Gary L. Rumsey

Dietary intake of immunostimulants by rainbow trout affects non-specific immunity and protection against furunculosis.

Immunostimulant preparations Macrogard, Candida utilis, Saccharomyces cerevisiae, Evetsel, Chitosan, or FinnStim were mixed into semipurified diets and fed to groups of rainbow trout for 1 week. Fish were bled by non-lethal caudal puncture and blood samples assayed for changes in non-specific cellular immunity and humoral protein levels. In the immunostimulated fish, hematocrit levels and lymphocyte counts remained relatively stable; however, elevations were observed in oxidative radical release, myeloperoxidase activity, phagocytic indexes, and potential killing activities of phagocytic cells including neutrophils. Total plasma protein and total immunoglobulin levels were elevated by the dietary immunostimulants. A challenge with the virulent pathogen that causes furunculosis, Aeromonas salmonicida, showed that the immunostimulated groups of fish were more resistant to the disease, confirming the potential use of these substances in fish culture for the prevention of disease.

Growth, carcasss composition, and taste of rainbow trout of different strains fed diets containing primarily plant or animal protein

Abstract Ten rainbow trout (Salmo gairdneri) strains were evaluated during early growth from 30 g to 250 g on two diets — one based on plant protein (soybean and cottonseed meal) and the other on animal protein (fish meal). Diets were formulated to be nutritionally isocaloric and isonitrogenous. Fish were fed identical starter diets until they weighed 30 g. Significant differences in growth rate were found attributable to fish strain. Differences associated with diet were nonsignificant. Percent dress-out data based on eviscerated weight, deboned weight, and fillet weight also showed significant differences in yield attributable to fish strain, but not to diet. Carcass composition varied among strains, but none of the differences could be attributed to diet. Organoleptic tests showed no differences in flesh acceptability associated with either fish strain or diet, and all trout tested were equally acceptable to human taste panels.

Nutritional value of dietary nucleic acids and purine bases to rainbow trout (Oncorhynchus mykiss)

Rainbow trout were fed diets with graded levels (0.6%, 1.6%, 2.5%, and 4.1%) of a yeast nucleic acid extract corresponding to dietary Saccharomyces cerevisiae levels of 7.5%, 20%, 30% and 50% or diets supplemented isonitrogenously (0.8% N) with free purines (adenine, guanine, xanthine, and hypoxanthine) in two 12-week studies. Fish fed increasing levels of yeast extract manifested significant (P < 0.05) corresponding incremental increases in growth and nitrogen retention. No negative effects on feed intake were observed. When fish were fed supplemental free purines, adenine was shown to be a potent inhibitor of feed intake and growth. While supplementation with the remaining purines did not negatively affect feed intake or growth, carcass nitrogen retention was significantly depressed, indicating the lack of a nitrogen-sparing effect. Our results indicate that the nutritional significance of free dietary adenine versus nucleic acid-bound adenine in yeast or yeast nucleic acid is an important consideration in evaluating the suitability of single cell proteins in fish feed formulations.

Effect of high dietary concentrations of brewer's dried yeast on growth performance and liver uricase in rainbow trout (Oncorhynchus mykiss)

The potential of using yeast nitrogen in fish feeds to replace proteins from conventional sources is an attractive option to nutritionists, feed manufacturers and fish farmers. Experiments were conducted to determine the effects of high dietary levels of brewers dried yeast, with 20% of its protein represented by nucleic acid nitrogen, on the growth, feed conversion efficiency and uric acid metabolism of rainbow trout (Oncorhynchus mykiss). Growth and liver uricase activities were monitored in trout fed diets containing 0, 25, 50 or 75% yeast. Growth was faster and feed conversion more efficient in fish fed diets consisting of 25% yeast; the diets containing 50 and 75% yeast were seemingly unpalatable to trout. Liver uricase activity, present in all fish, was directly correlated with the dietary level of nucleic acids. It was concluded that although feed intake was depressed at yeast levels greater than 25%, the fish did not appear to be adversely affected physiologically by high dietary levels of nucleic acid nitrogen.

Fish Meal and Alternate Sources of Protein in Fish Feeds Update 1993

Abstract Close to 12% of the worlds 6.5 million metric tons of fish meal is used for aquaculture feeds. If current trends continue, roughly 20% to 25% of total world fish meal production could be used for aquaculture by the year 2000. Fish stocks used in fish meal reduction, however, appear to be in worldwide decline. A growing fish farming industry and a stagnating, if not diminishing, supply of fish meal have sobering economic and technologic implications for fish culture. Unless suitable alternate protein sources are found or other animal feeds begin to rely less on fish meal, fish production costs can be expected to increase dramatically. A precedent was set by the poultry industry, the most economically successful and competitive of the animal agriculture industries. Twenty years ago, the poultry industry consumed up to 80% of fish meal supplies. Through deliberate and well-organized research into alternate protein sources, the industry now uses less than 40% of supplies, and the trend is toward com...

