Description:
<jats:title>Abstract</jats:title><jats:p>This study provided new knowledge on reproductive traits of the unique mudskipper <jats:italic>Periophthalmodon septemradiatus</jats:italic> that is also a potential aquarium pet. Fish specimens were obtained by using fishing rods at the muddy flat in tributaries of the Hau River from August 2017 to July 2018. Data analysis of a collection of 1,504 individuals (930 males and 674 females) showed that the sex ratio of this species was significantly different from the ratio 1:1. As mature gonads were found monthly during the study period, it is suggested that <jats:italic>P. septemradiatus</jats:italic> is an iteroparous species releasing eggs for a year‐round cycle. The fish length at first mature (<jats:italic>L</jats:italic><jats:sub>m</jats:sub>) showed an increase from estuary to upstream areas. Male <jats:italic>P. septemradiatus</jats:italic> had higher <jats:italic>L</jats:italic><jats:sub>m</jats:sub> values than that of females. Likely, the batch fecundity increased from estuary region (5,916 ± 312 <jats:italic>SEM</jats:italic> eggs) towards upstream area (11,451 ± 953 <jats:italic>SEM</jats:italic> eggs). The fish total length and weight values had strong positive relationships with batch fecundity, as shown by high determination values (<jats:italic>r</jats:italic><jats:sup>2</jats:sup>), suggesting that batch fecundity increased with fish size. This study provided more information on reproductive biology of <jats:italic>P. septemradiatus</jats:italic>, which can be utilized for fish population conservation and artificial reproductive study.</jats:p>