The Gold-Spotted mudskipper Periophthalmus chrypsospilos is a potential aquarium pet living in the mudflats in coastal and estuarine regions, but populations of this mudskipper within the Mekong Delta are facing extirpation risks due to indiscriminate harvesting for the growing aquarium and food-fish trade. Consequently, this research aims to provide first reproductive references such as spawning type and season, length at first mature, batch fecundity, being used in conservation and artificially propagation research. Analysis results from 1,031 individuals (523 males and 508 females) reveal that the sex ratio of total individuals recorded is 1:1 (523 males and 508 females) (c²=0.22, p=0.64). The GSI values are found to exhibit a non-normal distribution (Shapiro-Wilk Test, NJ=0.87, p<0.01) and change by gender (Mann-Whitney U, Z=27.04, p<0.01), season (Z=6.17, p<0.01) and site (Kruskal-Wallis H, c²=40.72, p<0.01).  A combination of GSIs and the monthly appearance of mature gonads suggest that this species reproduces throughout the year, with a peak from July to October. This species exhibits sexual and spatial variation in the size at first maturity (L_m) as L_m is 6.2-8.6 cm in males and 6.4-7.3 cm in females. The batch fecundity (F=2,614 to 23,465 eggs/female) exhibits non-normal distribution (Shapiro-Wilk Test, NJ=0.96, p<0.01) and varies with site (Kruskal-Wallis H, c² =35.55, p<0.01), reaching the highest point at Dam Doi, Ca Mau (13,336±1,279 SE) and the lowest point at Tran De, Soc Trang (6,654±851 SE). In addition, F is directly proportional to body size due to high determination values of relationships between F and fish size (r²>0.64 for all cases). Information derived on the reproductive biology of this species can inform its conservation, sustainable exploitation, and ex-situ propagation.

Fishes were caught by hands for 12 months from April 2020 to March 2021 at four estuarine areas in the Mekong Delta. Tricaine methanesulfonate (10g/L) was used to anaesthetize the fish specimens which were washed under the tap and preserved in 5% buffered formalin before transport to the laboratory.