The Blanakan River is habitat for many fish species including river catfish (Mystus sp.). River catfish is freshwater fish that can survive in polluted aquatic environment. This fish is also consumed by people living near the river. In fact, Blanakan river is polluted by human activities such as agricultural, transportation and mining activities which make the waters may be exposed by heavy metals. Correspondingly, this study aims to determine the size variation of river catfish and its relationship with Cadmium (Cd) and pH parameter in water. Water and fish samples are collected from two stations. The pH was measured directly from water as well as length and weight of fish. The concentration of Cadmium (Cd) in water was analyzed using AAS (Atomatic Absorption Spectrophotometer). The result showed that the value of pH and Cd concentration were 5.78 – 6.64 and 0.03 ppm – 0.10 ppm respectively. While the ranges for fish length and weight were 13,20 cm – 13,59 cm and 30.69 gr – 34.7 gr. To conclude, the increase of pH can increase the size of fish. In contrast, the increase of Cd reduces the size of fish.

Catfish, cadmium, metal, pH, river