Indirect estimation of stomach volume of rainbow trout Oncorhynchus mykiss (Walbaum)

The main hypothesis of this study was that if stomach volume is correlated with food intake it can be estimated without laborious and destructive direct measurement. Rainbow trout, Oncorhynchus mykiss (Walbaum), ca. 500–1300 g, were starved for 1, 4, 8 or 16 days at 15°C after which they were fed in excess with dry pellets containing known amounts of X‐ray‐dense markers. Immediately after feeding the fish were killed, X rayed and weighed. Then the stomach was dissected, its contents removed and weighed, and stomach volume was measured. X‐ray plates were developed and feed intake was estimated based on the amount of marker. All measured variables correlated positively with stomach volume. The best fit for linear regression models was obtained for fish starved for 4 days, where stomach content (dry mass) explained 94%, food intake (based on X‐ray measurement) 77% and fish mass 62% of the variation in stomach volume. However, as stomach content measurement can be a lethal, or at least very stressful, event for the fish, the accuracy of food intake measurement (X‐ray) could be increased using multiple regression. In multiple linear regressions, R²‐values varied between 0.79 (16‐day starvation) and 0.91 (1‐day starvation) with food intake and fish mass as explanatory variables for stomach volume. These results indicate that the stomach volume in rainbow trout can be estimated satisfactorily using indirect methods, which are not detrimental to the fish, although feeding history may affect the accuracy of the estimates.     

Effect of microbial phytase on apparent nutrient digestibility of barley, canola meal, wheat and wheat middlings, measured in vivo using rainbow trout (Oncorhynchus mykiss)

Microbial phytase (Natuphos 5000G) was supplemented into barley, canola meal, wheat and wheat middlings at 500 FTU kg^–1 diet to test the effectiveness of the phytase on digestibility of crude protein (CP), gross energy (GE) and minerals for rainbow trout. A total of 180 rainbow trout (initial mean body weight 223.8 ± 17.9 g) were stocked into ten 40-L fibreglass digestibility tanks with 18 fish per tank. Duplicate tanks were assigned to a reference diet and a single tank was assigned randomly to each of the eight diets made from these four ingredients supplemented with and without phytase. The collection of faeces lasted for 2 weeks. Faeces collected in each week represented a replicate and they were analysed separately. The mean apparent digestibility coefficients (average of four ingredients) in phytase supplemented and nonsupplemented ingredients were: CP, 97.3% and 96.5%; GE, 62.8% and 53.1%; calcium (Ca), 38.3% and –5.3%; magnesium (Mg), 72.4% and 50.3%; manganese (Mn), 31.0% and –4.2%; total-phosphorus (total-P), 71.1% and 47.6%; phytate-phosphorus (phytate-P), 87.5% and 22.3%; copper (Cu), 38.3% and 26.4%; potassium (K), 97.1% and 97.0%; sulphur (S), 90.2% and 88.6%; zinc (Zn), 12.3% and –16.6%. A two-tailed t -test indicated that phytase supplementation significantly ( P  < 0.05) improved the digestibility of Ca, Mg, Mn, total-P, phytate-P, and GE. The efficacy of phytase on nutrient digestibility also depended on the type of ingredient as measured in rainbow trout.     

Digestibility, growth and nutrient retention in rainbow trout (Oncorhynchus mykiss) fed diets extruded at two different temperatures

Digestibility and utilization of a fishmeal‐based diet extruded at 103 or 137 °C were examined. Each of the diets was fed to 0.5‐kg rainbow trout in nine tanks supplied with freshwater. Specific growth rate was significantly (P < 0.05) elevated for trout fed the feed extruded at 137 °C. The apparent digestibilities of protein and energy, feed conversion ratio, retentions of nitrogen and energy were not significantly affected by extrusion temperature. Digestibility of ash was significantly reduced in the diets produced at 137 °C.     

