Purified trypsin from goby migrated as a single band in SDS-PAGE (Fig. 1a) and native PAGE (Fig. 1b), indicating the homogeneity of the enzyme and confirming that the purified trypsin had only one isoform. The molecular weight of trypsin was estimated to be 23.2 kDa based on SDS-PAGE (Fig. 1a), corresponding to that determined by gel filtration. Most of fish trypsins have been reported to have molecular weights in the range of 23–28 kDa. The molecular weight of Z. ophiocephalus trypsin was similar to those from other fish species, such as walleye pollock