Faye M. Dong

Apparent protein digestibility and mineral availabilities in various feed ingredients for salmonid feeds

Apparent digestibility of protein and availability of minerals (Ca, K, P, Mg, Na, Cu, Fe, Mn, Sr, Zn) in various feed ingredients were determined for coho salmon and rainbow trout using yttrium oxide (Y2O3) as the inert marker and passive feces collection tanks. The feed ingredients were herring meal, menhaden meal, anchovy meal, deboned whitefish meal, poultry by-product meal, feather meal, soybean meal, corn gluten meal, wheat gluten meal, wheat middling and wheat flour. Apparent digestibility (%) of protein and availability (%) of minerals were determined as a fractional net absorption of nutrients from diets. Apparent digestibility of protein and availability of K was high (>80%) in all feed ingredients, whereas digestibility of dry matter and availability of Ca, Cu, Fe, Mg, Mn, Na, P, Sr and Zn were variable among ingredients. Apparent availability (%) of mineral elements was not significantly correlated to the amount of nutrient intake (μg nutrient g−1 BW day−1) in any test diet. Net nutrient absorption (μg g−1 BW day−1) was positively correlated (P<0.05) to the nutrient intake except for Mn, Fe and Ca. Fecal nutrient losses (μg g−1 BW day−1) were positively correlated (P<0.05) to nutrient intake except for protein, Na, K and Zn.

Metabolic response to dietary phosphorus intake in rainbow trout (Oncorhynchus mykiss)

Abstract The objectives of this study were to determine which indicators were most responsive to suboptimal phosphorus intake in fingerling rainbow trout, and to observe the magnitude of these changes over time. Fish with an initial mean weight of 1.8 g were hand-fed one of five semipurified wheat-gluten based diets containing between 0.23%–1.16% dietary phosphorus, or a fish meal control diet (1.8% P) for 8 weeks. Phosphorus, calcium and magnesium concentrations in whole body, skin (with scales), and plasma were measured bi-weekly. Alkaline phosphatase activity was determined in plasma and in a crude intestinal homogenate. There was no correlation between dietary phosphorus concentration and body weight of rainbow trout. Of all tissues and metabolites examined, skin was the most responsive to differences in dietary phosphorus concentration. Dietary treatment had a significant effect on the concentrations of ash, phosphorus, calcium and magnesium in rainbow trout skin at weeks 4 and 8. Whole body ash, phosphorus, calcium, and magnesium concentrations were also highly responsive to graded levels of dietary phosphorus at week 8. Rainbow trout fed suboptimal phosphorus diets had significantly lower plasma phosphorus concentrations and alkaline phosphatase activity, and significantly higher whole body lipid than those fed adequate phosphorus diets. Alkaline phosphatase activity of the intestinal homogenate was not significantly correlated with dietary phosphorus intake.

Fish performance, fillet characteristics, and health assessment index of rainbow trout (Oncorhynchus mykiss) fed diets containing adequate and high concentrations of lipid and vitamin E

The recent trend for rainbow trout feeds to be higher than 15% lipid may improve feed conversion ratios (FCRs) and increase the lipid concentration of the fish. However, one disadvantage of the higher lipid concentration in fish is the potential for increased rates of lipid oxidation, which could affect fish health and contribute to off-flavors in fillets. The objective of this experiment was to determine the effects of adequate and high concentrations of dietary lipid and the antioxidant vitamin E on fish performance, fish health, and fillet product quality of rainbow trout. A 10-week feeding trial was conducted with diets containing either 15 or 30 g lipid/100 g feed, and either 300 (e) or 1500 (E) mg dl-α-tocopheryl acetate/kg feed (15e, 15E, 30e, and 30E). Fish fed 30% lipid diets had significantly higher final body weight, specific growth rate (SGR), and protein efficiency ratio (PER) than fish fed 15% lipid diets. All health parameters of fish measured in the experiment were within normal ranges of healthy fish although several parameters were affected by increasing dietary lipid concentration. Lipid concentration in fish body (whole body, fillets, and viscera) reflected dietary lipid concentration. Increasing the lipid concentration in the feed from 15% to 30% increased the fillet lipid concentration from 8.4 to 9.6 g lipid/100 g fillet. Vitamin E concentrations in fillets reflected dietary vitamin E concentration and ranged from 8.3 mg/kg (30e) to 49.1 mg/kg (15E) (P<0.05). Fish fed the 30% lipid diets had significantly higher concentration of malonaldehyde [thiobarbituric acid reactive substances (TBARS)] in fillets than fish fed the 15% lipid diets, and fish fed the “E” diets had significantly lower concentration of malonaldehyde in fillets than fish fed the “e” diet. Principal components analysis of sensory evaluation results showed that the 30e fillet had higher scores than other treatments on a “fishy” axis, which was highly correlated with overall flavor intensity, fishy, musty, sour, and bitter attributes. “Fishy” scores of the 30E fillets were lower than the 30e fillets, and were comparable to those of the 15e fillets. These results suggested that increasing the concentration of vitamin E in the feed from 300 to 1500 mg/kg could reduce the “fishy” aroma in fillets of trout fed a 30% lipid diet.

