For several years, synthesis hormone and antibiotics have been in use in enhancing growth and well-being in fish culture, however there had been apprehension among fish consumers as to the possible detrimental effects of synthetic hormones to human health. This led to the band on the use of these synthetic products in major countries of the world. This development led to search for natural alternatives that are effective, readily available, cheap, environmental friendly, and with little or no adverse effect on the general physiology of the fish. Thus, the use of plant extracts (phytoadditives) became a major focus in fish culture. This book described some of the plants that have been used in aquaculture, phytoconstituents, methods of preparation of phytoadditives, effects of some of the plant extracts on growth, blood and organs of fish. The quality of feed has a direct effect on the physiological activities of an organism. It is therefore very important to establish a baseline information on the histopathological, haematological and growth effects of some plants extract used as phytoadditives in aquaculture.