential source of protein, oil and n-3 fatty acids for aquaculture. The aim of this study was to examine the effects of camelina seed in feed on rainbow trout (Oncorhynchus mykiss) performance and nutritional composition of the muscle. A mixture of faba bean, wheat gluten meal and rapeseed oil was gradually replaced by camelina seed (0%, 10% and 20% camelina in the diet). Fifty 0+ old fish were placed in each of the 12 recirculation aquaculture tanks to enable three treatments with four replicates. Camelina seed inclusion did not affect the growth performance, crude protein or fat content of fish body. The moisture content was the lowest (p = 0.021) with 20% camelina. The vitamin D3 contents in fish muscle were low, indicating that camelina may slightly impair the absorption of vitamin D3 (p = 0.055). Camelina diets decreased (p < 0.001) the proportion of monounsaturated fatty acids and increased (p < 0.001) polyunsaturated fatty acids and n-3 fatty acids, particularly α-linolenic acid, in fish muscle. Camelina seed proved to be a potential plant-based ingredient for rainbow trout feed.

Transgenic camelina oil is an effective source of eicosapentaenoic acid and docosahexaenoic acid in diets for farmed rainbow trout, in terms of growth, tissue fatty acid content, and fillet sensory properties

AbstractThe oilseed Camelina sativa was genetically engineered to produce eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) at levels similar to fish oil (FO), which we tested as a lipid source in diets for rainbow trout. Three experimental diets were tested, a FO control, a low‐level transgenic camelina oil (LCO) diet (no FO with 12.5 g/kg camelina), and a high‐level transgenic camelina oil (HCO) diet (no FO with 130 g/kg transgenic camelina). Trout (initial weight 49.8 ± 11 g/fish) were fed for 12 weeks and were evaluated for growth performance, fatty acid content (muscle, liver, brain, and eye), and sensory properties of fillets. The final lengths and weights of fish fed LCO and HCO diets were higher compared to fish fed FO. There were no differences in weight gain, condition factor, specific growth rate, feed intake, and feed conversion ratio. EPA in muscle tissue was higher in fish fed HCO and FO diets compared to the LCO diet. Compound‐specific stable isotope analysis revealed that rainbow trout fed the FO diet stored isotopically enriched DHA compared to the lighter DHA in fish fed HCO. Trout fillets from the HCO treatment were firmer in texture and had a higher orange intensity compared to the FO group.

Partially replacing fish oil with microalgae ( Schizochytrium limacinum and Nannochloropsis oceanica ) in diets for rainbow trout ( Oncorhynchus mykiss ) reared in saltwater with reference to growth performance, muscle fatty acid composition and liver ultrastructure

Partially replacing fish oil with microalgae ( <i>Schizochytrium limacinum</i> and <i>Nannochloropsis oceanica</i> ) in diets for rainbow trout ( <i>Oncorhynchus mykiss</i> ) reared in saltwater with reference to growth performance, muscle fatty acid composition and liver ultrastructure

Fat encapsulation and supplementation with free amino acids cannot compensate for negative effects from dietary rapeseed protein isolate on growth performance of rainbow trout (Oncorhynchus mykiss)

There are still restrictions when using rapeseed protein products as fish meal alternatives in diets for rainbow trout. Digestibility of a particularly purified rapeseed protein isolate (protein content: 98.7 g 100g−1) was determined in rainbow trout (initial body weight: 178.2 ± 20.9 g) and it was used to exchange fish meal gradually (0 %, 66 % and 100 %) in diets based on commercial trout diets. To overcome potential limiting factors on growth performance from rapeseed protein isolates, duplicates of these experimental diets were encapsulated with stearic acid and one diet devoid of fish meal included rapeseed protein isolate as well as a mixture of free amino acids. The highest recorded crude protein digestibility (mean = 99.8 % ± standard deviation = 1.6 %) of rapeseed protein was reached using the stripping method. Daily feed intake (DFI) of the dietary group devoid of fish meal (DFI: 2.1 ± 0.06) was significantly reduced in comparison with control (DFI: 2.6 ± 0.07) at the end of the experiment. Similarly, feed conversion ratio (FCR) was significantly impaired when comparing control (FCR: 0.9 ± 0.01) to the dietary group with complete exchange of fish meal (FCR: 1.1 ± 0.02). Neither encapsulation of diets nor supplementation with free amino acids could overcome negative effects on growth performance from dietary rapeseed protein isolate inclusion. Results suggest that even highly purified rapeseed protein products can impair growth performance of rainbow trout and that factors other than ANFs could determine the effectiveness of rapeseed protein products as fish meal alternatives.

