Effect of soybean protein on serological response, non-specific defense mechanisms, growth, and protein utilization in rainbow trout.

Rainbow trout (Oncorhynchus mykiss) were fed chemically and immunologically defined diets containing either a low-temperature fish meal or soybean preparations containing high (SBM) or low levels of the globular antigenic proteins glycinin (G) and beta-conglycinin (BC) for 26 weeks. While trout fed both soybean preparations exhibited poorer growth than those fed fish meal, those fed the soya diet with high levels of G and BC showed the most significant growth diminution, elevated feed conversion and impaired utilization of dietary protein. Changes in intestinal morphology were also observed in fish fed the SBM diet, coinciding with the inferior nutritional performance. Several serologic and non-specific immune defense mechanisms were monitored. Cell counts showed increased leukocyte cell numbers as well as increased concentrations of plasma protein and immunoglobulin in the soya-fed fish. Increased neutrophil, monocyte and macrophage activity, as assessed by several oxidative radical production and phagocytic index assays, were higher in the soya-fed fish, possibly indicating an inflammatory or hypersensitivity response. The results of this study suggest that antigenic soya protein affects non-specific defense mechanisms, growth performance, and protein utilization in rainbow trout. Furthermore, it would appear that dietary sensitivity can be overcome by process removal of this immunologically characterized antigen in soybean protein. Serological and immunological assessments appear to be very useful criteria for evaluating various protein sources for fishes.

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.

Interactions among dietary minerals, arginine and lysine in rainbow trout (Salmo gairdneri).

Studies were conducted to determine whether interactions occur among dietary lysine, arginine and monovalent minerals in rainbow trout. In one experiment, rainbow trout fingerlings were fed diets containing three levels of lysine (2.4, 3.1 and 3.8 g per 100 g diet), two levels of arginine (1.7 and 2.5 g per 100 g diet) and two mixtures of Na(+) K(+) and Cl in a 3×2×2 factorial design. The mixtures varied in the proportions of cations to anions such that Cl equalled the sum of Na(+) and K(+) (cations - anions = 0 mEq/kg diet) in one mixture and exceeded the sum of Na(+) and K(+) (cations - anions = -200 mEq/kg diet) in the second mixture. Growth and efficiency of feed conversion were not affected by dietary lysine and arginine in fish fed diets containing - 200 mEq/kg balance, but when fish were fed diets containing a 0 mEq/kg balance, 3.8% lysine and a combination of 3.1% lysine and 2.5% arginine depressed both measures of response. Trout receiving the 0 mEq/kg cation-anion balance had significantly higher free histidine concentrations and lower free lysine concentrations in muscle and higher hepatic arginase activity (P≤0.01) than those receiving -200 mEq/kg. In another experiment, trout were fed diets containing three levels of K(+) (21, 191 and 360 mEq/kg), two levels of Na(+) (21 and 191 mEq/kg) and two levels of Cl(-) (179 and 347 mEq/kg) in a 3×2×2 factorial design. Growth and efficiency of feed conversion were depressed and hepatosomatic index increased with higher levels of dietary K(+) (P≤0.01), Na(+) (P≤0.05) and Cl (P≤0.01), with significant K(+) x Cl(+) (P≤0.01) and K(+) x Na(+) x Cl (P≤0.05) interactions. Increasing dietary K(+) resulted in increased levels of muscle free histidine and decreased levels of muscle free lysine and arginine (P≤0.01), while increasing dietary Cl increased muscle free lysine, the effect of which was dependent on dietary potassium (K(+) x Cl(-), P≤0.01). It is concluded that dietary levels of K(+), Na(+) and Cl(-), irrespective of overall cation-anion balance of these minerals, affects growth rate, efficiency of feed utilization and the metabolism of basic amino acids in tissues of trout. Excess lysine causes depressed growth and efficiency of feed utilization. These effects were due to a lysine toxicity rather than a lysine-arginine antagonism, as they were not prevented by supplemental dietary arginine.

