Lieutenant Commander Data admires a Ba'ku fish
The Ba'ku fish was a type of fish found in lakes on the planet Ba'ku.
In 2375, after detecting some curious readings, Lieutenant Commander Data stepped into a Ba'ku lake in an effort to ascertain the source. As he was scanning, a fish swam past him and he used his tricorder to scan it. After stroking the fish, he moved on. (Star Trek: Insurrection)