اثرات عوامل هيدرولوژيك وفيزيكوشيميايي رودخانه خشكرود بر مهاجرت ماهي سفيد (Rutilus frisii kutum)

Effects of hydrological and physicochemical factors of Khoshkrood river on Kutum {Rutilus frisii kutum kamensky) migration

The kutum (Rutilus frisii kutum) is an endemic fish of Caspian Sea, which enters to fresh water because of spawning after attaining maturity, and it migrates to Khoshkrood lower area. The purpose of this research was to determine the effects of physical-chemical factors such as water discharge, temprature, pH, soluble Oxygen, carbon dioxide, and transparency of fresh water on kutum reproductive migration; and was also the most appropriate measure of these factors in the maximum period of migration. For this aim, the values of the mentioned factors were measured within to months four times a day during the migration season. In this research, 81 percent of the captured fish were male, 16 percent of them ready to breed and 3 percent of them were immature. The obtained results showed that atmosphere temperature effects water temperature; so it has an direct influence on migration rate. The optimum range for atmosphere temperature was determined 7-16 degrees Celsius at night and 11-17 degrees Celsius during the day. Also the appropriate extent of water temprature was determined 12.75-15 degrees Celsius at night and 13-16.25 degrees Celsius during the day.With due attention to the most depth of the river which was 75 cm, optimum value of transparency index was determine 73.5 cm at night and 62-68.5 cm in day. The appropriate range of soluble oxygen was counted more than 4 mg/1. The appropriate range of soluble carbon dioxide in the water at night was counted 1-6 mg/1 and 0.75-3.75 mg/1 in day. The most appropriate pH extent in water at maximum period of migration was counted 7.5-8 at night and 8-8.5 in day. Water discharge in the river in the maximum priod of migration 0.5-1 m3/s was counted during days and nights. In this research on the basis of T-test, the measure of capturing and migration rate in dark extent comparing with lighting exent was in the highest extent (P<0.05). It shows the high negative phototropism in kutum. Keywords: Migration; Kutum (Rutilus frisii kutun ); Khoshkrood