Temperature-dependent changes of growth rate and protein components were investigated for primary cultured cells derived from goldfish caudal fin. When the culture temperature was shifted from 20°C to 35°C and 40°C, the growth rate was increased at 35°C as compared with that at 20°C, but no cell growth was observed at 40°C. The differential scanning calorimetry demonstrated the onset of the endothermic reaction for goldfish cellular components at 40°C. Therefore, the temperature shift to 40°C was found to be of severe heat shock for goldfish cultured cells. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis revealed that, although expression of 70-kDa components was slightly induced at 35°C, the temperature shift to 40°C markedly induced the expression of the 30-kDa component in addition to that of 70-kDa component. The N-terminal amino acid sequencing identified the 30- and 70-kDa components to be heat shock protein (Hsp)–30 and Hsp70, respectively. Northern blot analysis revealed that the enhanced Hsp30 messenger ribonucleic acid (mRNA) levels were only observed at 40°C, whereas Hsp70 mRNA was slightly accumulated at 35°C. These results indicated that Hsp30 might have important functions under severe heat stress condition.