A variation on 'Captain's coming' game with a water/ocean theme
The fish (players) swim around the sea (defined play area). When the leader calls out commands, players perform the appropriate action:
"Sharks" - bare teeth and snap ferociously
"Octopus" - get into pairs and sit back to back, waving arms and legs to make octopus tentacles
"Starfish" - lie flat on the ground/floor, spreadeagled
"Fishing nets" - converge in a group around the leader.