Chemical and nutritional evaluation of soya protein preparations as primary nitrogen sources for rainbow trout (Oncorhynchus mykiss)

Abstract Five soya-bean preparations that had been subjected to various physicochemical processing procedures were chemically defined in respect to proximate analysis, amino acid analyses, protease inhibitor activity, soluble oligosaccharides and antigenicity. These soya preparations were then formulated, along with a low-temperature fish meal control, into six isonitrogenous and isocaloric experimental diets. The diets were fed to rainbow trout ( Oncorhynchus mykiss ) in feeding trials as well as in tests using specially constructed metabolic chambers. Based on the chemical and biological results, we concluded that soya-bean oligosaccharides do not have to be removed or modified for maximum growth or nitrogen utilization by rainbow trout. Likewise, the protease or trypsin inhibitor activity, which was low for all experimental treatments, did not appear to be a major factor in determining fish performance. Although the results regarding naturally occurring soya antigens only suggested allergenicity, it is concluded that more attention should be focused on these heat-stable proteins with antigenic or allergenic potential in fish diets.

Choline-betaine requirements of rainbow trout (Oncorhynchus mykiss)

Abstract A series of experiments with rainbow trout ( Oncorhynchus mykiss ) were conducted to quantify the dietary requirement for choline as well as to determine whether betaine or methionine could spare the trouts choline requirement. Fish weighing 1.4 and 3.2 g, which were acclimated to a choline-deficient semipurified diet for 14 days before the start of the experiments, were shown to have a choline requirement of 813 and 714 ppm, respectively. When an excess of betaine was added to the choline-deficient basal diet, the choline requirement was reduced to about 400 ppm. These results suggest that about half of the trouts choline requirement must be met by choline itself, whereas the other half can be supplied by betaine. However, the requirement for choline itself must first be met before a response to betaine can be obtained. The addition of betaine to a choline-deficient diet resulted in no improvement in weight gain. Likewise, the addition of L-methionine, isomethyl to 1000 ppm choline, was without effect on growth in a basal diet marginally adequate in sulfur amino acids — suggesting that the trouts requirement for choline is not replaceable by methionine. Because the effects of dietary choline on liver lipid were variable and difficult to interpret, it was demonstrated that growth was more sensitive than liver lipid as an indicator of choline status.

Digestibility and energy values of intact, disrupted and extracts from brewer's dried yeast fed to rainbow trout (Oncorhynchus mykiss)

Abstract Although fish meal has historically been used as the primary source of protein in fish feeds, brewers dried yeast (BDY) is presently being investigated as a primary replacement for fish meal. As little is known about the ability of fish to utilize BDY, studies were conducted to study bioavailability of intact BDY as well as several fractions derived from the disrupted yeast to rainbow trout. Dried BDY was fed to rainbow trout and digestibility and energy values were determined. When the yeast cells were fully disrupted, the absorption of nitrogen increased by more than 20% and the metabolizable energy of the yeast by more than 10%. Energy and nitrogen digestibility were further increased after the removal of all wall material and separation of nitrogen into amino acid and nucleic acid fractions. Disruption of the cell wall significantly increased the nutritional value of BDY for salmonid fishes. The findings suggest that further research be conducted on the use and economy of BDY as a primary nitrogen source in fish feeds.

Effect of feeding level and dietary electrolytes on the arginine requirement of rainbow trout (Salmo gairdneri)

Abstract Experiments were conducted to determine the effect of level of feeding (restricted feeding and feeding to satiation) and dietary variations in the balance of monovalent minerals on the arginine requirement of rainbow trout fingerlings. Based on growth and efficiency of feed utilization for growth, the arginine requirement was lower (3.5% of protein) when fish were fed to satiation than when they were fed at a restricted level (4.2% of protein). When calculated on the basis of the amount of arginine consumed per day, however, the requirements were similar for fish subjected to the two methods of feeding. Three balances (acidic, neutral, and alkaline) of sodium, potassium and chloride were used in several experiments. The arginine requirement tended to be higher when fish were fed diets containing the alkaline as compared to the acidic balance of minerals. These studies indicate that the method of feeding has a significant effect on the dietary concentration of arginine needed to maximize growth rate and feed utilization in rainbow trout.

Methionine and Cystine Requirements of Rainbow Trout

Abstract Methionine and cystine requirements of rainbow trout (Salmo gairdneri) were studied by supplementing a 35% protein semipurified basal diet with these amino acids at graded levels in a factorial design. In experiment 1 (initial average weight of fish, 1.5 g), methionirie levels were 0.30, 0.45, and 0.60% of the diet and cystine levels were 0.04, 0.15, 0.30, 0.45, and 0.60%. In experiment 2 (initial average weight of fish, 8.8 g), methionine levels were 0.55, 0.75, and 0.95% and cystine levels were 0.04, 0.08, 0.12, 0.16, 0.24, and 0.32%. Methionine requirement was estimated to be between 0.55 and 0.75% in the presence of adequate dietary cystine and the cystine requirement was about 0.30% with a diet marginally deficient in methionine. The requirement for both sulfur amino acids was, therefore, between 0.85 and 1.05% of the diet or 2.50 and 3.00% of the protein. Molar efficiency of conversion of dietary methionine to cystine was highest (80%) when the diet was deficient in methionine; this efficie...