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.

Irisin in goldfish (Carassius auratus): Effects of irisin injections on feeding behavior and expression of appetite regulators, uncoupling proteins and lipoprotein lipase, and fasting-induced changes in FNDC5 expression.

Irisin is a peptide cleaved from the fibronectin type III domain containing protein 5 (FNDC5) gene that is secreted predominantly by muscle cells but also by other tissues including brain and intestine. In mammals, irisin has been shown to have thermogenic actions via the modulation of uncoupling proteins (UCPs) and to affect feeding and energy homeostasis via actions in brain, adipose tissue, liver, muscle and gastrointestinal tract. To examine the role of irisin on feeding and metabolism in fish, the effects of peripheral (intraperitoneal) injections of irisin on feeding behavior, glucose levels and the mRNA expressions of appetite regulators (cocaine and amphetamine regulated transcript CART, agouti related protein AgRP, orexin), UCPs and lipoprotein lipase LPL and brain factors (brain-derived neurotrophic factor , BDNF and tyrosine hydroxylase TH) were assessed in brain, white muscle and intestine.