Stocking density influences brain arginine vasotocin (AVT) and isotocin (IT) levels in males and females of three-spined stickleback (Gasterosteus aculeatus)

Abstract

Arginine vasotocin (AVT) and isotocin (IT) are fish neurohormones produced in separate parvocellular and magnocellular preoptic neurons of Teleostei. Apart from well-established peripheral action as hormones they are important neurotransmitters in central nervous system in fish. In the present study, we examined an influence of stocking density on whole brain AVT and IT concentrations in males and females of three-spined stickleback (Gasterosteus aculeatus). In males, the highest AVT levels have been found at stocking densities of 10 and 30 individuals per 30-l tank. On the other hand, in females, AVT concentration was significantly higher in those kept alone. Brain IT concentrations significantly increased along with stocking density only in females and did not change in males. The sex-dependent responses indicate a different stimulation of AVT and IT neurons in males and females. Consequently, roles of the neurohormones in males and females exposed to stress of overcrowding must be different.