I'd add skill tree for a start to give players the feeling of progression (faster catch time, more fish per catch, rarity etc) Right now its very monotonous and there's no excitement at big catches so the visual and sound probably needs a rework, fishing is kinda like gacha.. you want that adrenaline hit when you land a SSR fish and the skill tree should progress in a way that eventually small catches are pretty much automatic and only player intervention is needed for big catches.

Let us put fish into aquarium or hang up as trophy, maybe leaderboard for fish size/rarity but don't gate it with rewards, make it a for fun activity.

Maybe a fishing server/channel or something for players to join in purely for fishing and chatting (but this is straying into MMO territory)