In Cypriniformes, early immunoreativity (ir) studies in goldfish showed the presence of MCH in neuron populations related to the regulation of feeding and of sleep and arousal (Huesa et al., 2005). In goldfish, central injections of MCH decrease feeding but have no effect on locomotor activity (Shimakura et al., 2006), anti-MCH serum treatments increase feeding (Matsuda et al., 2007a), and the number of certain hypothalamic neuronal cell bodies containing MCH-ir decreases in fasted fish (Matsuda et al., 2007a), altogether suggesting an anorexigenic role for MCH in this species. However, in Ya fish, MCH hypothalamic mRNA expression is higher in fasted compared to fed fish, suggesting an orexigenic role (Wang et al., 2016). Data on Gadiformes and Pleuronectiformes also seem to suggest an appetite-stimulating role for MCH: MCH brain mRNA levels increase during fasting in both Atlantic cod Gadus morhua (Tuziak and Volkoff, 2013a) and winter flounder Pseudopleuronectes americanus (Tuziak and Volkoff, 2012), and in cod fed diets with relatively high amounts of plant (camelina) material (Tuziak et al., 2014). In starry (Platichthys stellatus; Kang and Kim, 2013b), olive (Paralichthys olivaceus; Kang and Kim, 2013a) and Barfin (Verasper moseri; Takahashi et al., 2004) flounders, fish placed in light backgrounds have enhanced appetite and growth, which is concomitant with increased expression levels of MCH mRNA and/or numbers of MCH neurons in the brain. However, in medaka Oryzias latipes, transgenic fish overexpressing MCH have normal growth and feeding behavior (Qu et al., 1996) and in the scalloped hammerhead shark Sphyrna lewini, hypothalamic MCH mRNA levels are not affected by fasting (Mizusawa et al., 2012), suggesting little or no role of MCH in feeding regulation of Beloniformes and sharks.