Replacement of fishmeal by canola protein concentrate in diets fed to rainbow trout (Oncorhynchus mykiss)

A dephytinized protein concentrate prepared from canola seed (CPC) was assessed for nutrient digestibility and performance in rainbow trout (Oncorhynchus mykiss). The apparent digestibility coefficients of CPC were: dry matter, 817 g kg^?1; crude protein, 899 g kg^?1; gross energy, 861 g kg^?1; arginine, 945 g kg^?1; lysine, 935 g kg^?1; methionine, 954 g kg^?1; threonine, 893 g kg^?1. A 9‐week performance trial assessed 7 diets. Fishmeal provided 940 g kg^?1 of the protein in the control diet. Test diets consisted of CPC or water‐washed CPC replacing 500 and 750 g kg^?1 of fishmeal protein; and CPC plus an attractant replacing 500 and 750 g kg^?1 of fishmeal protein. No significant differences in performance were observed (P > 0.05). A subsequent 9‐week performance trial evaluated the effect of adding CPC into compound diets containing fishmeal/soybean meal/corn gluten meal. Five diets were prepared: fishmeal provided 670 g kg^?1 of the protein in the control diet, in the remaining diets CPC was incorporated into commercial‐like trout diets at 100, 200 and 300 g kg^?1 replacement of fishmeal protein, the fifth diet included an attractant in the 300 g kg^?1 replacement diet. No significant differences in performance were obtained (P > 0.05). These studies show that dephytinized canola protein concentrate has potential to replace substantial levels of fishmeal in diets for carnivorous fish without compromising performance.     

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%.     

Effects of extrusion processing of feed ingredients on apparent digestibility coefficients of nutrients for rainbow trout (Oncorhynchus mykiss)

An experiment was conducted to evaluate the effects of extrusion processing on apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude fat, energy and minerals in soya bean meal (SBM), barley, corn gluten meal and whole wheat, using rainbow trout Oncorhynchus mykiss as the test species. In addition, availabilities of amino acids were also determined in SBM. Feed ingredients were preconditioned at 89–93 °C and then extruded using a Wenger X‐85 extruder. Nonextruded ingredients were used as is, meaning that they were not preconditioned. The extruded and nonextruded ingredients were mixed with a casein–gelatin reference diet at 3 : 7 ratio prior to determination of ADC values. A total of 135 trout (initial mean body weight 223.4 ± 12.7 g) were stocked into nine 140‐L fibreglass digestibility tanks with 15 fish per tank. Individual tanks were assigned randomly to each of eight diets made from the four ingredients (extruded and nonextruded) plus the reference diet. After faeces were collected in the first week, the diets were switched among tanks, and faeces were collected again after 5‐day acclimation period in the second week. Yttrium oxide was used as the inert marker. Results showed that extrusion processing significantly improved ADCs of dry matter, crude fat and gross energy, and reduced ADCs of crude protein, phosphorus, copper, iron and zinc. Results also showed that the effects of extrusion processing on chemical composition and ADCs of nutrients depended on the ingredients. It is recommended that trace minerals such as copper, iron and zinc be supplemented by an additional 10–20% when rainbow trout diets are extruded because of their reduced bioavailability in plant meal‐based feed ingredients.     

Apparent digestibility of nutrients and energy in extruded diets from cultivars of barley and wheat selected for nutritional quality in rainbow trout Oncorhynchus mykiss

A digestibility trial was conducted to elucidate potential differences in barley ( Hordeum vulgare L.) lines and varieties as a first step in defining their potential for use in aquafeeds. A diverse group of six barley lines having six combinations of selected attributes, normal versus low phytic acid, normal versus waxy, and hulled versus hull-less, were chosen for evaluation along with a waxy wheat ( Triticum aestivum L.) and soft white wheat. The experimental diets were manufactured by cooking extrusion and consisted of a 70% reference diet that was formulated to contain a minimal level of phosphorus and 30% test ingredient. Phosphorus availability ranged from 17 to 78% and was influenced by starch type in wheat. Apparent protein digestibility ranged from 53 to 125% and differences were observed between wheat varieties based on starch type. Apparent energy digestibility ranged from 32 to 63%, with waxy barley varieties having higher energy digestibility coefficients than normal starch varieties. Waxy starch varieties had higher starch digestibility in both barley and wheat because of the greater digestibility of amylopectin than amylose. In summary, the higher energy digestibility of waxy barley lines suggests that these varieties warrant further attention as feed ingredients for rainbow trout.     

