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    • Article

      Dietary requirements of rainbow trout for tryptophan, lysine and arginine determined by growth and biochemical measurements 

      MJ Walton, CB Cowey, RM Coloso & JW Adron - Fish Physiology and Biochemistry, 1986 - Springer Verlag
      Three separate studies were performed to determine the dietary requirements of rainbow troutSalmo gairdneri for tryptophan (Trp), lysine (Lys) and arginine (Arg) from both growth and biochemical data. The growth studies were carried out over a 12 week period. From graphical plots of % mean weight gain against % amino acid in diet the following requirement values were obtained, Trp 0.25% diet (0.4% dietary crude protein); Lys 1.9% diet (4.3% dietary protein); and Arg 1.6–1.8% diet (3.6–4% dietary protein). Plasma and liver amino acid concentrations measured 20h after feeding did not prove useful for determination of requirement values. Hepatic activities of Trp pyrrolase (TP), Lys α ketoglutarate reductase (LKGR) and arginase were not significantly affected by varying levels of Trp, Lys and Arg respectively in the diet. TP has a cytosolic location and a Km of 0.2 mM for Trp; LKGR is mitochondrial and the Km for Lys is 7.3 mM; arginase is also mitochondrial and has a Km of 4.9 mM for arginine. Measurements of expired14CO2, after injection of a tracer dose of14C amino acid, did allow estimates of requirement levels to be made. The values obtained from the oxidation studies reinforced the values obtained from the growth data but were not precise enough to justify using this method on its own.
    • Article

      The effects of dietary tryptophan levels on growth and metabolism of rainbow trout (Salmo gairdneri) 

      MJ Walton, RM Coloso, CB Cowey, JW Adron & D Knox - British Journal of Nutrition, 1984 - Cambridge University Press
      1. Groups of rainbow trout (Salmo gairdneri) (mean weight 14 g) were given diets containing 0.8, 1.3, 2, 3, 4 or 6 g tryptophan/kg diet for 12 weeks.

      2. By analysis of the growth results, the dietary requirement of tryptophan was found to be 2.5 g/kg diet (equivalent to 50 mg/kg biomass per d).

      3. Carbon dioxide expired by trout following intraperitoneal injection of [14COOH]tryptophan contained little radioactivity when dietary tryptophan level was low but, above 2.0 g/kg diet, it increased rapidly with increasing dietary tryptophan level. The break point in the dose-response curve did not, however, coincide with that from the growth results.

      4. Changes in concentrations of free tryptophan in blood and liver and activity of hepatic tryptophan pyrrolase (EC 1.13.11.11) in response to changes in dietary tryptophan concentration did not provide reliable indicators for quantifying dietary requirement. Unlike the situation in mammals, blood tryptophan was not protein-bound to any appreciable extent. Tryptophan pyrrolase of trout has properties which suggest it has no apoenzyme form.

      5. In fish given adequate levels of tryptophan injected intraperitoneally with a tracer dose of [14COOH]tryptophan, 60% of the dose was incorporated into body protein within 1 d. The turnover of the label in this protein is very slow.

      6. Those trout given diets deficient in tryptophan suffered from severe scoliosis and lordosis as well as having increased liver and kidney levels of calcium, magnesium, sodium and potassium.