to acidic substances, such as aspartic acid and glutamic acid. The pattern is reasonable considering the chemical characteristics of the feed items the fish would seek in the natural environment (Mackie, 1982; Adams and Johnsen, 1986a).

The presence of certain compounds can also act as feeding deterrents. This phenomenon has been shown to occur with certain combinations of amino acids (Adron and Mackie, 1978; Mackie and Adron, 1978; Mackie, 1982). Trimethylamine or its oxidation products, which are produced in decaying fish flesh, were shown to cause a decrease in feed consumption in turbot (Mackie and Adron, 1978), plaice (Mackie, 1982), and chinook salmon (Hughes, 1991) when these compounds were added to the diet. Salmonids (Hung and Slinger, 1980; Ketola et al., 1989) and yellowtail (Murai et al., 1988) show aversion to highly oxidized oils and fishmeals.