Finn Utne

The effect of ascorbic acid supplementation in broodstock feed on reproduction of rainbow trout (Salmo gairdneri)

Abstract Two experimental diets differing in supplementation of ascorbic acid and a third commercial diet were fed to rainbow trout broodstock. A supplementation level of 115 mg ascorbic acid per kg significantly increased the number of hatching eggs compared to eggs from fish without dietary ascorbic acid supplementation. Fish reared on the commercial diet gave eggs of similar quality as from the ascorbic acid supplemented experimental feed. The results indicate that ascorbic acid is essential for reproduction in rainbow trout. Broodstock fish should be fed adequate amounts of the vitamin to provide eggs with more than 20 μg ascorbic acid/g.

Effect of different acidified wet feeds on protease activities in the digestive tract and on growth rate of rainbow trout (Salmo gairdneri Richardson)

Abstract Acidified feeds treated with hydrochloric, formic or sulphuric acid were fed to rainbow trout ( Salmo gairdneri Richardson) to test the effects on protease activities, growth and feed utilization. The acidified feeds were prepared by mixing a frozen stored control feed with fish silage made from the same feed acidified with 2.5% ( w/w ) of hydrochloric acid, formic acid or sulphuric acid, respectively. To the silages was added 0.5% ( w/w ) propionic acid as a fungicide. The experimental feeds contained 0, 40, 60 and 100% of the fish silages to give final concentrations of, respectively, 0, 1.0, 1.5 and 2.5% ( w/w ) of each acid tested. Hydrochloric acid had no apparent effect on growth or proteolytic activities in any part of the digestive tract. Formic acid at all levels tested seems to have a depressive effect on both growth and proteolytic activities. Sulphuric acid showed similar effects, with the exception that the protease activity in the stomach was not depressed. Acidified feeds showed lower feed utilizations than the control feed, this being most pronounced for the formic acid silage.

Antioxidant properties of methionine esters.

DURING feeding experiments we have found that 0.5 percent methionine in a semisynthetic diet containing 12 per cent cod liver oil prevents yellow discoloration of the diet and also the destruction of vitamins A and E (refs. 1–3). We have also studied the antioxidant properties of methionine and some derivatives using simple manometric techniques4 and have recorded the near infrared spectrum of CCl4 extracts of the semisynthetic diet. The spectrophotometric data showed a relatively constant peak at 2.34µ and a variable peak at 2.88µ which increased as oxidation progressed, permitting use of the ratio of absorptions at these two wavelengths as an additional measure of oxidation. Using both criteria hydrochlorides of the methyl and ethyl esters of methionine showed unique properties. In contrast to other compounds which were tested there were rapid but relatively small initial changes followed by extended periods in which only very slow changes took place. The esters therefore seemed to be transformed to antioxidant compounds acting in a similar way to butylated hydroxy toluene (BHT).