Zebrafish (Danio rerio) possess two kisspeptins, kiss1 and kiss2 and their respective receptors (KissR1) and KissR2]. In the brain of zebrafish, Kiss2 is expressed in the preoptic-hypothalamic area, and Kiss1 is predominantly expressed in the habenula, an evolutionarily conserved epithalamic structure. KissR1 is expressed only in the habenula, while KissR2 is widely distributed in the brain, suggesting that the two kisspeptin systems play specific roles in there. The habenular Kiss1 is involved in the modulation of the raphe nuclei and serotonin-related behaviors such as fear response in the zebrafish.