Schizochytrium sp. (T18) Oil as a Fish Oil Replacement in Diets for Juvenile Rainbow Trout (Oncorhynchus mykiss): Effects on Growth Performance, Tissue Fatty Acid Content, and Lipid-Related Transcript Expression.

Simple SummaryOne of the main concerns in aquaculture is the overreliance on wild-sourced fish oil as the main source of omega-3 fatty acids in diets for farmed fish. Microbes, such as Schizochytrium, naturally produce high levels of omega-3 fatty acids that could potentially replace fish oil in aquaculture feeds. In this study, we tested the oil from a new strain of Schizochytrium (T18) to replace fish oil in diets for farmed rainbow trout and looked at fish growth performance, muscle and liver fatty acid content, and the expression of transcripts involved in fat metabolism. Trout were raised for 8 weeks and fed diets with either: (1) fish oil control, (2) low inclusion of microbial oil, or (3) higher inclusion of microbial oil. Inclusion of Schizochytrium sp. (T18) oil at high or low levels in the diet resulted in a similar growth performance as seen in trout fed the control diet; however, muscle and liver fatty acid profiles were impacted by diet. Overall, our results showed that Schizochytrium (T18) is an effective source of omega-3 fatty acids in diets for rainbow trout.In this study, we evaluated whether oil extracted from the marine microbe, Schizochytrium sp. (strain T18), with high levels of docosahexaenoic acid (DHA), could replace fish oil (FO) in diets for rainbow trout (Oncorhynchus mykiss). Three experimental diets were tested: (1) a control diet with fish oil (FO diet), (2) a microbial oil (MO) diet with a blend of camelina oil (CO) referred to as MO/CO diet, and (3) a MO diet (at a higher inclusion level). Rainbow trout (18.8 ± 2.9 g fish−1 initial weight ± SD) were fed for 8 weeks and evaluated for growth performance, fatty acid content and transcript expression of lipid-related genes in liver and muscle. There were no differences in growth performance measurements among treatments. In liver and muscle, eicosapentaenoic acid (EPA) was highest in trout fed the FO diet compared to the MO/CO and MO diets. Liver DHA was highest in trout fed the MO/CO diet compared to the FO and MO diets. Muscle DHA was highest in trout fed the MO and MO/CO diets compared to the FO diet. In trout fed the MO/CO diet, compared to the MO diet, fadsd6b was higher in both liver and muscle. In trout fed the FO or MO/CO diets, compared to the MO diet, cox1a was higher in both liver and muscle, cpt1b1a was higher in liver and cpt1a1a, cpt1a1b and cpt1a2a were higher in muscle. Schizochytrium sp. (T18) oil was an effective source of DHA for rainbow trout.