Availability of phosphorus and trace elements in low-phytate varieties of barley and corn for rainbow trout (Oncorhynchus mykiss)

Approximately two-thirds of phosphorus in various grains is present as phytate, which is not well-utilized by fish and other monogastric species. Besides its low availability of phosphorus, phytate is reported to reduce the availability of other dietary nutrients to animals. Single-gene, non-lethal low phytic acid (lpa) mutations in corn and barley cause the seed to store most of the phosphorus as inorganic phosphorus instead of as phytate phosphorus. Theoretically, using these mutant grains containing lower levels of phytate in animal feeds should reduce phosphorus excretion by the animals, provided that available phosphorus levels in feeds containing these grains are appropriately adjusted downward. This study was conducted as a first step to determine if the biological availability of phosphorus in the low-phytate mutants of barley, dent corn and flint corn differed significantly from that in ordinary grains for fish. Also of interest was the effect, if any, on the availability of other minerals in formulated feeds containing the low-phytate grains. Feeding trials demonstrated that the apparent availability of phosphorus in low-phytate grains was significantly higher than that in ordinary grains when they were combined with low-ash ingredients. Fecal phosphorus content (on average) decreased 50.2% (in phytate-phosphorus) or 42.9% (in total phosphorus) by replacing ordinary grains with low-phytate grains in the low-ash diets. The apparent availabilities of calcium, iron, zinc and strontium also were significantly higher in the low-ash diet containing low-phytate dent corn than that containing ordinary dent corn. However, no such increase was observed with low-phytate barley or low-phytate flint corn over their counterpart grains in either calcium, iron or zinc. The apparent availabilities of copper, manganese, magnesium, potassium and sodium were not significantly different between ordinary and low-phytate grains. The apparent digestibility of dry matter also was not significantly different between ordinary and low-phytate grains. The results of this study suggest that a substantial reduction of phosphorus discharge from fish, poultry and animal farms could be achieved simply by replacing ordinary grains with low-phytate mutant grains in low-ash feeds.

Effects of dietary supplements on the availability of minerals in fish meal; preliminary observations

Abstract Preliminary studies were conducted to determine if several feed supplements with the potential to improve dietary mineral availabilities in fish meal had any measurable effect in fish feeds. In the first study with rainbow trout, 11 supplements were tested: citric acid; sodium citrate; potassium chloride; sodium chloride; histamine dihydrochloride; EDTA disodium salt; sodium bicarbonate; a mixture of amino acids; ascorbic acid; a mixture of inositol and choline; and cholecalciferol. Apparent availability of calcium, phosphorus, magnesium, sodium, iron, manganese and strontium in fish meal-based diets was determined using both yttrium oxide (Y2O3) and chromium oxide (Cr2O3) as inert dietary markers. Apparent availability was expressed as the fractional net absorption (%) of minerals from diets. After a 7-day acclimation period with test diets, fecal samples were collected for five consecutive days using passive collection systems. Apparent availability of calcium, phosphorus, magnesium, iron, manganese and strontium was increased by citric acid supplementation. Apparent availability of manganese also was increased by EDTA and sodium citrate. The other supplements had no measurable effect on the apparent availability of minerals in fish meal. In the second study, the effect of supplemental citric acid was further investigated using monogastric (rainbow trout) and agastric fish (goldfish). Fish were fed for 5 weeks (rainbow trout) or 3 weeks (goldfish) with fish meal-based diets containing either 0% (control), 2% or 5% citric acid on a dry basis. Feces were collected by settling and by stripping. Apparent availabilities of calcium and phosphorus were greatly affected by citric acid supplementation in rainbow trout but not in goldfish. Phosphorus levels in feces of fish fed a diet with 5% citric acid were approximately half of that of fish fed the control diet (0% citric acid) in the rainbow trout trial. This pattern was consistent during the 5-week feeding trial. A dietary supplement of citric acid as high as 5% did not reduce feed intake or appetite of rainbow trout. Conversely, this level of dietary acidification led to a marked reduction of feed intake in goldfish. Dietary supplementation of citric acid at 2% level did not reduce feed intake of goldfish; however, this level of dietary acidification had little effect on the apparent availability of major minerals in fish meal-based diet. Levels of non-fecal excretion of calcium and phosphorus, inorganic phosphorus in urine, and citric acid in feces were increased in rainbow trout fed 5% citric acid. The pH values of the feces and urine were decreased in rainbow trout fed citric acid. Plasma bicarbonate, plasma calcium and phosphorus, and blood pH of rainbow trout tended to increase by a 5% dietary supplementation of citric acid. The soluble inorganic phosphorus content increased in the diets and decreased in the feces of rainbow trout by supplementing the diet with 5% citric acid. Feces samples of rainbow trout collected by stripping provided similar availability values to data collected by settling for most elements except sodium, which had negative values in all dietary treatments.