Growth, digestibility and nutrient utilization of rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax) juveniles fed different dietary soybean oil levels

A shortage of marine raw ingredients, such as fish oil, is predicted in the near future. The use of suitable alternative lipid sources, such as vegetable oils, is crucial for sustainable growth of the aquaculture sector. Three isonitrogenous (50% Crude Protein) and isoenergetic (19 kJ g⁻¹) diets, in which fish oil was gradually replaced by soybean oil (0, 25 and 50% of the oil fraction) were tested for 12 weeks, using European sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss) juveniles. No dietary effects (p>0.05) on growth performance, feed conversion, digestibility or body composition were observed with either species. The results obtained suggest the inclusion of soybean oil up to 50% of the dietary lipid is possible, in diets for sea bass and/or rainbow trout juveniles.     

Performance and immunological responses of rainbow trout (Oncorhynchus mykiss) fed bioprocessed plant‐based proteins

Marine‐derived fish meal (FM) is a traditional component of commercial aquaculture feeds for many farmed fish species. Modern bioprocessing technologies have been developed to produce high‐protein plant‐based ingredients for aquafeeds to further reduce FM and other conventional animal protein sources. A 90‐day feeding trial using juvenile rainbow trout (Oncorhynchus mykiss) (27.9 ± 1.4 g; mean ± SE) was completed to evaluate growth, feed efficiency, general health and immunological responses to diets containing experimental plant‐based protein sources and reduced FM. Trout were fed one of four dietary treatments: experimental bioprocessed soy protein concentrate (BSPC), commercially available enzymatically hydrolysed soy protein concentrate (CSPC), experimental bioprocessed barley protein concentrate (BBPC) and a FM control (FMC). At trial termination, there were no significant differences in relative growth (RG) or specific growth rate (SGR) between fish fed either FMC or BSPC (p > .05). Fish fed either CSPC or BBPC resulted in significantly lower RG and SGR than the FMC (p < .05). Significant respiratory burst analysis differences were observed among treatments at day 90 (p < .01), for fish fed either FMC or CSPC diets. This assessment of bioprocessed plant‐based protein ingredients facilitates the characterization and incorporation of bioprocessed soy and barley protein as the industry continues to evaluate FM replacements in rainbow trout feeds.     

Antioxidant‐related parameters,digestive enzyme activity and intestinal morphology in rainbow trout (Oncorhynchus mykiss) fry fed graded levels of red seaweed,Gracilaria pygmaea

This study was conducted to investigate the effects of dietary red seaweed, Gracilaria pygmaea level on growth, antioxidant‐related parameters, digestive enzyme activity and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fry. Five isocaloric and isonitrogenous diets were formulated to contain four G. pygmaea levels (30 (GL‐30), 60 (GL‐60), 90 (GL‐90) and 120 g/kg (GL‐120)), and a control diet was used, without inclusion of seaweed. Results of the feeding trial indicated that final body (FBW: 2.8–3.5 g) and specific growth rate (SGR: 4.8–5.2) were significantly improved when 60 g/kg G. pygmaea was supplemented in the diets. However, there was a significant reduction (p < .05) of final body weight (FBW) and specific growth rate (SGR) in fish fed 120 g/kg G. pygmaea. Protease activity was significantly lower in fish fed GL‐120 diet when compared to GL‐30 or control (p < .05). Lipase was significantly affected by dietary seaweed regardless its level of supplementation (p < .05). The inclusion of the Gracilaria in the diet led to evident changes in the fish antioxidant status with significant reduction of superoxide dismutase, glutathione peroxidase activity and lipid peroxidation products. The histological study demonstrated that all groups of fish displayed normal morphology of anterior intestine and pyloric caeca. Villi absorptive area in the anterior intestine of treatment groups GL‐90 and GL‐120 significantly decreased (p < .05). Overall, the results obtained in this study indicate that dietary G. pygmaea supplementation up to 90 g/kg improves growth performance in rainbow trout fry without compromising antioxidant responses and digestive function.     

Dietary probiotic Pediococcus acidilactici MA18/5M modulates the intestinal microbiota and stimulates intestinal immunity in rainbow trout (Oncorhynchus mykiss)

A study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 10⁶ CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p < .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout.     