Dietary inclusion of a partially defatted black soldier fly (Hermetia illucens) larva meal in low fishmeal-based diets for rainbow trout (Oncorhynchus mykiss)

BackgroundRecent investigations highlighted that Hermetia illucens (BSF) larva meal can be a valuable alternative protein source for aquafeed production. In this study, in substitution of fishmeal, we used increasing inclusion levels of a partially defatted BSF larva meal in low fishmeal-based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and we evaluated the related implications in terms of growth performance, physical characteristics, proximate and fatty acid (FA) compositions of the fillets, gut and liver histology, and diet digestibility. In a 131-day trial, 576 fish (100.1 ± 9.29 g) were randomly allotted to 24 tanks (24 fish/tank, 4 replicates/treatment). Six experimental diets were produced to have partial replacement of fishmeal (0, 10%, 20%, 30%, 40% and 50%) by increasing levels of BSF meal (0% [BSF0], 3% [BSF3], 6% [BSF6], 9% [BSF9], 12% [BSF12] and 15% [BSF15] on as fed basis, respectively).ResultsNo differences were observed among the treatments for all the considered growth performance parameters. The viscero and hepato-somatic indexes showed significant differences among the treatments, with the highest values observed in the BSF15 group. No differences were recorded in terms of fillet’s physical characteristics, dry matter (DM), crude protein (CP) and ether extract (EE) contents. Total saturated and monounsaturated FA increased, while polyunsaturated FA (particularly n-3 FA) decreased while increasing the HI meal inclusion in the diet. Histopathology of liver and gut was not affected, whereas, in posterior gut, villi were higher in BSF6 and BSF9 compared to BSF3 fish. The apparent digestibility of DM, CP, EE and gross energy did not vary among the treatments.ConclusionsThese results suggest that a partially defatted BSF meal could be included up to 15% in low fishmeal-based diets for rainbow trout with no adverse effects on growth performance, fillet’s physical characteristics, gut and liver health, and diet digestibility. On the contrary, the fillet FA composition worsened while increasing the level of BSF meal in the diet.

Gökkuşağı Alabalığı (Oncorhynchus mykiss Walbaum, 1792) Yemlerinde Soya Küspesi Yerine Yer Fıstığı Küspesi (Arachis hypogaea L.) Kullanımının Büyüme, Biyokimyasal Kompozisyon ve Fileto Rengi Üzerine Etkileri

The aim of this study was to determine the effect of using peanut meal (Arachis hypogaea L.) instead of soybean meal in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) feeds on growth performance, biochemical composition and fillet color. For this purpose, rainbow trout were fed for eight weeks with four different diets adjusted as iso-nitrogenic (45% protein), iso-lipidic (19% lipid) and iso-energetic (22 kJ g-1). While the CF (commercial feed) group was fed with commercial feed, three experimental diets containing 0% (Control-C), 50% (PNM50) and 100% (PNM100) peanut meal were formulated for the other groups. As a result of the 8 weeks diet treatments, the best final weight, weight gain and specific growth rate were found PNM50 group and the difference among groups was significant. The use of peanut meal instead of soybean meal in rainbow trout diets decreased fish meat protein ratios compared to CF and C groups. The qualities of redness, yellowness and hue were distinct between the diets in the dorsal and caudal locations. At all the measured regions in the C and CF groups did not result in any significant difference for chroma. It is thought that the differences between the measured regions in L*, a*, b * are due to the fillet thickness and the preservation of the fillet coloring matter. Consequently, 50% peanut meal instead of soybean meal in trout diets could be used in diets of rainbow trout without any negative effects on growth.

ИСПОЛЬЗОВАНИЕ БИОМАССЫ НАСЕКОМЫХ ДЛЯ ВЫРАЩИВАНИЯ РАДУЖНОЙ ФОРЕЛИ В АКВАКУЛЬТУРЕ (КРАТКИЙ ОБЗОР ЗАРУБЕЖНОЙ ЛИТЕРАТУРЫ)

