Terpenes are a class of natural products consisting of compounds with the formula (C5H8)n where N ≥ 2. The basic unit is isoprene (2-methylbuta-1,3-diene). Terpenes are supplied to aquafeeds in blends as well as individually to improve immunity and increase resistance to abiotic and biotic stresses. However, toxicity studies of terpenes are not sufficiently complete. Many of the tested terpenes and terpenoids show their beneficial activity in a given dose range. However, many of the dose-response relationships are only fragmentary. This means that the low-dose range or the high-dose range is not adequately covered. As a result, the adaptive response to apparently harmful compounds or the adverse effect of apparently beneficial compounds is not covered; the physiological response potential of the treated animal is disregarded. The classic pharmacological regression technique of structure-activity relationships is rarely used to predict effects in the host based on the structures of the supplemented compounds and to improve the selection of future supplements. This shows that using artificial intelligence to select feed supplements for sustainable and prophylactic nutrition of aquatic animals may be superior to the regression technique and is waiting to be applied. As with the other classes of dietary phytochemicals discussed in previous chapters, epigenetics has been studied tentatively. Therefore, the remarks made in the previous chapters apply and need not be repeated here.