Digestibility and growth performance of juvenile rainbow trout (Oncorhynchus mykiss) fed with pea and canola products

A digestibility experiment and subsequent 84-day feeding experiment evaluated the use of pea and canola meal products in diets for rainbow trout. The effect of milling and heat treatment on nutrient, dry matter and energy digestibility of raw/whole peas, raw/dehulled peas, extruded/dehulled peas and autoclaved air-classified pea protein was determined. Digestibility of the protein component was uniformly high for all pea ingredients (90.9–94.6%), regardless of the processing treatment. Autoclaving or extrusion increased starch digestibility by 41–75% ( P  ≤ 0.05), which consequently increased energy and dry matter digestibility of whole and dehulled peas. Autoclaved air-classified pea protein had superior protein (94.6%), energy (87.0%) and dry matter (84.0%) digestibility ( P  ≤ 0.05). It was demonstrated that inclusion of 25% dehulled peas, 20% air-classified pea protein or 20% canola meal fines was feasible in trout diets allowing for replacement of soya bean meal. The data showed no difference ( P  ≥ 0.05) in feed intake, final weight and specific growth rate (SGR) measurements, and feed utilization was not compromised with inclusion of pea or canola meal products as the primary plant ingredient. It was concluded that dehulled peas, air-classified pea protein and canola meal fines are suitable ingredients for use in trout diet formulation at a level of 20%.     

Androgen metabolism in the skin of the rainbow trout (Oncorhynchus mykiss)

Pieces of skin of male and female rainbow trout (Oncorhynchus mykiss) were incubated with testosterone and 11-ketotestosterone as substrates. In immature fish the conversion rate was low. In non-spawning adult males 11-ketotestosterone was reduced to 5α-11KDHT (up to 5.2%). In the fish in spawning condition the 5α-reduction rate was only about 1 to 2%. In the same specimens incubated with testosterone a high 11β-hydroxylase activity (23.8-25% in the male and 13% in the female skin) was found. Similar sex specific differences were observed for the occurence of 5α-reduced metabolites (about 20% in the male and 13% in the female tissue).

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Résumé Des fragments de peau de truites arc en ciel (Oncorhynchus mykiss, males ou femelles, ont été incubés avec de la testostérone ou de la 11-cétotestostérone, utilisées comme substrats. Chez les poissons immatures, les taux de conversion restent faibles. Chez les males adultes ne donnant pas de sperme, la 11-cétotestostérone est réduite en 5α-androstane-17β-ol-3,11-dione (jusqu'à 5.2%). Chezles poissons en conditions de fraie, le taux de 5α-réduction est seulement de l'ordre de 1 à 2%. Pour ce derniers individus, les incubations de peau en présence de testostérone montrent l'existence d'une forte activité 11β-hydroxylase (23.8-25% pour le male, et 13% pour la femelle). Des différences liées au sexe sont observées de la même manière dans la production de métabolites 5α-réduits (environ 20% avec le tissu male et 13% avect le tissu femelle).

     

Gut histology,immunology and the intestinal microbiota of rainbow trout,Oncorhynchus mykiss (Walbaum), fed process variants of soybean meal

Processed soybean meal ingredients have become an emerging plant‐based protein used in aquafeed formulations and have been shown to influence gastrointestinal health and microbiota in cultured species. Two 60‐day feeding trials with juvenile rainbow trout (Oncorhynchus mykiss, Walbaum) were conducted to compare the effects of fishmeal (FMC), defatted soybean meal (SBM), bioprocessed soybean meal (BSBM) and commercial soy protein concentrate (CSPC) ingredients on intestinal histology, innate immunity and microbiota profiles. Results indicated no significant differences in intestinal immunoglobulin concentrations (p = .41) or gut leukocyte phagocytosis at day 15 samplings (p = .41). Intestinal lysozyme content was found to be highest at day 60 in the BSBM treatment group (p < .01). No significant differences across treatments were observed in histological profiles at day 0 (p = .75), day 15 (p = .08) and day 60 (p = .22). ANOSIM analysis for microbiota beta diversity showed differences among all treatment groups, with the exception of the high and low levels of BSBM (p = .40). There were also differences observed in the alpha diversity ratios, with significant differences in gut communities among dietary groups as demonstrated by Chao‐1 (p < .01) and Shannon indices (p = .02). The incorporation of processed soy‐based proteins alters the microbial community composition within the distal intestine, and modulates lysozyme concentrations within the distal intestinal tissues.     