The article focuses on the data from foreign literature on growing rainbow trout or mykiss (Oncorhynchus mykiss) with the inclusion of dried and / or fat-free insect biomass in diets. The following seven types of insects could be recommended for inclusion in the diet of rainbow trout and other fish species: larvae and / or pupae of diptera fly (Hermetia illucens), housefly (Musca domestica), flour worm larva (Tenebrio molitor), locusts and grasshoppers (Acrididae), crickets (Gryllidae) and cathidids (Tettigoniidae), silkworm pupae (Bombyx mori). The brief data on physiology and life cycle of these insects are given, as well as the data on proteins and fatty acids concentration in fresh and dry larvae of insects. It has been shown that the flour from dried insect biomass contains a large amount of amino acids and fatty acids. There has been given the data on the influence of flour from insect larvae on the mass increase of rainbow trout juveniles and adults, digestibility of feed dry matter, organoleptic characteristics of fish fillets, amino acid and fatty acid composition, and other indicators. It has been found out that in most cases the survival rate is significantly higher in the experimental groups of Oncorhynchus mykiss juveniles fed a diet containing insect flour. It has been inferred that including flour from insect biomass in certain proportions has a positive effect on the growth and life of Oncorhynchus mykiss species. The most promising is adding Hermetia illucens larvae flour in the diet of rainbow trout in aquaculture, because Hermetia illucens larvae have the highest biomass yield per unit time compared to other insects.

Effects of Dietary Natural Zeolite (Clinoptilolite) on Growth and Some Blood Parameters of Rainbow Trout (Onchorynchus mykiss, Walbaum 1792)

This study was performed to evaluate the effects of adding different levels of natural zeolite (clinoptilolite) to juvenile rainbow trout (Onchorynchus mykiss) diets about growth performance and some biochemical blood parameters. The experimental system was designed as a semi-recirculating aquaculture system and 20 rainbow trouts which weigh 7.91±0.03 g distributed randomly for each tank (300 L). Fish were fed to apparent satiation with diets containing 45% crude protein and 14% crude fat for 70 days which included no zeolite (Control), 0.5% zeolite (Z05), 1% zeolite (Z1), 2.5% zeolite (Z25) in triplicate. Finally, blood samples were collected from all fish tanks to analyze some biochemical blood parameters like cholesterol, triglycerides, LDL, HDL, and VLDL. At the end of the experiment, Z25 group showed negative results in final body weight, weight gain, and specific growth rate (p&amp;lt;0.05). Although Z05 group showed no significant difference, it showed the best results in final body weight, weight gain, specific growth rate, feed intake, feed conversion rate, and protein efficiency. In terms of blood parameters, all the groups had similar values with no significance (p&amp;gt;0.05) compared to the control group. As a result, there was a tendency towards decreased growth and feed utilization due to the addition of zeolite higher than 1% in diets. It could be concluded that limited usage of clinoptilolite in rainbow trout diets might have beneficial effects on growth parameters.

Effect of Dietary Sumac (Rhus coriaria L.) Supplementation on Non-Specific Immune Response and Hematology of Rainbow Trout (Oncorhynchus mykiss), Resistance Against Vibrio anguillarum

This study aimed to investigate the effects of sumac (Rhus coriaria L.) fruit powder in different concentrations as feed additives on non-specific immune response, hematology, and the disease resistance in rainbow trout (Oncorhynchus mykiss). Fish (35.67±0.88 g) were fed with experimental diets (1.0, 3.0, 5.0 and 10.0 g kg-1) at four different concentration. There were no significant differences between groups fed with sumac fruit powder and control group by the mean of red blood cell count (RBC), white blood cell count (WBC), differential leukocytes count (monocyte, lymphocyte, and neutrophile), hematocrit (Hct), hemoglobin (Hb), cell hemoglobin (MCH pg), cell hemoglobin concentration (MCHC %), cell hemoglobin volume (MCV µm3) and plasma lysozyme, Immunoglobulin M (IgM), total protein level on the 8 weeks. After 8 weeks of feeding, fish were challenged with Vibrio anguillarum and cumulative mortality was recorded over 21 days. Dietary administration of 1.0, 3.0, and 5.0 g kg−1 sumac fruit powder significantly increased fish survival rate (p&amp;lt;0.05). The 10.0 g kg−1 diet received fish showed no mortality post challenged with V. anguillarum. These results showed that the sumac fruit powder improved disease resistance when added to the rainbow trout diet

