Although a lot of work has been done, several important questions have yet to be addressed: e.g. what are the interactions between leptin and other ‘metabolic’ hormones like insulin, ghrelin and CCK? Does the single leptin receptor serve as receptor for both leptin-a and leptin-b, are mechanisms downstream of the receptor determining factors or maybe is there an as yet undiscovered leptin receptor in the ample genome repertoire of fish? Moreover, interesting avenues of research not further discussed here include leptin's effect on angiogenesis (that may be important in the adaptive response to hypoxia), leptin's involvement in the immune system (Mariano et al., 2013) and bone physiology.