No abstract

This study measured the dietary selenium requirement of rainbow trout and their response to excessive levels of dietary selenium. A dietary selenium level of 0.07 microgram/g dry feed with a waterborne selenium level of 0.4 +/- 0.2 microgram/liter and a dietary vitamin E level of 0.4 IU/g dry diet was sufficient to prevent frank selenium deficiency symptoms. Maximal plasma GSH.px activity was obtained at a dietary selenium level between 0.15 and 0.38 microgram/g dry feed which is less than the average selenium concentration of commercial diets. Chronic dietary selenium toxicity occurred at 13 microgram selenium/g dry feed. Major effects of selenium toxicity were reduced growth rate, poor feed efficiency and a high number of mortalities. No histopathological lesions or significant deviation in the investigated blood parameters or liver somatic index were detected in trout raised on diets containing 13 microgram selenium/g dry feed. Tissue selenium analysis indicated that trout can maintain homeostasis with dietary selenium levels up to 1.25 microgram/g dry feed. The selenium uptake and accumulation in tissues of trout reared on diets containing in excess of 3 microgram/g dry feed may ultimately be toxic to trout if maintained over long periods of time.

No abstract

Relative performances of dietary acid-insoluble ash, celite (a source of acid-insoluble ash), and chromic oxide as digestibility references were compared. Apparent digestibilities of dry matter, crude protein, and gross energy in a practical diet fed to rainbow trout (Salmo gairdneri) were similar regardless of indicator used. Acid-insoluble ash can bean effective indicator for digestibility trials with fish. Its natural occurrence in fish foods and feedstuffs and ease of analysis make it preferable to added indicators, such as chromic oxide, in many circumstances. When the acid-insoluble ash content of a diet is low, the addition of celite can improve the precision of the analysis without affecting absolute values of digestibility coefficients.

inary studies were designed to test two basic assumptions: 1) that the M.E. value of an ingredient is independent of the other diet components, and 2) that the value remains relatively constant irrespective of the age of type of bird to which