Life history pattern of the Bitterling Rhodeus amarus (Bloch, 1782) in Siahroud River (southern Caspian Sea-Iran)

摘要

A total of 272 specimens of R. amarus caught in Siahroud River at the southern Caspian Sea from March 2006 to February 2007 were examined for life history attributes. Length-at-age was different between sexes. The von Bertalnffy growth function fit to back-calculated size at age data were: L_t= 94.16 [1-e~(-0.31)(t+0.321)]and L_t=92.33[1-e~(-0.32)(t+0.488)] for males and females respectively. WLR was estimated as W=0.0074TL~(3.4546) for males and W=0.0133TL~(3.0550) for females, positive allometric for both sexes. There was no significant difference from parity in the overall sex ratio. The reproductive season is extended from March to June, with a culmination point in April. Two kinds of eggs were found; small eggs measuring between 0.42 and 0.91mm with a mean value of 0.57±0.08, and large yolk-filled eggs ranged from 0.88 to 2.20mm with a mean value of 1.49± 0.24 (S.D.). The average absolute and relative fecundities were 329.74 eggs and 187.40 eggs g~(-1) respectively. Variability of life history patterns of the fish in the basin could be interpreted as species response to basin condition.