Feasibility of superworm, Zophobas morio , meal as a partial fishmeal replacer in fingerling rainbow trout, Oncorhynchus mykiss , diet: growth performance, amino acid profile, proteolytic enzymes activity and pigmentation

To characterize the effects of a defatted superworm meal (SWM) on the zootechnical performance and nutrient utilization of fingerling rainbow trout, we provided five practical diets with 0 (control), 10, 20, 30 and 40% SWM to substitute fishmeal. Fingerlings (N = 225; 9.9 ± 0.5 g) were randomly allocated over five treatments in triplicate. After eight weeks, the replacement of fishmeal with SWM up to 110 g/kg did not induce significant variations in the final weight and weight gain rate compared to the control group, while dietary 220 g/kg SWM had negative impacts on the growth and feed utilization attributes. The contents of protein and methionine were significantly reduced in the whole body with incremental dietary SWM. The pepsin and chymotrypsin activities were not influenced in the groups, but the lowest trypsin activity was seen in 40% replacement by SWM (p < .05). Total carotenoid content and redness of the fillet were improved with dietary SWM. No variation was seen in the digestibility of protein and dry matter in diets including 55 g/kg and 110 g/kg SWM compared to the control group (p > .05). Overall, optimum fishmeal replacement by SWM ranged from 162.6 to 184.2 g/kg in rainbow trout diet based on the broken-line regression model.

Digestible energy versus net energy approaches in feed evaluation for rainbow trout (Oncorhynchus mykiss)

Accurate feed evaluation is important for feed formulation in aquaculture. In this study a net energy (NE) evaluation method was tested which recognises differences in the utilisation of the different macro-nutrients (protein, fat and carbohydrates) for growth. Therefore, a feeding trial was performed with feeds that differed in energy level and with a wide contrast in macronutrient composition, reflecting those found in practical rainbow trout diets. The trial was set up in a 2 by 4 factorial design which included two protein levels (CP400 and CP500) and four different fat levels (CF140, CF190, CF240, CF290) coinciding in a wide range in carbohydrate levels. These differences were achieved by starting from a basal high protein and fat diet where protein and or fat were replaced by carbohydrates. These 8 diets were then used to assess the prediction precision of growth performance by a NE approach as compared to a digestible energy (DE) approach in feed evaluation for rainbow trout. The results of the current study showed that replacing fat by carbohydrates reduced the utilisation of energy for growth. This effect was stronger at the highest carbohydrates levels which indicated a curvilinear response in the utilisation of carbohydrates. However in terms of the prediction precision of growth rate an improvement was only shown when using a NE approach using linear efficiencies of digestible macronutrients (R2 = 0.890 compared to R2 = 0.848 for the DE approach). A NE approach assuming a curvilinear effect of carbohydrates did not lead to an improved prediction of growth rate in the current study (R2 = 0.617).

Effects of dietary fish oil replacement by poppy seed oil on growth performance and fillet quality of rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were fed replacement of fish oil with diets including poppy seed oil (PSO; 0%, 50% and 100%). At the end of the 90-day feeding period, the water holding capacity of the fillets decreased when the storage time increased. The colour and pH values were affected by both storage and diets. The hardness, springiness, gumminess and chewiness index of the fillet samples decreased as a consequence of increasing storage time, whereas the cohesiveness values of the fillets increased. The addition of PSO increased unsaturated fatty acids and reduced saturated fatty acids in the fatty acid composition of the fillets. These results demonstrated that the fatty acid (FA) composition of the rainbow trout fillets was reflecting the FA composition of dietary treatments and oils sources. The total mesophilic and psychrophilic bacteria count of the fish oil (FO), poppy seed oil/fish oil (PSO/FO) and poppy seed oil (PSO) samples was found within the legal limit on the third day of storage; however, it was found above the legal limits on the fifth day of storage. The sensory evaluation results showed that the fish fed with PSO diet were found to be non-desirable. The results of the study suggested that the blend of 50% fish oil and 50% poppy seed oil could be used as a replacer of fish oil in diets for rainbow trout to obtained the best growth performance, fillet quality and storage conditions.