Identification of a novel gill-specific calpain from rainbow trout (Oncorhynchus mykiss)

Calpains are calcium-dependent neutral proteases responsible for many cellular functions. The two forms of calpain ubiquitously expressed in mammalian tissues are known as μ-calpain and m-calpain. We report here the identification of a novel calpain that is similar to but distinct from the μ- and m-calpains in rainbow trout. The cDNA of the novel gene is 2623 bp in length with a single open reading frame. The predicted protein (676 amino acids) contains the conserved calpain characteristic domains that include: domain I (pro peptide), II (cysteine catalytic site), III (electrostatic switch), and IV (calmodulin-like) with five Ca²⁺-binding EF hands. Northern blot and RT-PCR analyses demonstrated that the novel calpain gene is predominantly expressed in rainbow trout gills. Comparison of the novel protein with the ubiquitously expressed calpains and several mammalian tissue-specific calpains revealed that the novel calpain is an orthologue of the mammalian digestive tract specific calpain (calpain 9).     

The degree of carotenoid esterification influences the absorption of astaxanthin in rainbow trout, Oncorhynchus mykiss (Walbaum)

The absorption of astaxanthin from diets (30 mg kg^?1 inclusion) supplemented with either unesterified astaxanthin; isolated astaxanthin monoesters, diesters or a cell‐free carotenoid extract from Haematococcus pluvialis were studied in rainbow trout (>200 g). No significant differences (P > 0.05) were recorded in the apparent digestibility coefficients (ADC) (≈60–65%) between astaxanthin sources. However, following consumption of a single meal, peak serum astaxanthin levels at 32 h (≈1.0–1.6 μg mL^?1) were significantly higher (P < 0.05) in fish fed unesterified astaxanthin and astaxanthin monoester, compared to fish fed astaxanthin diester and the cell free extract. However, no significant differences (P > 0.05) were recorded in serum astaxanthin uptake rates between sources of astaxanthin. Results suggest that the extent of carotenoid esterification negatively influences the peak serum levels of astaxanthin in rainbow trout.     

Relationships between growth and disease resistance in rainbow trout,Oncorhynchus mykiss (Walbaum)

Rainbow trout from 23 families were evaluated for growth and resistance to the bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum and infectious haematopoietic necrosis (IHN) caused by IHN virus. Average family weights were between 161 and 263 g with an average of 225 g at 213 days post‐fertilization with specific growth rates ranging from 2.37 to 2.88. Per cent survival of fish challenged with F. psychrophilum was between 18% and 100%, while for those challenged with IHNV, the range was between 12% and 93%. Significant positive correlations were found for end body weight and resistance to IHN (P < 0.05) and for early body weight and resistance to BCWD (P < 0.1). However, no significant correlations were detected between resistance to both pathogens or disease resistance and overall genetic diversity or diversity within the major histocompatibility locus.     

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

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

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.     

Mineral availability from barley low phytic acid grains in rainbow trout (Oncorhynchus mykiss) diets

Phosphorus storage within plant seeds occurs mainly as phytic acid, which has profound implications on the use of seeds as food material. Phytic acid phosphorus is unavailable to non‐ruminants, leaches ionic minerals during digestion, and is excreted at elevated levels as a waste product. This presents a problem in nonruminant livestock production including current efforts to develop renewable grain and legume products for use in fish feeds. The development of lines of several cereal grain species that have reduced seed phytic acid concentration provides a novel approach to dietary and environmental problems associated with seed phytic acid. Utilizing four isogenic strains of barley (one normal for seed phytic acid, and three low phytic acid lines that produce seeds with approximately 50, 70 and 95% reductions in phytic acid) the apparent digestibility of nutrients in formulated diets containing these barleys at a level of 30% was measured using rainbow trout (Oncorhynchus mykiss). Also examined was the apparent availability of several minerals including phytate phosphorus and total phosphorus. Results from these studies corresponded well with the results of other animal studies that evaluated low phytic acid cereal grains. With increasing reductions in seed phytic acid, seed available phosphorus increased and faecal phosphorus was reduced by up to 50%. Calcium availability increased, copper and sulphur decreased, and the other tested minerals demonstrated either increased or decreased availability in a manner uncorrelated to grain phytic acid concentration.     

Effects of dietary Camelina sativa products on digestible nutrient compositions for rainbow trout (Oncorhynchus mykiss)

Two trials were conducted to determine the effect of dietary inclusion of camelina (Camelina sativa) products on their digestible nutrient compositions in rainbow trout. In the first experiment, the following camelina products: full‐fat seed, oil, high‐oil residue meal (HORM), pre‐press solvent‐extracted meal (SECM) and toasted SECM were evaluated. In the second trial, the utilization of SECM, SECM soaked in water (WS), SECM treated with a multicarbohydrase, Superzyme?‐OM, SECM treated with Bio‐Phytase and SECM treated with Superzyme?‐OM and Bio‐Phytase (MIX) was determined. The experimental diets consisted of a basal diet and test ingredient with a ratio of 70:30, except for camelina oil where the ratio was 80:20. In Experiment 1, SECM had the highest level of digestible crude protein (352 g kg^?1), whereas the oil was the best source of digestible energy (8,063 kcal kg^?1) and digestible crude fat (908 g kg^?1). In Experiment 2, there were no significant differences in nutrient digestibility of SECM and HORM; however, WS and MIX had significantly more digestible dry matter and digestible crude fat than SECM and HORM. Camelina by‐products have the potential to replace fishery by‐products in rainbow trout feeds.     