Urea cycle activity and arginine formation in rainbow trout (Salmo gairdneri)

Studies were conducted to determine whether rainbow trout fingerlings possess the ability to synthesize arginine via the urea cycle. Several urea cycle enzymes were detected in trout tissues. An experiment was conducted to determine whether the enzymes increase in response to starvation or in response to dietary protein level (0, 30, 40, 50% protein). Although some effects were observed, they did not appear to be consistent with the function of the urea cycle as a mechanism of detoxifying ammonia in the fish. The activities of kidney arginase and liver and muscle carbamoyl phosphate synthetase (CPS) were higher (P less than 0.05) when protein was omitted from the diet (P less than 0.05) than when it was present but were unaffected by protein level otherwise. The activities of liver arginase and kidney and muscle CPS and ornithine transcarbamoylase (OTC) were higher (P less than 0.05) in starved fish than in fish that received adequate levels of protein. Liver CPS and OTC were lower in starved fish than in fish fed 30% protein. L-[l-14C]ornithine hydrochloride and L-[carbamoyl-14C]citrulline, injected intraperitoneally, were incorporated into tissue arginine, a finding consistent with arginine biosynthesis via the urea cycle. When one-half of dietary arginine was replaced by equimolar amounts of glutamic acid, ornithine or citrulline, glutamic acid markedly reduced growth (P less than 0.05), whereas growth was depressed only slightly by ornithine (P less than 0.05) and not depressed by citrulline (P greater than 0.05). We conclude that trout have a urea cycle that provides for potential arginine biosynthesis.

Factors affecting dietary requirement and deficiency signs of L-tryptophan in rainbow trout.

Two experiments were conducted to determine the concentration of dietary tryptophan needed for optimal growth and survival of fingerling rainbow trout (Salmo gairdneri), to characterize signs of tryptophan deficiency, and to ascertain the effects of niacin on deficiency signs. Test diets containing either hydrolyzed or intact casein were fed with graded levels of added L-tryptophan (0.0, 0.25, 0.50, 0.75 and 1.0 g/100 g protein). Maximum growth occurred at 0.75 and 0.50 g tryptophan in fish fed hydrolyzed and intact casein, respectively. Changes in mineral and amino acid mixtures in the intact casein diet yielded a cation-anion (Na + K - Cl) balance of +15.3 meq/100 g diet and pH of 6.44, compared with a balance of -21.3 and -25 meq, and pH 5.8 and 4.4 for unmodified hydrolyzed and intact casein diets, respectively. Analysis of growth by the polynomial regression function; Y = 0.16 + 0.429X - 0.26X2, where Y = mean daily gain in grams, and X = grams of added tryptophan/100 g protein, predicted that at least 0.58 g of tryptophan was needed for maximum weight gain. Analysis of apparent pathology-free fish by the function; Y = 34.33 + 147.33X -83.87X2, where Y = percentage with no signs of deficiency, and X = grams of added tryptophan, predicted that 0.63 g tryptophan/100 g protein was needed for optimum health scores. Deletion of supplemental niacin did not affect fish response to tryptophan.

Branched-chain amino acid aminotransferase activity in the tissues of lake trout.

The enzyme branched-chain amino acid aminotransferase (BCAT) was found in five tissues of fingerling lake trout, Salvelinus namaycush, (listed in order of decreasing tissue specific activity): posterior kidney, skeletal muscle, gill, liver, and anterior kidney. This pattern is consistent with that found in other animals. The results of this study seem to indicate that BCAT in the liver of lake trout has a higher specific activity than that of the rat and that the specific activity is higher in both the liver and skeletal muscle than it is in these organs of the chick.

Differentiation of soluble proteins in cataracts caused by deficiencies of methionine, riboflavin or zinc in diets fed to Atlantic salmon, Salmo salar, rainbow trout, Salmo gairdneri, and lake trout, Salvelinus namaycush.

Water soluble extracts from cataractous and normal salmonid lenses were subjected to thin-layer isoelectric focusing. The cataracts resulted from deficiencies of specific nutrients in diets fed to three species of salmonids as follows: (1) rainbow trout (Salmo gairdneri) fed a diet deficient in riboflavin; (2) Atlantic salmon (Salmo salar) fed a diet deficient in methionine; and (3) rainbow trout and lake trout (Salvelinus namaycush) fed a diet deficient in zinc. In all tests, the protein pattern of cataractous lenses differed from that of normal lenses. Each cataract caused by the different dietary deficiencies had a specific pattern of soluble lens proteins. Even though the general patterns of the soluble lens proteins for all three salmonids though the general patterns of the soluble lens proteins for all three salmonids studied were similar, a specific pattern was unique for each of the species.