Effects of full replacement of dietary fishmeal with insect meal from Tenebrio molitor on rainbow trout gut and skin microbiota

BackgroundAquaculture must continue to reduce dependence on fishmeal (FM) and fishoil in feeds to ensure sustainable sector growth. Therefore, the use of novel aquaculture feed ingredients is growing. In this regard, insects can represent a new world of sustainable and protein-rich ingredients for farmed fish feeds. Accordingly, we investigated the effects of full replacement of FM with Tenebrio molitor (TM) larvae meal in the diet of rainbow trout (Oncorhynchus mykiss) on fish gut and skin microbiota.MethodsA feeding trial was conducted with 126 trout of about 80 g mean initial weight that were fed for 22 weeks with two isonitrogenous, isolipidic, and isoenergetic extruded experimental diets. Partially defatted TM meal was included in one of the diets to replace 100% (TM 100) of FM, whereas the other diet (TM 0) was without TM. To analyse the microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and Qiime pipeline were used to identify bacteria in the gut and skin mucosa, and in the diets.ResultsThe data showed no major effects of full FM substitution with TM meal on bacterial species richness and diversity in both, gut mucosa- and skin mucus-associated microbiome. Skin microbiome was dominated by phylum Proteobacteria and especially by Gammaproteobacteria class that constituted approximately half of the bacterial taxa found. The two dietary fish groups did not display distinctive features, except for a decrease in the relative abundance of Deefgea genus (family Neisseriaceae) in trout fed with insect meal. The metagenomic analysis of the gut mucosa indicated that Tenericutes was the most abundant phylum, regardless of the diet. Specifically, within this phylum, the Mollicutes, mainly represented by Mycoplasmataceae family, were the dominant class. However, we observed only a weak dietary modulation of intestinal bacterial communities. The only changes due to full FM replacement with TM meal were a decreased number of Proteobacteria and a reduced number of taxa assigned to Ruminococcaceae and Neisseriaceae families.ConclusionsThe data demonstrated that TM larvae meal is a valid alternative animal protein to replace FM in the aquafeeds. Only slight gut and skin microbiota changes occurred in rainbow trout after total FM replacement with insect meal. The mapping of the trout skin microbiota represents a novel contribution of the present study. Indeed, in contrast to the increasing knowledge on gut microbiota, the skin microbiota of major farmed fish species remains largely unmapped but it deserves thorough consideration.

Effects of Tenebrio molitor larvae meal inclusion in rainbow trout feed: myogenesis-related gene expression and histomorphological features

The effects of Tenebrio molitor larvae meal (TM) dietary inclusion in rainbow trout diet were evaluated on muscular growth using gene expression and histomorphological features of liver, spleen, kidney, anterior and posterior gut through histopathological analyses. Two hundred fifty-two grow-out rainbow trout were fed four experimental diets containing increasing levels of TM: 0% (TM0), 5% (TM25), 10% (TM50), and 20% (TM100) corresponding to different levels of fish meal replacement (0, 25, 50, and 100%, respectively). Muscular growth was evaluated analysing the expression of various genes involved in different steps of myogenesis. Among the analysed genes, only MyoD expression resulted significantly higher in fish fed TM100 compared to fish fed TM0. The gut histomorphology was not affected by TM dietary inclusion and villus height differs from anterior and posterior segments regardless of the fed diet. Histopathological alterations were observed in all the sampled organs for all the dietary treatments; however, dietary TM inclusion did not influence either development or severity of the observed histopathological changes. The results obtained confirmed the safe utilisation of TM as an alternative protein source in rainbow trout diets and highlighted the necessity to deepen the studies of TM effect on the myogenesis process, especially at a molecular level. Highlights Rainbow trout can effectively be fed with a TM protein source. Total FM substitution by TM (TM100) decreased MyoD gene expression. Increasing TM dietary inclusion did not influence gut histomorphology.

