If your Sim catches an endangered fish in The Sims 4, you basically have two choices: release it or keep it.
Releasing the fish back into the water is the safer option, especially if your Sim wants to become famous.
Releasing endangered fish can increase your Sim’s reputation. Nearby Sims will also react positively to your Sim and may interact with them in a friendly way.
If you’re trying to build a good reputation, releasing endangered fish is an easy way to help.
Keeping an endangered fish can hurt your Sim’s reputation if you have Get Famous.
Nearby Sims may react negatively, including giving your Sim a disapproving look or being mean to them.
So if your Sim is trying to maintain a good reputation, keeping endangered fish in their inventory probably isn’t the best idea.
There’s one particularly strange exception if you own Island Living and Snowy Escape.
The Tuna Maki Roll recipe requires Bluefin Tuna, which your Sim has to catch in Sulani. The problem is that Bluefin Tuna is classified as an endangered fish.
So if you want your Sim to make Tuna Maki Roll, you actually need to keep an endangered fish instead of releasing it.
It’s a slightly odd situation because the game encourages your Sim to release endangered fish, while also requiring one of them for a specific recipe.
If you’re not interested in the recipe, though, you’re better off releasing endangered fish, especially if your Sim cares about their reputation.
Of course, if your Sim is a dedicated collector or fisherman, you might decide that having the rare fish is worth the consequences.