Population dynamics of invasive blackchin tilapia (Sarotherodon melanotheron) in selected urban and mangrove-associated canals of Bangkok, Thailand

WEERAWICH WONGROJ (Prasarnmit Elementary Demonstration School, Srinakharinwirot University. 114 Sukhumvit 23, Khlong Toei Nuea, Watthana, Bangkok 10110, Thailand)
KHANIN WONGROJ (Newton Sixth Form School. SiamScape Building, 215 Phaya Thai Rd, Pathum Wan, Bangkok 10330, Thailand)
ARIN NGAMNIYOM (Faculty of Environmental Culture and Eco-tourism, Srinakharinwirot University. 114 Sukhumvit 23, Khlong Toei Nuea, Watthana, Bangkok 10110, Thailand)
RUTHAIRAT SIRIWATTANARAT (Faculty of Science and Technology, Suan Sunandha Rajabhat University. 1 U Thong Nok Rd, Dusit, Bangkok 10300, Thailand)

Biodiversitas Journal of Biological Diversity
Vol. 27 No. 9 (2026)

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.