Effect of reproductive migration time on some biological character of eggs in mahsfid (Rtilus frisii kutum kamenskii 1901)

This survey was done to determine some biological characteristics of eggs (including diameter، surface، volume، and surface to volume ratio) and hydrated eggs (including diameter، surface، volume، surface to volume ratio، yolk sphere، and perivitelline space and yolk sphere to perivitelline space ratio). 90 migratory population of Mahisefid، Rutilus frisii kutum were studied at 3 treatments (initial، middle، and the end of broodstock migratory time) in the Tajan river. Amplitude of egg diameter and its surface to volume ratio calculated 1. 92-2. 25 mm and 2. 66-3. 07 mm-1، respectively and for hydrated egg calculated 2. 41-2. 78 mm and 2. 16-2. 48 mm-1، respectively which was significant (P < 0. 05) at broodstock migration time and for egg and hydrated egg was minimum at end of migratory time and maximum at initial of broodstock migratory time. But it was invers for surface to volume ratio. Yolk sphere to perivitelline space ratio was 0. 79 ± 0. 13. It show that the yolk sphere is near to the half of the egg sphere and it can be the reason of Mahisefid breeding in water with median temperatures.