Effects of canola meal on physiological and biochemical parameters in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (initial body weight 4.16 ± 0.25 g) were fed diets [crude protein 420 g kg^?1; gross energy 18.7 MJ kg^?1 dry matter (DM); crude fat 110 g kg^?1] containing graded levels of either a canola meal (crude protein 350 g kg^?1 DM) supplemented with DL‐methionine as partial fish meal protein. A growth trial was conducted over 16 weeks at a water temperature of 12 ± 1 °C. At the end of the growth trial, in addition to body composition analyses, plasma tri‐iodothyronine (T₃) and thyroxine (T₄), cholesterol and liver fatty acid composition were measured. Replacement of fish meal with canola meal (100–570 g kg^?1 replacement) did not affect on growth performance. At 16th week, plasma cholesterol levels were reduced in fish fed all diets in comparison with 8th week. Plasma T₄ levels were significantly higher in the canola meal‐fed fish sampled after 16 weeks, but no significant differences in T₃ levels were obtained (P > 0.05). Proximate compositions were affected by dietary treatments. The liver fatty acid composition reflected that of the diet with a higher level of polyunsaturated (n‐6) fatty acids in fish fed diet canola meal and a higher content in n‐3/n‐6 ratio in fish fed diet without canola meal. These studies show that canola meal has potential to replace substantial levels of fish meal in diets for carnivorous fish without compromising performance.     

Supplementing enzymes to extruded,soybean‐based diet improves breakdown of non‐starch polysaccharides in rainbow trout (Oncorhynchus mykiss)

Plant‐based feed ingredients typically contain remnants of dietary fibres [DF; non‐starch polysaccharides (NSP) and lignin] that have various antinutritive effects in carnivorous fish. Exogenous enzymes have been shown to improve the apparent digestibility coefficients (ADC) of plant‐based diets presumably by assisting in the breakdown of NSP. This study examined the effects on NSP degradation when supplementing β‐glucanase, xylanase, protease or a mix of the three enzymes to an extruded, juvenile rainbow trout (Oncorhynchus mykiss) diet containing 344 g kg^?1 de‐hulled, solvent‐extracted soybean meal (SBM). The NSP content in the non‐supplemented control diet and in faecal samples from the dietary treatment groups was analysed to determine the recovery/apparent digestibility of cellulose and total non‐cellulosic polysaccharide (T‐NCP) sugar monomers. The enzymes had significant, positive effects at the pH range and temperature prevailing in the gastrointestinal tract: β‐glucanase improved the ADC of mannose, galactose and uronic acids; xylanase and protease improved the ADC of xylose; and protease furthermore improved the ADC of mannose and uronic acids. There were no effects when supplementing all three enzymes together. In conclusion, exogenous enzymes may potentially be applied to fish feed containing SBM, assisting in the breakdown of NSP and alleviating some of the antinutritive effects.     

Dietary formic acid enhances apparent digestibility of minerals in rainbow trout, Oncorhynchus mykiss (Walbaum)

The effect of dietary formic acid on the availability of phosphorus (P) from a fishmeal-based diet by rainbow trout, Oncorhynchus mykiss (Walbaum), reared in brackish water (5–6 g L⁻¹) was determined. Diets containing a low amount of P (6.0 mg P g⁻¹ dry matter) were acidified with 0, 4 and 10 mL kg⁻¹ formic acid and fed to trout (average weight, 520 g) for 4 weeks. The measured pH of the diets were 6.3, 5.8 and 5.3, respectively. The intestinal solubility of P and the digestibility of P were measured by stripping the faecal matter from the fish. The apparent digestibility coefficient (ADC) of P significantly ( P < 0.05) increased from 69.5% to 75.0% of the basal diet in fish fed diets containing 10 mL kg⁻¹ formic acid. The solubility of P in the intestine was highly variable within each treatment, and the differences were not significant. The pH of intestinal content increased with the increase in dietary formic acid concentration. The ADC of magnesium and calcium also showed a significant ( P < 0.05) increase with the acidification of diet by formic acid.     

