The alarming evolution which is now taking place in the pathology of aquaculture species, is of great concern to all farmers and the aquaculture industry in general. Today the whole fish/shrimp health picture is far more complex than it was a few years ago. More and more resistant bacterial strains are reported and viral diseases are becoming a major threat to tomorrow's industry viability, especially in shrimp culture. New regulations are decreasing the drugs available to treat pathogens. Vaccine development is rather slow and moreover ineffective in shrimp culture or for the first stages of fish. Therefore, fish/shrimp farmers will have to consider much more than before healthy husbandry procedures and adequate nutrition as the most important tools to ensure their business a secure future. This paper reviews the key nutrients involved in fish/shrimp health and immunology. The effect of vitamin C and E is well documented but other nutrients also play an important role such as astaxanthin, trace minerals (selenium, chromium, zinc, copper) and essential fatty acids. Apart from these key nutrients, anti-nutritional factors, diet formulation and processing techniques might also affect directly or indirectly the resistance of the species raised. Recently, a great deal of effort has been invested by industry and academia on the development of a new generation of products called immunostimulants. A large number of commercial products have reached the market in a desperate (and sometimes opportunistic) attempt to offer even a partial solution to the spreading of viral and bacterial diseases. However, the results obtained with these substances have not always been consistent and still do not bring a real efficient protection against diseases compared to vaccines. A review of some commercially available substances is presented and the difficulty of their evaluation is discussed.