Press cake meals were prepared from previously frozen herring immediately following thawing and after storage for 8 or 12 days at 2-5°C. Each of the raw sources of hemng was subjected to two processing temperatures, 75°C and 1OO"C, during meal preparation. Also, protein hydrolysates were prepared using ocean perch when fresh or after storage at 2-5°C for 4 or 8 days. Subsequently, each of the three hydrolysates was dried at 85°C or 93°C.In two separate experiments, each of the hemng press cake meals and dried perch protein hydrolysates was blended with a reference diet in a 30:70 ratio (test protein source: reference diet).All diets contained 5 g kg-' chromic oxide as an indigestible marker. The reference diet and all test diets were provided to satiation to chinook salmon in salt water and rainbow trout in fresh water, with digestibility of organic matter, protein and energy measured by difference. Digestibility of protein was also measured by the pH-stat and dilute pepsin solubility in vitro techniques.The results indicated that variation in processing temperature to a maximum of 100°C had little effect on digestibility of marine fish protein sources. By contrast, raw material storage for 8 days or more at 2-5°C prior to processing was found to reduce organic matter digestibility and sometimes nitrogen digestibility in salmonids. In vitro measures of digestibility were of little help in predicting the nutritive value of the test protein sources. Cadaverine level in herring press cake meal was shown to be a good indicator of spoilage in the raw material.

Free erucic acid (EA) (C22:1) was blended with Cambra oil (CBO), sunflower oil (SFO), and animal lard (AL) at 45% (w/w). Six experimental diets were formulated to incorporate either CBO, SFO, AL, or EA blended oils (CBO plus EA, SFO plus EA), or fats (AL plus EA) at 8%. The adverse effects of dietary EA blended with various types of oils or fats were studied by feeding 180-day-old White Leghorn cockerels for a 4-week growing period. In general, adverse effects of dietary EA were clearly reflected in feed consumption, chick growth, and apparent digestibility of total lipids as well as individual fatty acids. The AL plus EA produced significantly greater adverse effects than with SFO plus EA. The diet containing CBO (low EA, 5.1% rapeseed oil) depressed chick growth and feed consumption, but no additive effect was manifested when EA was supplemented. The fatty acid profile of dietary SFO appears to counteract the metabolic burden of excess dietary EA. It was concluded that high linoleic acid content in SFO may be the major contributing factor in alleviating the adverse response to EA.

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