Digestibility, growth and excretion response of rainbow trout (Oncorhynchus mykiss Walbaum) to feeds of different ingredient particle sizes

The effects of feed ingredient particle size on apparent digestibility, growth and excretion responses of rainbow trout were investigated in pilot production systems. Particle size of the feed ingredients (ground using a hammer mill with 0.6 and 3.0 mm screen sizes) had no significant effect (P > 0.05, d.f. = 1/6) on the apparent digestibility of dry matter, phosphorus and crude protein in cold‐extruded diets. Feed ingredient particle size had an impact on the feed conversion ratio over an 85‐day feeding trial when key ingredients (78.65% of diet) were ground using a pulverizer and a hammer mill with 3.0 mm screen size and heat extruded. No significant differences (P > 0.05, d.f. = 1/12) were observed in the excretion ratios of TAN (total ammonia nitrogen), TKN (total Kjeldahl nitrogen), TP (total phosphorus), BOD₅ (5‐day biochemical oxygen demand) and TSS (total suspended solids) among three feed types, which included a wide ingredient particle size distribution.     

Supplementing rainbow trout (Oncorhynchus mykiss) broodstock diets with choline and methionine improves growth in offspring

Nutritional programming represents the mechanism through which broodstock feeding strategies have lifelong effects on the offspring generation. The objective of this study was to determine whether supplementing rainbow trout, Oncorhynchus mykiss broodstock diets with choline and methionine affects offspring growth performance. Experimental diets were produced by top-dressing a commercial broodstock diet with (a) 12,000 ppm methionine, (b) 7,400 ppm choline, (c) 12,000 ppm methionine and 7,400 ppm choline, or (d) water (control). Six rainbow trout families were fed experimental diets beginning 18 months post-hatch through spawning; the offspring consumed a commercial diet. The broodstock diet did not affect maternal body weight, body condition, egg size, or egg yield (p > .05). Eggs from choline-treated broodstock contained 10% more choline than control eggs (p < .05). Offspring from choline-treated broodstock were smaller than controls at 146 days post-hatch (dph) (p < .05). At the final harvest (439 dph), offspring from the control broodstock weighed 12–18% less than offspring from broodstock consuming the supplemented diets (p < .05). However, there was a significant diet-by-family interaction on offspring growth (p < .05); supplemented diets improved performance in three of the six broodstock families. These findings indicate that supplementing broodstock diets with methionine and choline causes a nutritional programming effect that benefits growth in offspring.     

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.     

Metabolism of exogenous histamine in rainbow trout (Oncorhynchus mykiss)

Information on the metabolism of exogenous histamine in fish is of much concern regarding the effect of dietary histamine on fish. Histamine catabolic enzymes, diamine oxidase and histamine N-methyl transferase were measured in the tissues of rainbow trout. Diamine oxidase was detected in the stomach, pylorus caeca and intestine. Histamine N-methyl transferase was detected only in the liver.A change in the contents of histamine and its metabolites was observed in the tissues of rainbow trout after oral administration of histamine. A large amount of imidazole acetic acid was observed in the serum, kidney, liver and muscle. On the other hand, 1-methyl histamine was detected only in the liver. Histamine and its metabolites, imidazole acetic acid and 1-methyl histamine were metabolized and diminished within 48 hr in all tissues.These results showed that histamine was metabolized by two metabolic routes in rainbow trout. One is the main pathway producing imidazole acetic acid by intestinal diamine oxidase and the other is the complementary pathway producing 1-methyl histamine by liver N-methyl-transferase.     

Supplementation of maca (Lepidium meyenii) tuber meal in diets improves growth rate and survival of rainbow trout Oncorhynchus mykiss (Walbaum) alevins and juveniles

Maca tuber meal is used in fish diet formulations in Andean trout culture and knowledge of its effects on fish growth is paramount to healthy human food production. In the first experiment with rainbow trout alevins (0.096±0.002 g), starter diets were offered from first feeding until 15 weeks. We formulated high protein content (～60%) semi‐purified starter diets supplemented with 0%, 5%, 10%, or 15% maca tuber meal (control, M‐5, M‐10, and M‐15 respectively). The second feeding trial was conducted with juveniles (1.56±0.02 g) fed one of three diets (control, M‐15, and commercial) for 8 weeks. In the first experiment, fish fed M‐10 and M‐15 diets exhibited significantly higher growth rates than the other dietary groups. Survival was significantly improved in the groups fed diets supplemented with maca tuber meal (60.0–69.2%) in comparison with the group fed a control diet (21.7%). The second experiment showed a higher growth rate in the M‐15 group compared with the control and a commercial diet fed group. Leucocyte numbers were increased by dietary supplementation of maca tuber meal. The findings of the present study suggest that a maca tuber meal inclusion at least 5% improves growth rate, feed utilization, immunity by increased leucocyte number, and survival of rainbow trout alevins and juveniles.