Betaine, L-alanine, L-glutamic acid, L-arginine, glycine and inosine are known as dietary feeding attractants for many fish species. However, these additives also have very important physiological functions within the animal body. For example, betaine given singly or mixed with other attractants has been found to have a positive effect on fish growth and survival rate. Betaine is also a very important substance for methyl donation and osmoregulation during the transfer of salmon and trout from freshwater to seawater. Similarly, L-alanine and L-glutamic acid can readily enter the citric acid cycle and be used for energy supply in fish and fish larvae. Moreover, L-arginine is an essential amino acid for fish, glycine is an important constituent of collagen and elastin, and inosine is a nucleoside and has vitamin activity in many fish species.