There is a great variability in results with regards to fasting-induced changes in the leptin system. In goldfish, no significant differences in either brain or liver leptin expressions are seen between control, overfed and fasting fish, suggesting nutritional status does not affect the leptin system in goldfish (Tinoco et al., 2012). Similarly, leptin expression is not affected by fasting in the liver of common carp (Huising et al., 2006a) (Cyrpiniforme) and Nile tilapia (Shpilman et al., 2014) (Perciforme) or in the brains of red-bellied piranha (Volkoff, 2015b) and pacu (Volkoff et al., 2017) (Characiformes). However, fasting/food restriction increases hepatic leptin expression in white-clouds mountain minnow (Tanichthys albonubes, Cypriniforme; Chen et al., 2016b), in most Perciformes examined (orange-spotted grouper Zhang et al., 2013, mandarin fish Yuan et al., 2016, and mackerel Scomber japonicus Ohga et al., 2015, European sea bass Gambardella et al., 2012), in Arctic charr (Jørgensen et al., 2013) and Atlantic salmon (Rønnestad et al., 2010; Trombley et al., 2012; Moen and Finn, 2013) (Salmoniformes). In contrast, decreases in leptin expression are seen in liver of zebrafish (lepA) (Gorissen et al., 2009) and striped bass (Morone saxatilis) (lepB, perciforme) (Won et al., 2012) and intestine of red-bellied piranha (Volkoff, 2015b), and in blunt snout bream (Cypriniforme), higher feeding rates are associated with increased leptin pituitary expression (Xu et al., 2016). Whereas plasma leptin levels increase following fasting in rainbow trout (Salmeron et al., 2015; Johansson et al., 2016; Pfundt et al., 2016), Atlantic salmon (Trombley et al., 2012) and fine flounder Paralichthys adspersus (Pleuronectiforme) (Fuentes et al., 2012, 2013), they have been shown to decrease in earlier studies in fasted burbot (Lota lota) (Gadiforme) (Nieminen et al., 2003) and green sunfish (Lepomis cyanellus) (Perciforme) (Johnson et al., 2000).