Dietary effect of Lemon Verbena (Aloysia triphylla) extract on growth performance, some haematological, biochemical, and non-specific immunity and stocking density challenge of rainbow trout juveniles (Oncorhynchus mykiss)

ABSTRACT An eight-week feeding trial was conducted to evaluate the effect of lemon verbena (Aloysia triphylla) extract on growth performance, some haematological, biochemical, and non-specific immunity parameters as well as stocking density challenge of rainbow trout (Oncorhynchus mykiss). After adaptation, the fish, with an average weight of 25.52 ± 1.31 g, were fed four different dietary lemon verbena inclusion levels (0, 2.5, 5, and 7 g/kg) for six weeks. In the next step, the number of fish in each tank tripled to expose the fish to density challenges for two weeks. There were differences in the final weight, (SGR), (FCR), (PER), and feed intake between the experimental and control groups (p < 0.05). The results showed that the cortisol content decreased (p < 0.05). The highest levels of FCR, feed intake, plasma triglyceride, cholesterol, (LDL), and (HDL) were observed in the control group. Furthermore, under high stocking density, treatments showed a significant decrease in glucose and cortisol (p < 0.05). A significant increase was also shown in (IgM), (RBA), and (SOD) in all treatments. Finally, using lemon verbena extract, up to 7 g/kg of food can be recommended for rainbow trout diets because it can improve growth performance and non-specific immunity parameters.

The effects of dietary poly‐β‐hydroxybutyrate on growth parameters, intestinal microflora, and histopathology of rainbow trout, Oncorhynchus mykiss, fingerlings

AbstractThe present study aimed to evaluate the effects of poly‐β‐hydroxybutyrate (PHB)‐supplemented diets for rainbow trout (Oncorhynchus mykiss) fingerlings. For this purpose, three experimental diets were prepared to contain 0, 2, and 5% PHB; and each diet was tested in a completely randomized design for 60 days in quadruple groups of 22 fish per tank. The results showed that the inclusion of PHB in the diets did not affect the growth parameters such as mean weight gain, specific growth rate, and feed conversion ratio among treatments. There was also no effect of the PHB on chemical composition, PCR‐DGGE profile of the intestinal bacterial communities, total bacterial count, lactic acid bacteria, psychrophilic bacteria as well as the intestine and the liver histopathology of fish. However, the supplementation of 2 and 5% PHB in the diet significantly reduced total coliform counts, while 5% PHB diet additionally decreased Enterobacteriaceae counts. Both inclusion ratios resulted in significantly higher intestinal villus length and width at the end of the experiment. Considering the positive effects of dietary PHB on intestinal bacterial flora and villus sizes of rainbow trout fingerlings, it can be used as an alternative microbial control agent.Significance StatementPHB is a biopolymer that has previously been reported to have positive effects on fish health, and no literature has been encountered investigating the effects of PHB on rainbow trout fry. The findings obtained in this study show that PHB has positive effects on the intestinal tissues of rainbow trout fry and provides an increase in the number of beneficial bacteria in the gut flora.

Replacing fish oil and astaxanthin by microalgal sources produced different metabolic responses in juvenile rainbow trout fed 2 types of practical diets.

