Carol MacMILLAN

Intestinal absorption of astaxanthin, plasma astaxanthin concentration, body weight, and metabolic rate as determinants of flesh pigmentation in salmonid fish

Abstract Experiments were conducted to determine whether poor intestinal absorption of astaxanthin or some other metabolic factor is primarily responsible for pigmentation failure in white chinook salmon and small juvenile fish of other salmonid species. None of the fish studied failed to absorb astaxanthin from a single oral dose of the pigment. Intensity of flesh pigmentation in coho ranging in weight from 30–400 g, and fed a diet supplemented with astaxanthin, was significantly correlated with body weight. There was no correlation, however, between flesh colour and plasma astaxanthin concentration or between body weight and plasma astaxanthin concentration. Dietary triiodothyronine reduced both flesh pigmentation and plasma astaxanthin. It is concluded that poor flesh pigmentation results from rapid metabolism of absorbed pigment to colourless derivatives rather than from failure of the fish to absorb pigment.

Muscle Pigmentation and Plasma Concentrations of Astaxanthin in Rainbow Trout, Chinook Salmon, and Atlantic Salmon in Response to Different Dietary Levels of Astaxanthin

Abstract Pigmentation development was studied in rainbow trout Oncorhynchus mykiss, chinook salmon O. tshawvytscha, and Atlantic salmon Salmo salar fed similar practical diets supplemented with 40, 70, or 100 mg astaxanthin/kg of diet. The initial mean body weights of the respective species were 158, 198, and 191 g. The rainbow trout were reared in freshwater at 6.0–11.3°C, the chinook salmon in seawater at 8.8–14.4°C, and the Atlantic salmon in seawater at 7.1–12.7°C. The response of flesh pigmentation to dietary pigment was most rapid in rainbow trout and slowest in Atlantic salmon. Chinook salmon showed the greatest variation in response to the different dietary concentrations of astaxanthin, followed by rainbow trout and Atlantic salmon. In both rainbow trout and Atlantic salmon, pigmentation was most intense in the distal section and decreased anteriorly. In chinook salmon, pigmentation was most intense in the midsection, followed by the anterior section and then the distal section. Postprandial plas...

Techniques for evaluation of dietary protein quality for the rainbow trout (Salmo gairdneri)

Abstract Selection of the test fish for uniformity of body weight allowed bioassays for protein quality to be conducted within a 3-week period with small numbers of fish. Slope-ratios from the linear responses of body weight gain to graded levels of protein intake gave practical comparisons of the quality of protein sources. The use of different dietary concentrations of protein sources under test may indicate responses to factors other than those associated with protein per se. The slope-ratio technique lends itself to simultaneous estimations of the relative efficiency of protein energy utilization, which are important in evaluation of plant protein concentrates.