Chemical composition and protein digestibility of poultry by-product meals for salmonid diets

Abstract Poultry by-product meal (PBM) is a potential substitute for a portion of the fish meal typically used in salmonid feeds. The nutritional value of commercial PBM as a fish meal replacement will depend primarily upon the quality and quantity of protein in a particular PBM batch. The purposes of this study were to quantitate the chemical variability in samples of PBM obtained from several manufacturers in North America, and to determine the digestibility of PBM protein by salmonids using one in vivo and three in vitro methods. The range in dry weight proximate composition among PBM samples was 55–74% for protein, 10–19% for lipid, and 11–23% for ash. Of the three in vitro methods for predicting in vivo protein digestibility, a method using trout pyloric ceca enzymes was the most sensitive and was more closely correlated to in vivo results than the other in vitro methods examined. We found significant differences in chemical composition and protein digestibility of PBM samples obtained from different manufacturers, illustrating the range of protein quality in PBM products that fish feed manufacturers will encounter in the marketplace.

Effects of heat treatment and substitution level on palatability and nutritional value of soy defatted flour in feeds for Coho Salmon, Oncorhynchus kisutch

An in vivo digestibility trial and a feeding trial were conducted to determine the extent to which heat treatment, nutritional quality, and palatability of hexane-extracted, defatted soy flour (SF) influenced growth of fingerling coho salmon. Heat treatment of SF (autoclave, 1.7 atm, 121°C) lowered trypsin units inhibited (TUI) from 181 to 1.8 after 20 min and lowered protein solubility from 98% to 70%. Longer heating periods further reduced SF protein solubility, but did not substantially reduce TUI. The apparent digestibility coefficient (ADC) of protein from heated SF (90.8) was significantly higher than the ADC of unheated SF (74.3), but significantly lower than the ADC of the wheat gluten basal diet (98.2). In the feeding trial, fish weight gain was reduced in a step-wise fashion at each level (15, 20, or 25%) of unheated SF inclusion in the diet. Fish fed diets containing heat-treated SF gained more weight at each SF inclusion level compared to their corresponding unheated treatment groups, but inclusion of heat-treated SF greater than 15% substitution of herring meal protein resulted in reduced weight gain compared to fish fed the control diet. Krill supplementation (5%, combination of dried and frozen) increased weight gain in fish fed diets containing 25% heated or unheated SF, primarily by restoring feed intake. In fish fed the heated 25% SF diet with krill, feed intake and average weight gains were equivalent to control diet levels. Fish fed the unheated SF diet with added krill had higher feed intake and weight gains than fish fed the equivalent diet without added krill, but gains were significantly lower than controls. Calculated indices of fish performance, e.g., specific growth rates, feed conversion ratios, protein retention ratios, and apparent net protein utilization (percentage protein retention) displayed patterns similar to weight gain results. In this study, a 20 min heat treatment of SF reduced trypsin inhibitor activity to physiologically insignificant levels, increased protein digestibility, and also allowed a successful 15% substitution of SF for herring meal protein. It appears that reduced feed intake associated with unheated SF was responsible for approximately one-half of the observed reduction in weight gain. Lower nutritional value of the unheated or insufficiently heated SF was responsible for the remaining reduction in fish performance. Therefore, a combination of proper heat treatment and supplementation with palatability-enhancing feed ingredients can overcome these problems, even in young Pacific salmon which are known to be extremely sensitive to soybean meal in their feeds.