Dietary fish oil supplementation provides n-3 long-chained polyunsaturated fatty acids for supporting fish growth and metabolism and enriching fillet with eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; c22:6n-3). Two experiments were performed as a 3 × 2 factorial arrangement of dietary treatments for 16 wk to determine effects and mechanisms of replacing 0%, 50%, and 100% fish oil with DHA-rich microalgae in combination with synthetic vs. microalgal source of astaxanthin in plant protein meal (PM)- or fishmeal (FM)- based diets for juvenile rainbow trout (Oncorhynchus mykiss). Fish (22 ± 0.26 g) were stocked at 17/tank and 3 tanks/diet. The 100% fish oil replacement impaired (P < 0.0001) growth performance, dietary protein and energy utilization, body indices, and tissue accumulation of DHA and EPA in both diet series. The impairments were associated (P < 0.05) with upregulation of hepatic gene expression related to growth (ghr1and igf1) and biosynthesis of DHA and EPA (fads6 and evol5) that was more dramatic in the FM than PM diet-fed fish, and more pronounced on tissue EPA than DHA concentrations. The source of astaxanthin exerted interaction effects with the fish oil replacement on several measures including muscle total cholesterol concentrations. In conclusion, replacing fish oil by the DHA-rich microalgae produced more negative metabolic responses than the substitution of synthetic astaxanthin by the microalgal source in juvenile rainbow trout fed 2 types of practical diets.

Insect (black soldier fly, Hermetia illucens) meal supplementation prevents the soybean meal-induced intestinal enteritis in rainbow trout and health benefits of using insect oil

Black solider fly larvae (BSFL) and their oils (BSFLO) are receiving increasing attention as sustainable ingredients in fish feeds, but mostly as replacements to marine sources. There were two aims to this study; in exp. 1, soybean meal (SBM)-based diets were formulated to contain BSFL as supplements at 0 (SBM), 8 (SBM + BSFLlow) or 16% (SBM + BSFLhigh) with a control diet being fishmeal-based (FM). In exp. 2, diets included only fish oil (FO), soybean oil (SBO), BSFLO or BSFLO + bile acid (BA), and all lipid sources were added at 16%. Both experiments were run at the same time and fed to rainbow trout (32 g) with each treatment being triplicated. After 10 weeks the fish were sampled for liver and distal intestine histology, expression of genes responsible for inflammation in the intestine and kidneys, and serum peroxidase and lysozyme activities. In exp. 1, supplementations of BSFL effectively prevented SBM-induced intestinal enteritis, down-regulated intestinal prostaglandin and interferon regulatory factor 1 (IRF-1), while the SBM + BSFLhigh diet significantly increased serum lysozyme activity. In exp. 2, BSFLO caused no histomorphological change to the liver or intestine, but kidney interluekin-8, tumor necrosis factor and IRF-1 were significantly upregulated along with significantly higher serum peroxidase activity. The inclusion of BA in the BSFLO diets significantly upregulated intestinal prostaglandin gene expression. Overall, BSFL supplementations of 8 or 16% prevented SBM-induced intestinal enteritis based on histological observations, which was supported by a down-regulation in pro-inflammatory genes and enhanced innate immunity. Meanwhile, the use of BSFLO showed some immunological benefits. Therefore, these sustainable resources are recommended in the diets of rainbow trout, especially when using elevated levels of plant-based proteins.

Effects of a natural hepatomodulator (Bedgen 40TMAS) on the growth performance, body indices, hematological and histological parameters of rainbow trout (Oncorhynchus mykiss) juveniles

ABSTRACT The present study aimed to evaluate the possible effects of a natural hepatomodulator on growth; some biological, blood, and color parameters; body; cost analysis; and liver histology of rainbow trout. A commercial rainbow trout diet was used for the control group, and 500 mg kg−1 of commercial additive was used for the treatment group. The experiment was carried out for 12 weeks. At the end of the experiment, there was no significant effect on growth or biological and some blood parameters (P > 0.05); however, significant skin brightness changes (P < .05) were observed on the fish. Also, liver sections of the fish fed with the control diet showed a high proportion of lipid accumulation on hepatic parenchyma compared to fish that were fed treated diets. These results showed that application of commercial artichoke extract to rainbow trout diets might have positive effects on outer skin colorization and liver fat accumulation.