Population and Age Structure of the Goby Parapocryptes serperaster (Richardson, 1864; Gobiidae: Oxudercinae) in the Mekong Delta

The goby Parapocryptes serperaster lives on the mud flats in estuaries and has been increasingly exploited as food fish in Mekong Delta, Vietnam, but little is known on its population, age structure and growth. This study aims to understand some basic parameters of its population biology and age used for fishery management and size-selective fishing. Based on monthly samples over a year, a total of 3002 fish were used for population structure analysis. Fish length distribution and otoliths were used for fish aging. The sex ratio of P. serperaster was near 1:1 and fish size at first entry to fishery was 14.6 cm. The longevity of this goby was 4.05 yr, but fishing mortality (1.57 yr(-1)) and natural mortality (1.51 yr(-1)) accounted for 51% and 49% of the total mortality (3.07 yr(-1)), respectively. Relative yield-per-recruit and biomass-per-recruit analyses revealed the levels of maximum exploitation yield (E-max = 0.83), maximum economic yield (E-0.1 = 0.71) and the yield at 50% reduction of exploitation (E-0.5 = 0.37). Readable otoliths from female (n=164) and male (n=196) gobies with proper otolith morphometry were used for age identification. The mean age estimated by reading otolith annual rings matched the age estimate from length frequency distribution. The otolith morphometry is a reliable method to age this goby and possibly also applicable for other tropical gobies. The fishery analysis indicates that this goby stock is not overexploited and shows high population recruitment in the Mekong Delta.