Color and flavor analyses of fillets from farm-raised rainbow trout (Oncorhynchus mykiss) fed low-phosphorus feeds containing corn or wheat gluten

Abstract Rainbow trout were fed one of three diets for 12 weeks: a low phosphorus diet containing corn gluten, a low phosphorus diet containing wheat gluten, or a commercial control diet. Fillets were analyzed by a colorimeter and by sensory preference tests. Raw fillets from fish fed the corn gluten-based diet had the highest b* values (yellow color) and received significantly lower visual acceptance scores than fillets from the other dietary treatments. Dietary supplementation with 100 μg/g canthaxanthin increased the a* values (red color) and improved visual preference scores of raw fillets from the corn-gluten fed fish. Incorporation of either corn gluten or wheat gluten into the diet did not adversely affect flavor of the fillets.

Estimation of protein digestibility—IV. Digestive proteinases from the pyloric caeca of coho salmon (Oncorhynchus kisutch) fed diets containing soybean meal

The goal of this study was to better understand why dietary soybean products are poorly utilized by salmonids. The influence of dietary intake on coho salmon fingerling weight gain and specific properties of pyloric caeca enzymes was investigated. Fingerlings were fed diets containing heated or unheated soybean meal (SBM) or Promoveal™, as 15–25% herring meal replacer, for 8–12 weeks. Fish fed to apparent satiation with diets containing heated SBM replacer gained more weight than those fed unheated SBM at the same level. Fish increased in body weight at the same rate when fed restricted rations containing either 15% SBM replacer that was variously heated up to 20 min, 15% Promoveal™ replacer or the herring meal basal diet. After the experimental diets were fed, digestive proteinases were isolated from the pyloric caeca. Yield of pyloric caeca enzymes (PCE), recovery of trypsin in PCE, soybean trypsin inhibitor (SBTI) sensitivity of PCE trypsin, specific activity of PCE trypsin and in vitro casein digestibility by PCE were determined for each dietary group. Weight gain vs in vitro casein digestibility by PCE was linear for animals fed unheated SBM to apparent satiation (r2 = 0.71, P < 0.1) but not for animals fed either heated SBM to apparent satiation or variously heated SBM as 15% replacer at restricted levels. Trypsin from fish fed diets with heated or unheated SBM, but not Promoveal™ replacer, was less sensitive to SBTI than fish fed no SBM. For fish fed diets with variously heated SBM as 15% replacer, the SBTI activity of the SBM and SBTI inhibition of PCE trypsin were inversely related (r2 = 0.88, P < 0.05). The yield of PCE was higher for fish fed 25% of heated SBM replacer than it was for diet groups fed less SBM. The yield of PCE trypsin was higher from animals fed 25% heated SBM replacer than those fed diets with a lower percentage of heated SBM replacer. Feeding coho fingerlings rations with SBM replacer appears to promote physiological compensation of PCE. Heat stable and/or heat-activated factor(s) and SBTI appear to cause the compensation of salmon digestive proteinases from coho salmon fed diets with SBM.

Gastric abnormalities in rainbow trout (Oncorhynchus mykiss) fed amine-supplemented diets or chicken gizzard-erosion-positive fish meal

Abstract Fish meals produced from fish containing high levels of histamine can be acutely toxic to chickens, causing gizzard erosion (GE), black vomit disease, and death after 3–5 days of feeding. Fish meals are sometimes selected for aquaculture use on the basis of chicken toxicity testing, although little scientific evidence exists to support this practice. In this study, growth, feed intake, and development of gastric abnormalities were assessed in juvenile rainbow trout fed diets containing fish meal acutely toxic to chickens, or fed casein or fish meal diets supplemented with histamine and two suspected potentiators of histamine toxicity, putrescine and cadaverine, and abusively heated. No signs of acute toxicity or mortality occurred in the groups of fish during the course of the 16-week study. Fish fed diets containing GE-positive fish meal had distended stomachs, but no gastric lesions or cellular abnormalities. Similar effects were obtained by feeding diets containing casein or GE-negative fish meal supplemented with histamine (2000 mg/kg dry diet). The addition of putrescine and cadaverine (500 mg/kg dry diet each) to the histamine-supplemented diets had no further effect. Feed consumption, feed efficiency, and growth were similar among dietary treatments, indicating that stomach distention did not reduce feed intake or impair gastric function. This study showed that rainbow trout are less sensitive than chickens to GE-positive fish meal and that there is no correlation between positive GE score and the nutritional value of the fish meal for rainbow trout. This study also showed that stomach distention resulting from feeding diets containing GE-positive fish meal could be duplicated by feeding diets supplemented with 2000 mg histamine/kg diet.