Growth performance,immune response and disease resistance of rainbow trout (Oncorhynchus mykiss) fed Thymus vulgaris essential oils

Efficacy of Thymus vulgaris essential oils was assessed on growth, immune response and disease resistance of rainbow trout (Oncorhynchus mykiss). Fish weighing 10 g were fed with dietary supplemented of the oils at 0.5, 1.0 and 2.0 ml/kg feed for 2 months. Fish fed with the oils at 0.5 ml/kg feed demonstrated a better weight gain and specific growth rate, compared to other treatments (p < .05). Fish fed with 1.0 ml the oils showed the highest up‐regulation of complement component 3 (C3) and (cluster of differentiation 4) (CD4) genes expression (p < .05), while lysozyme gene expression level significantly increased in fish fed with 2.0 ml of the oils. In addition, at the end of the experiment, the expression of C3 and CD4 genes were significantly up‐regulated in fish fed with 1.0 and 2.0 ml of the oils, while IL‐1ß and lysozyme genes expression levels were significantly decreased in fish fed 2.0 ml oils, towards the end of the trial (p < .05). There was a fluctuation in the levels of Alanine aminotransferase, Aspartate aminotransferase and Alkaline phosphatase in all treatments during the experiment. When treated fish were challenged with Aeromonas hydrophila, the highest survival rate was observed in 0.5 ml/kg treatment, followed by 2 and 1 mg/kg treatments. Overall, these findings demonstrated that dietary administration of T. vulgaris oils especially at 0.5 mg/kg feed can be considered as a potential component for enhancing of the growth, immune responses and disease resistance of trout against motile Aeromonas septicemia caused by A. hydrophila.     

Apparent digestibility comparison in rainbow trout (Oncorhynchus mykiss) assessed using three methods of faeces collection and three digestibility markers

Experiments were undertaken to investigate the apparent digestibility coefficient (ADC) of a range of macro- and micronutrients in rainbow trout using three external digestibility markers (chromic oxide, acid insoluble ash and titanium dioxide, alone or in combination), and three methods of faeces collection (modified Guelph system, St-Pee system and abdominal massage; hereafter referred to as 'column', 'collect' and 'strip', respectively). For each method of faeces collection, three replicate tanks of fish were acclimated for 5 days to a practical diet containing the external marker followed by 5 days of faeces collection. Both marker type and collection method significantly influenced ADC estimate in a similar manner for dry matter, protein, nitrogen-free extract, ash and energy. The ADC was consistently highest for the column and lowest for the strip methods of collection, and titanium dioxide gave higher ADCs vs. the other markers. Lipid ADC did not differ between the column and collect methods, but collection of faeces by the strip method gave lower ADCs, irrespective of marker type. In general, nutrient ADC was higher with the combined markers than when single markers were employed. The influence of marker type and collection method was less clear for the individual minerals studied.     

Growth performance,nutrient digestibility and lipase activity in juvenile rainbow trout (Oncorhynchus mykiss) fed fat powder in diet containing emulsifiers (cholic acid and Tween‐80)

