Idea myself and @Beardageddon expanded on came up with.
Idea
Ships have a fish tank to store a player caught fish.
Why/Benefit
This can be used as a free pet for player that can't/don't want to buy a pet. Also it can be used as a crew mini game to look after a fish to grow it to a trophy size fish.
Mini Game
Looking after the fish (only works on the non-trophy fish size) it will grow in size to the trophy type.
Growth rates and the bait used to feed it - will depend on the bait needed to catch it and its rarity. Eg very rare fish will take longer to grow as not to shortcut to catching a rare trophy type fish.
A fish can be removed from / added to the tank at any time and used/sold as a normal. Once a fish is removed from tank any growth effort is lost - so no need to store progress on the fish - Grow progress can be stored on the fish tank while a fish in stored.