(I) Fish farming, which is practiced in many countries, has developed into an industry in recent years. (II) This has made scientific research into fish biology of vital importance. (III) Hence, advances in disease control and in fish nutrition are likely to be impressive in the years ahead. (IV) Fish farming has succeeded only where it can compete with other forms of food production in terms of costs. (V) Moreover, for most fish species, genetic improvements through breeding have already been achieved to make the industry profitable.