This research was conducted to investigate the effects of two dietary emulsifiers on nutrient digestibility and lipase activity in rainbow trout (Onchorhyncus mykiss). A basal rainbow trout diet containing fat powder supplemented with 10 and 5 g kg^?1 of cholic acid, and 20 and 40 g kg^?1 of Tween‐80. Control diet contained no emulsifiers with fat powder was replaced by fish oil. Each diet was randomly assigned to 1,500‐L tanks in triplicate. Juvenile rainbow trout with an initial weight of 27.32 ± 2.03 g were randomly distributed in the experimental tanks. The results showed that growth parameters did not change by the addition of the two emulsifiers (p > .05). Total triglyceride content was significantly higher in control fish fed diet containing fish oil (p < .05), while serum cholesterol content showed no significant differences among treatments (p > .05). Control diet resulted in a higher fat digestibility than those of other experimental diets. However, protein and ash digestibilities in diet containing emulsifier were higher than those of the control diet. Control group showed the lowest lipase activity, whereas 20 g kg^?1 Tween‐80 diet caused the highest lipase activity among treatments (p < .05). In conclusion, it seems that a higher lipase activity induced by the emulsifiers could not compensate for the negative impacts of fat powder on the experimental diets.     

Using Near Infrared Reflectance Spectroscopy (NIRS) to predict the protein and energy digestibility of lupin kernel meals when fed to rainbow trout,Oncorhynchus mykiss

This study examined the potential of using near infrared spectroscopy (NIRS) to predict the nutrient composition, energy density and the digestible protein and digestible energy values of lupin kernel meals when fed to rainbow trout. A series of 136 lupin kernel meals were assessed for their protein and energy digestibilities using the diet‐substitution approach in a series of 10 experiments over a 6‐year period from 2002 to 2008. Two reference diets were also included in each experiment. Minimal variance in the digestibility parameters of both reference diets was observed among the experiments ensuring that there was a high degree of robustness in the across‐experiment evaluations. The same lupin kernel meal samples were also scanned using a diode array near infrared spectrophotometer (DA‐NIRS). The spectra obtained by the DA‐NIRS were chemometrically calibrated against both the chemical composition and the digestible value data using multivariate analysis software. The cross validation tests used in this study provide a valid indication of the potential to predict the nutrient composition, energy value and digestible protein and energy values of the lupin kernel meals as used in diets for rainbow trout. That the standard errors of cross validation (SECV) of the parameters investigated were generally commensurate with the cross trial variation seen in the reference sample indicating robust calibrations for the two target parameters of digestible protein and digestible energy. Therefore this study demonstrates that within one raw material type that not only does significant variability in the digestible value of the raw materials exist, but that it is possible to use NIRS technology to provide rapid estimates of the digestible value of those raw materials in near real‐time.     

Apparent digestibility coefficients of nutrients in brewer's and rendered animal by-products for rainbow trout (Oncorhynchus mykiss (Walbaum))

Two experiments were conducted to measure the apparent digestibility coefficients (ADCs) of nutrients, dry matter, and energy in by‐products of the brewing industry and in selected animal protein ingredients for rainbow trout. In experiment 1, 500 rainbow trout (average body weight 170.8±5.5 g) were stocked in ten 140‐L digestibility tanks with 50 fish per tank and two tanks per diet. Yttrium oxide was used as an inert marker in the diets. The high fibre content of brewer's dried grains (BDG) affected the ADCs of dry matter but not of protein or amino acids. Brewer's dried yeast had a higher protein content than BDG, but ADC values for protein and amino acids were significantly lower. The ADCs of phosphorus were similar among brewer's dried products. The BDG high‐protein, fraction had marginally higher ADC values for dry matter, protein and amino acids than regular BDG. Conditions in experiment 2 were similar to those in experiment 1. ADC values for spray‐dried porcine plasma were over 98% for dry matter, crude protein, crude fat, and gross energy. ADC values for spent hen meal were higher than those of poultry by‐product meal or feather meal, with the exception of gross energy. However, spent hen meal was unpalatable. The ADCs in these ingredients were variable, and this variability must be taken into account when these ingredients are formulated into feeds for fish.     

