Whether carving a body or using a manufactured form, make sure the body fits the head.

When you are sure that your fish body and head are a good match, prepare the fish skin and mount.

If you are using Flex eyes, insert them in the head.

Attach the head using auto body filler.

You will have to hold the head in position until the body filler is firm or, if possible, insert wires in the eye sockets to hold the head position.

Grind the head transition if needed then fill the gap between the head and body with body filler.

Next, sand with heavy grit then medium grit sandpaper. Repeat if necessary.

Fill any pin holes or scratches with Apoxie Sculpt. It can be smoothed out with water on your finger.

Sand with steel wool, prime the head, set the eyes (if not already set).

Paint as you normally would.