The size–age structure, growth, and maturation of the spotted catfish Arius maculatus (Thunberg, 1792) from the Hau River estuary, Mekong Delta, Vietnam, were studied for the first time. A total of 460 fish specimens collected from January to March 2019 were examined. The annuli on the otoliths were visualized; their formation may be related with the alternation of the dry and rainy seasons. The male to female ratio in the catches was 1 : 1.81. The proportion of males decreased in the older age groups. The maximum total body length of the females was 21.9 cm; for the males, it was 23.7 cm. The maximum recorded age of females in catches was 7+; for males it was 8+. No inter-gender differences in growth were detected. The parameters of the von Bertalanffy equation for both sexes according to empirical data were as follows: L∞ = 28.3 cm; k = 0.15/yr; t0 = –1.03 yr; growth performance index, φ = 2.08. The coefficients of the relationship between mass and length were as follows: a = 0.0054; b = 3.22. Maturation began at a body length of 13 cm at an age of 3 yr and ended at a body length of 18 cm at an age of 6 yr; 50% of the individuals became mature at a body length of 15 cm at an age of 4 yr. No inter-gender differences in the timing of maturation were found. A. maculatus from the Mekong Delta is characterized by a low growth rate compared to other populations, which may be associated with the labile habitat conditions in the estuary zone.