Evaluation of Acid-Insoluble Ash as an Indicator of Feed Digestibility in Rainbow Trout (Salmo gairdneri)

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.