The Environmental Effect on Spawning Time, Length at Maturity and Fecundity of Kutum (Rutilus frisii kutum Kamensky, 1901) in Southern Part of Caspian Sea, Iran

Fish sampling were carried out using beach seines during the fishing season from early october 2006 to mid april 2007. the gonadosomatic indexes (gsi) in range and average for female and male were 0.03 to 40.28 (5.70 ± 6.48) and 0.13 to 16.71 (3.39 ± 2.33), respectively. the gsi indicated that the reproductions of r.f. kutum were occurred during march-april, with the highest average value of 6.52 for males and of 17.00 for females in april. fifty percent of length maturity (lm50%) at fl = 37.78 cm was recorded. the absolute fecundity ranged from 15,723 for a three-year old to 130,737 eggs for an eight-year old female, with a mean of 60435 ± 24889. the relationship between fecundity (f) and fork length (cm) was represented by the formula: fec. = 6616fl+25916. the von bertalanffy growth parameters was: ls=67.5cm, k=0.21 year- ', t0 =-0.10 for throw population of kutum. the maximum spawning migration into the rivers based on gsi occurred significantly in april but it be affected by environment of sea water layers. the results showed that the length at first maturity and fecundity of r.f. kutum reduced in southern part of caspian sea