Age and growth structure of Polynemus dubius Bleeker, 1851 (Polynemidae) in the Saigon-Dongnai lower course system

Abstract

The majority of specimens were collected from January 2010 to June 2012, and additional specimens were collected during 2016 in the Saigon-Dongnai lower  course system using different types of fishing gears (trawl net, human scoop net, gillnet, trammel net, dai, inshore stake trap net, etc.). To determine the relationship of age and growth, 120 specimens of Polynemus dubius were examined from January 2016 to May 2017. The results showed that the mean exploitable size was 13.06±4.24 cm (males: 13.51±2.71 cm; females: 15.64±3.21 cm; and immature: 7.40±1.38 cm) with the average weight of 21.54±15.93 g (males: 20.41±9.94 g; females: 30.98±15.82 g; and immature: 4.50±1.56 g). The mean condition factor (K) was significantly different between the males and females (males: 0.78±0.14 and females: 0.75±0.09). Age groups of males and females ranged from 0 to 3. The most common age groups were 1 to 2+ (accounted for 75% of total specimens). The length-weight relationship was calculated as W = 0.014L2.756 (R2 = 0.966) for females, W = 0.024x2.556 (R2 = 0.930) for males, and W = 0.033L2.446 (R2 = 0.966) for all fish (males, females, and immature).