Biomicroscopic and histologic pathology of the eye in riboflavin deficient rainbow trout (Salmogairdneri).

Quadruplicate lots of 35 fingerling rainbow trout (mean body weight 11.2 g) were fed for 20 weeks a complete diet or one deficient in riboflavin. Five fish from each low were examined for ocular lesions each week. At the end of the experiment eyes of three fish form each lot were examined histologically. Beginning with the 14th week, epithelial changes were present in the cornea; they appeared as thickening of the stroma and endothelium and resulted in clouding. Opacity of the lens originated in the posterior subcapsular cortex and progressed to lens fiber autolysis and liquefaction.

Heat increment associated with dietary protein, fat, carbohydrate and complete diets in salmonids: comparative energetic efficiency.

The heat increment (HI) of feeding, which is the increased heat production following consumption of food by an animal, accounts for as much as 30% of the ingested metabolizable energy (ME) in mammals and birds. The purpose of these experiments was to measure the HI associated with the feeding of a complete diet and purified fat, protein, and carbohydrate to salmonids. Measured amounts were fed and the heat production was measured by direct calorimetry. Increased heat production was observed about 30 minutes after feeding and remained elevated for 1 to 5 hours, depending on the amount and type of material fed. The HI of protein was much lower with fish than with mammals and amounted to less than 5% of the ingested ME. The HI's of carbohydrate and protein were not significantly different from each other but both were higher than fat. The HI, when complete diets were fed, was less than 3% of the ME. The net energy of protein is higher for fish than for birds or mammals. A major part of the superior energetic efficiency of fish is due to the low energy cost of protein metabolism.

The effect of supplemental dietary amino acids, minerals and vitamins on salmonids fed cataractogenic diets.

Three nutritional experiments were conducted to determine the effects of various nutrients on the development of ocular lesions in brook trout, Salvelinus fontinalis, lake trout, Salvelinus namaycush, and rainbow trout, Salmo gairdneri. Supplemental methionine prevented development of cataracts and stimulated growth in trout fed diets containing soy protein isolate as the sole protein. Supplemental riboflavin prevented high mortality, cataracts, and other lens-corneal lesions shown in trout fed a semipurified diet containing casein and gelatin. Swim-up fry which were fed a vitamin A-deficient semipurified diet from first feeding grew slowly, developed edema, corneal lesions, and retinal degeneration, but not lens cataracts. In contrast, feeding the same vitamin A-deficient diet to older trout previously fed vitamin A did not cause ocular lesions or other signs of deficiency. Supplemental beta-carotene prevented ocular lesions in swim-up trout held in warm (12.4 degrees C), but not in cold (9 degrees C) water.

Effects of PCBs, DDT, and mercury compounds upon egg production, hatchability and shell quality in chickens and Japanese quail.

Dietary polychlorinated biphenyls (PCBs), DDT and related compounds, in well controlled experiments, produced no detrimental effects upon egg shell quality in Single Comb White Leghorm chickens or in Japanese quail. PCBs caused some decrease in egg production and a drastic reduction in hatchability in chickens, but not in Japanese quail. Inorganic mercury as HgSO4 or HgCl2, at dietary levels up to 200 p.p.m. of Hg, had only small effects, if any, upon egg production, hatchability, shell quality, morbidity and mortality. However, methyl mercury chloride at levels which provided 10 or 20 mg. of Hg per kg. of diet caused severe effects upon egg weight, egg production, fertility, hatchability, egg shell strength, morbidity and mortality. The results of these experiments demonstrate that the decrease in egg shell quality which has occurred in eggs of White Leghorn hens over the past three decades is not due to contamination of commercial feeds with DDT or its derivatives, or with PCBs. The extent to which environmental contamination with methyl mercury is responsible for decreased egg shell strength in commercial laying hens, and possible synergistic relationships between methyl mercury, DDT, DDE and PCBs in reducing egg production, hatchability and shell strength, remain to be determined.