As his dad is a marine scientist, I found a 'fishbowl' hat in 101 Designer one-skein wonders. It is knitted as a tube with a knitted 'lid' inserted to close off the top- to give the notion of the rim of a bowl.
I used a ball of what I think is a wool/alpaca mix (not sure where that label went). The fish are pretty subtle in the wool, but will be sufficiently visible on the head.
To finish off the present, I made a bag in blue denim - those with good memories might recognise the leg of my jeans left over from the denim bags made last Christmas. The appliqued Holden rally car was from the One Stop Fabric Shop . I used elastic rather than a drawstring in the top in the hope Ed might open it himself.
Banana, bear, fish, car - I haven't exactly achieved a theme!
Maybe next time.