<![CDATA[Abstract. Wongroj W, Wongroj K, Ngamniyom A, Siriwattanarat R. 2026. Population dynamics of invasive blackchin tilapia (Sarotherodon melanotheron) in selected urban and mangrove-associated canals of Bangkok, Thailand. Biodiversitas 27 (9): d270909. https://doi.org/10.13057/biodiv/d270909. Invasive blackchin tilapia (Sarotherodon melanotheron) is now widespread in Thailand, but information on its local population dynamics in urban-coastal canal networks remains limited. We examined temporal and spatial variation in abundance, size structure, length-weight relationships, size-adjusted body mass, and environmental associations over 12 months at four canal stations in Bangkok. A total of 6,132 fish were collected using 480 cast-net throws and 48 standardized 5-min scoop-net operations, which were analyzed separately because of differences in gear selectivity. Cast-net relative abundance varied significantly among months (χ²: 68.89, df: 11, p<0.001), while scoop-net catches showed station-specific temporal patterns. The probability that a captured fish belonged to the predefined small-size class (≤8.1 cm standard length), used as an operational recruitment proxy, also varied strongly through time and among stations in cast-net samples but showed no monthly effect among positive-catch scoop-net visits. At the evaluated standard lengths of 5, 10, and 15 cm, local allometric slopes exceeded the isometric expectation (b: 3) and varied with fish length and station; size-adjusted modeled body mass showed corresponding station- and size-specific differences. Within stations, dissolved oxygen (OR: 1.153, 95% CI: 1.028-1.294) and turbidity (OR: 1.172, 95% CI: 1.054-1.302) were positively associated with the small-size proxy in cast-net samples, whereas addition of these predictors did not improve the corresponding scoop-net model (joint p: 0.804), indicating that the environmental associations were gear specific. The findings demonstrate continued occurrence and marked population heterogeneity at these preselected invaded stations and provide a quantitative basis for local population monitoring.]]>
