Effect of temperature on thermal stability of the crude alkaline proteases from goby (a), thornback ray (b) and scorpionfish (c). The temperature stability was determined by incubating the crude extract at temperatures from 30 to 70°C for 1 hour. The residual enzyme activity was measured under the standard conditions assay at different times. The original activity before preincubation was taken as 100%. Values are means of three independent experiments.