Effects of inulin and fructooligosaccharides on growth performance,body chemical composition and intestinal microbiota of farmed rainbow trout (Oncorhynchus mykiss)

The objectives of the present study were to investigate the effects of inulin and fructooligosaccharides (FOS) on growth performance, whole body and fillet chemical composition and intestinal microbiota of rainbow trouts reared under fish farming conditions. Trouts fed inulin‐ or FOS‐containing diets (5 and 10 g kg^?1) exhibited significant (P = 0.030) body weight gain improvements compared with controls. An increase in gross energy (P = 0.044) and Ca content (P = 0.034) in the whole body of trouts was observed for prebiotic treatments. A decrease in crude protein content (P = 0.009) and a tendency to increase total lipid and gross energy contents (P = 0.090 and P = 0.069, respectively) were detected in the fillet tissue for prebiotic treatments. These results clearly indicate that inulin and FOS improved the intestinal absorption of Ca and that the increased amount was predominantly incorporated into bone tissue. Inulin reduced (P = 0.027) the intestinal population of Vibrio spp. in the distal region to such an extent that no viable counts were detected. The presence of Flavobacterium spp. was not detected in any group, and the numbers of Aeromonas spp., Pseudomonas spp. and Gram‐positive bacteria were not affected (P > 0.05).     

Effect of enzyme supplementation to dehulled lupin-based diets on growth, feed efficiency, nutrient digestibility and carcass composition of rainbow trout, Oncorhynchus mykiss (Walbaum)

High inclusion levels of dehulled lupin (Lupinus angustifolius) in salmonid diets significantly decrease growth rates. This may be caused by the high concentrations of non‐starch polysaccharides including oligosaccharide (OS) in lupin. The antinutritive effects of OS have not yet been fully investigated in fish. The objective of this study was to determine the effect of enzyme supplementation of dehulled lupin‐based diets on the fish performance. There were two control diets: a fish meal‐based diet with no plant protein (FM) and a diet that contained 50% dehulled lupin (L). Four experimental diets based on diet L and containing four different exogenous enzyme supplements were used: diet L(E) (Energex^™); diet L(B) (Bio‐Feed^™ Pro); diet L(α) (Alpha galactosidase^™); and diet L(Mix), which contained all the enzymes. Fish were randomly stocked into tanks in duplicate groups of 38 fish, 16.58±0.169 (SE) g, and were fed twice a day for 6 weeks. The supplemented enzymes did not improve weight gain in fish fed lupin‐based diets. However, mixed enzyme significantly improved Protein Efficiency Ratio (PER). Apparent digestibility of DM, CP and GE significantly improved in fish‐fed L(E) diet. None of the supplemented enzymes affected digestive tract indices or carcass composition. Surprisingly, weight gain was significantly higher in fish‐fed L(α), L(E) and L(Mix) diets as compared with FM diet. Feed intake was significantly higher in fish‐fed L, L(α) and L(E) diets compared with the FM diet. It is concluded that storing of lupin kernel under a suitable condition may have partially hidden the positive effects of exogenous enzymes through activating the endogenous enzymes.     

An in vitro method to determine phosphorus digestibility of rainbow trout Oncorhynchus mykiss (Walbaum) feed ingredients

An in vitro method was developed to assess the digestibility of phosphorus in 12 plant and animal feed ingredients for rainbow trout Oncorhynchus mykiss (Walbaum). The method simulates the gastrointestinal tract of the rainbow trout with regard to pH and gastrointestinal enzymes. Phosphorus solubility was measured after acid digestion (pH 3) with and without gastric enzymes, after alkaline digestion (pH 9) with and without intestinal enzymes, and after a two-step process involving acid and alkaline digestion. Commercially available digestive enzymes from mammals were compared with digestive enzymes from rainbow trout. Correlating in vitro digestibility with in vivo digestibility showed that acid digestion with both commercial enzymes ( r ²=0.98, P  < 0.05) and trout enzymes ( r ²=0.94, P  < 0.05) predicted the in vivo digestibility of animal feed ingredients. Alkaline digestion with both enzyme systems (commercial r ²=0.79; trout r ²=0.74, P  < 0.05) or without ( r ²=0.82, P  < 0.05) enzymes predicted the in vivo digestibility of ingredients from animal byproducts but not those from plant products. The in vitro digestibility with two enzyme steps (acid and alkaline) predicted in vivo digestibility of plant and animal ingredients ( r ²=0.79 for commercial enzymes and r ²=0.74 for trout enzymes) better than did one-step acid or alkaline digestion.