Comparative study of age and growth pattern in two riverine and marine populations of Neogobius fluviatilis pallasi from ZarrinGol River and Gomishan lagoon

Age structure and growth of the Caspian sand goby (Neogobius fluviatilis pallasi) in two populations from ZarrinGol River and Gomishan lagoon was studied with monthly sampling from March 2009 through June 2010. 320 fish from ZarrinGol River and 263 fish from Gomishan lagoon were caught. Male: female ratio was 1male: 3.4 female in ZarrinGol River. No significant differences were observed between abundance of male and female in Gomishan lagoon (P>0.05). In ZarrinGol river males were divided into 3 age classes of 0+ to 2+ and females into 4 age classes of 0+ - 3+. In Gomishan lagoon both males and females were categorized in 3 age classes of 0+ to 2+. Age class 1+ was the most abundant class of fish in both sexes and populations. Mean total length (TL) of males and females in ZarrinGol River were 7.5 ± 2 and 8.2 ± 1.7 and 9.7 ± 1.1 and 8.2 ± 1.4 in Gomishan lagoon respectively. Growth pattern in ZarrinGol River was positive alometric for both sexes and isometric in Gomishan lagoon. Condition factor varied in both populations in different months and age classes. Comparison of condition factor for both sexes in two populations showed no significant differences in age class 0+ while there were such differences in age classes of 1+ and 2+. Values of the condition factor were higher in ZarrinGol population.