Waste water discharge containing chromium can lead to chromium polluted regional water. Because of the accumulation and enrichment of chromium, fish and other aquatic organisms can be injured seriously in polluted water, and chromium can cause toxic effects or death in humans if ingested. Chromium mainly refers to Cr⁶⁺, which exists as a noncatalytic form or as potassium dichromate. Fish, such as loach and carp, are commonly used to detect chromium, but few reports have used fish cell lines. Previous studies have revealed that cells cultured are homogeneous, respond quickly, and are convenient to use. In this study, loach fin cell lines established from diploids and triploids (DIMF and TRMF) were used to assess the toxic effects of potassium dichromate . The purpose of this study was to establish suitable indicators to monitor chromium pollution. The concentration that inhibited 50% of the cells (IC50) was determined using the thiazolyl blue (MTT) method, the activities of three main antioxidants were tested with kits, the changes in cell nuclei were observed after Giemsa staining, and expression of the metallothionein () gene was measured by real-time polymerase chain reaction (PCR) analysis. The results showed that the 24-h IC50 values of DIMF and TRMF were (25.3±1.2) mol/L and (27.9±0.6) μmol/L, respectively; the sensitivity of DIMF to potassium dichromate was higher than that of TRMF, and the sensitivities of the two cell lines were higher than those of loach in vivo. Superoxide dismutase (SOD) activities in the two cell lines increased as the potassium dichromate concentration was increased from 0 to 30 μmol/L. Glutathione peroxidase (GSH-Px) activities increased in the two cell lines as the potassium dichromate concentration was increased from 0 to 20 μmol/L; however, GSH-Px activities decreased when concentration was 30-40 μmol/L. Glutathione S-transferase (GST) activities in the two cell lines decreased gradually as the potassium dichromate concentration was increased. Overall, the enzymatic activities of DIMF were lower than those of TRMF. Potassium dichromate caused nuclear damage and micronuclei formed. The maximum rates of micronuclear formation in DIMF and TRMF were 7.33‰ and 8.00‰, respectively when the potassium dichromate concentration was 40 μmol/L. The rate of micronuclear formation was lower in DIMF than that in TRMF. The real-time PCR results showed that MT gene expression in the control group was very low, but increased significantly in response to potassium dichromate stress (<0.01). MT gene expression was maximal in response to 30 μmol/L potassium dichromate and was 49.9-and 50.7-times higher than that of the control group, respectively. However, the difference between DIMF and TRMF was not significant.