Life-history Aspects of Caspian Shemaya Alburnus chalcoides in Two South Caspian Rivers (Siahroud and Gorganroud)

摘要

Specimens of A. chalcoides caught in Siahroud (central of south Caspian Basin) and Gorganroud (east of south Caspian Basin) during spawning season from February to August 2007 were examined for life history attributes. The fish had a 5-year life cycle in the rivers and grew allometrically, being negative allometric for males of the Siahroud and positive for both males and females of Gorganroud and for females of Siahroud. The von Bertalanffy growth functions were L-t=370.08(1-e(-0.15(1+0.70))) for males and L-t=432.52(1-e(-0.11(t+1.21)) for females in the Siahroud and L-t=371.79(1-e(-0.14(t+0.96)))) for males and L-t=436.10(1-e(-0.11(t+1.34))) for females in the Gorganroud. Overall sex ratio was unbalanced in favor of females in the rivers. The GSI indicated that reproduction of Caspian shemaya occurred between April-July in the Siahroud and March-June in the Gorganroud, peaking in May in both rivers. The absolute fecundity ranged between 1,674-38,340 eggs with a mean of 8,426.25 eggs in the Siahroud and between 623-17,263 eggs with a mean of 4,214.70 eggs in the Gorganroud, while relative fecundity ranged from 23.28 to 598.86 eggs/g with an average of 211.68 eggs/g of body weight in the Siahroud and from 12.11 to 696.38 eggs/g with an average of 111.60 eggs/g of body weight in the Gorganroud. Mean egg diameter in the Siahroud was 1.40 +/- 0.14mm and 1.27 +/- 0.27mm in the Gorganroud. Comparisons of the results imply that many aspects of life history of Caspian shemaya are different markedly among the rivers. The differences were thought to have emanated from differences in habitat characteristics.