Determination of the age structure, Growth models from sand goby (Neogobius pallasi Berg, 1916) in the Kaboodval, Zaringol and Shirabad Streams.

The purpose of this study was to determine the age structure, Growth models and it’s variation from sand goby Neogobius pallasi, in Kaboodval, Zaringol and Shirabad Streams. For this purpose,‏104, 30 and 62 specimens were studied in three streams, respectively, in summer 2008. Both male and female comprised five age groups (0+ - 4+). The maximum lengths were 137.55, 114.1 and 137.97 mm (TL) respectively. The most frequent age was 1+. There were only significant differences in sex ratio of specimensin the Shirabad Stream (p< 0.05). Growth model were positive allometric for specimens of the Kaboodval and Zaringol Streams (b>3) but in the Shirabad Stream was isometric (b=3). Based on the von Bertalanffy growth model, L∞ and Kin the Kaboodval, Zaringol and Shirabad Streams were (L ∞ = 143.7 K = 0.774, L ∞ = 122.1 K = 0.777 and L ∞ = 147.3 K = 0.66) and also the growth performance Index(φ), were 4.20, 4.06 and 4.15 respectively. The highest values of condition factor were observed in the Kaboodval and Shirabad Streams (1+), in the Zaringol stream (3+) an it’s minimum was for age group (0+) in three streams. After 2+ year age, significantly decrease in growth rate was observed. The stressful ecological conditions of Rivers in comparison with Sea ecosystems including of rapid changes in flow rate and human manipulation in environmental factors of River, may have some influences on the reducing longevity or eliminating the elder samples in population.