This is an overview of the hormones which may be involved in food intake control in fish, and some hypothetical pathways of their action are given based on mammalian knowledge. Most of the observed effects of these hormones may result from four types of mechanisms, each hormone acting by one or several as follows: (1) hormones could have a direct effect on central nervous system centres, associated with food intake behaviour or via vagal afferent neurons; (2) an indirect effect may occur via the gut which slows gastrointestinal transit, thus resulting in stomach distention which activates vagal afferent neurons; (3) they could have an indirect effect, acting directly on intermediary metabolism via glucose, free fatty acids or amino acids mobilization or storage; (4) the last possible pathway is an indirect effect by modifying directly or indirectly secretions of other hormones involved in food intake control. Some of these hormones (CCK, PYY, glucagon, adrenalin) act as short-term factors which regulate meal ingestion and are generally inhibitory factors. On the other hand, other hormones (GH, TH, and leptin) require more time to modify food
intake behaviour, and appear as stored calorie regulators. However, the orientation of hormones to short-term or to long-term action is not always clear as it has been noted for insulin and glucocorticoids, and may depend on the hormonal and metabolite environment.