Effects of fasting on the gene expression of appetite regulators in three Characiformes with different feeding habits (Gymnocorymbus ternetzi, Metynnis argenteus and Exodon paradoxus).

In order to assess potential interspecific differences in the endocrine mechanisms regulating feeding in Characiformes, we used three fish species with different feeding habits: two Characidae, the omnivore black widow tetra and the carnivore bucktooth tetra, and one Serrasalmidae, the herbivore silver dollar, as models. cDNAs encoding for appetite-regulating peptides (orexin, cocaine and amphetamine regulated transcript CART, cholecystokinin CCK and leptin) were isolated and their tissue distribution examined. The protein sequences of the three species showed most similarities with those of other Characiformes, followed by Cypriniformes and Siluriformes. mRNAs of all four peptides were expressed in the brain. Orexin, CCK and leptin mRNAs were widely distributed in peripheral tissues of all species. CART mRNA displayed a wide peripheral distribution in bucktooth but was predominant in brain in black widow tetra and silver dollar. In order to assess possible interspecific differences in the response to fasting, we compared the expression of these peptides in fed and fasted fish. Fasting induced increases in orexin expression in all species, but decreased brain CART and leptin expressions in silver dollar only. In the intestine, fasting induced a decrease in CCK expression in silver dollar and black widow, and a decrease in leptin expression in bucktooth. Our results suggest that, in Characiformes, different responses of appetite-regulating peptides to fasting are related to both feeding habits and family. The results of this comparative study provide new insights on the regulation of feeding of economically important Characiforme species, which might be valuable for their management and farming.