Investigation of some hormones affecting osmoregulation of Lake Van fish ( Alburnus tarichi ) during reproductive migration

Abstract

Lake Van is one of the largest soda lakes in the world. The extreme characteristics of the lake greatly limit the animals living there. Lake Van fish (Alburnus tarichi Güldenstädt, 1814) is the only vertebrate species that has adapted to this environment. Lake Van fish migrate to freshwater every year to breed, after which, they return to the lake environment. The fish are exposed to different aquatic environments during migration. The endocrine mechanisms involved in the physiological changes during this migration are not studied in this species, yet. In this study, water and serum sodium, potassium and chloride levels in the lake, downstream and upstream to which Lake Van fish are exposed during reproductive migration were determined. Circulating cortisol, free triiodothyronine, free thyroxine, insulin-like growth factor-I, growth hormone and prolactin levels were also investigated. It was observed that the water ion levels decreased in the freshwater localities when compared to the lake localities, and the serum Na+ and Cl− levels decreased in upstream1 and upstream2, K+ levels stayed at a certain level in all localities. It was determined that the hormone levels differed in the upper regions of the river (upstream1 and upstream2), where spawning was completed, from the lake environment, where reproductive migration began. Results indicate that the studied hormones had direct and indirect effects on osmoregulation in the Lake Van fish with the physiological tendency to keep osmotic homeostasis, as occurs in other teleost species.