Hormonal failure and osmoregulatory disruption in laboratory food-deprived Caspian kutum, Rutilus frisii larvae during brackish water challenge

Caspian Kutum, Rutilus frisii, is a valuable species in the Caspian Sea basin. With the aim of restocking, the Iranian Fisheries Organization (IFO) annually released millions of Caspian kutum larvae into the estuaries of the Caspian Sea. This study was conducted to evaluate the effects of starvation on fish during Caspian seawater (CSW) adaptation. Caspian kutum larvae (0.5±0.1 g) were divided into two groups; one was considered a control fed ad libitum during the experiment and another group was left food deprived. Both groups were continuously exposed to the CSW challenge (13 ppt) for 7 days and sampling was done on the second, third, fourth and seventh days after initiation of the CSW challenge. Different physiological factors, including hormones (cortisol, T3, and T4), gill Na+/K+-ATPase activity, whole body glucose and protein, gill protein, body moisture, and seawater preferences, were analyzed in each sampling time. The results showed that although fed larvae can successfully overcome the physiological changes imposed by the CSW challenge, the starved fish indicated significant failures in the most measured parameters and eventually demonstrated significantly lower salinity preferences. Therefore, it can be concluded that starvation may negatively affect the success of CSW adaptation. Since physiological impairment during the CSW adaptation period is directly related to the effectiveness of the restocking program, more studies about the feeding condition of Caspian kutum larvae pre and post-releasee and the nutritional status of recipient rivers are suggested.