DIGESTIBILITY OF VARIOUS FEEDSTUFFS BY POST-JUVENILE CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) IN SEA-WATER .2. MEASUREMENT OF DIGESTIBILITY

This study was undertaken to determine the digestibility of organic matter, crude protein, and gross energy, in selected animal and plant feedstuffs using post-juvenile chinook salmon held in running 8-12.5-degrees-C filtered sea water (28-31 ppt) on a natural photoperiod. Feces were collected by either a modified Guelph procedure, stripping or intestinal dissection using chromic oxide as the indigestible marker. Most fishmeal sources contained more digestible energy for chinook salmon than did the other test animal and plant protein sources. Two sources of poultry by-product meal differed markedly in percentages of digestible protein and energy. Blood meal, which was dried in a continuous dryer, had very low percentages of available protein and energy. A commercial source of canola meal, one source of glucosinolate-free canola meal and rapeseed protein concentrate were all well digested. The digestibility of commercial sources of soybean meal and soybean protein isolate could not be ascertained accurately because fish fed test diets containing these protein sources exhibited poor appetite. The energy in extruded wheat was absorbed much better than that in wheat middlings. The Guelph system of fecal collection appeared to provide reliable estimates of feedstuff digestibility using chinook salmon in sea water.