How can we look after our injured sturgeon?

You could use some aquarium salt for fresh water fish. Read the directions on the back and either add it to your pond (or the shallow tub he's in now) or mix it up in a gallon milk jug and gently flush out the wounds with it. You don't need to use all of it for flushing the wound. What the aquarium salt does is it helps minimize stress in injured/sick fresh water fish and helps rebuild the natural slime coat that may be lost from the injury. Good luck and Hope your sturgeon feels better soon!