You can also check in your Critterpedia to determine

Now that it’s May, new schools of fish and swarms of bugs are available to catch in Animal Crossing: New Horizons on Buy Nook Miles Tickets Switch.

There’s no rush to catch any of them, as they’ll stick around for for for much longer than a month, but confirm you donate any new finds to Blathers to end your Museum. you'll tell when you’ve caught a replacement creature because your character will exclaim “Yes!” before they say the bug or fish’s name.

You can also check in your Critterpedia to determine if you’ve donated the bug fish or not. If you've , there will be slightly owl icon next to the critter LOLGA name.