That looks pretty serious. Not sure if any of his internal organs were damaged from that picture, but that wound looks very bad. Melafix and salt is all you can do at this point. Make sure you do water changes every other day at 40-50% to avoid any added stress from high ammonia lvls and parasites. Best of luck
It don't look good and may not make it, if its just fins and scales its gonna be OK but when there are injuries to the abdominal region that worries me. Wish you luck as Asians are expensive and hard to get hold of in Oz