Fish Fillets NG, originally just Fish Fillets, is a puzzle video game developed and released by Altar Games in 1998. The game's goal is in each level to find a safe way out for both of the two fish. Fish Fillets is comparable to other sliding puzzle games such as sokoban and klotski, while it has a few additional elements and rules.
Source: Wikipedia, "Fish Fillets NG", available under the CC-BY-SA License.
Once upon a time there were two fish. They worked for a fishstitution so secret that even they didn't know its name. It investigated UFOs (Unidentified Floating Objects), searched through wrecks of land-based vessels known as "floating saucers" and carried out DIVER (Deeply Interesting and Very Expensive Research). One day, one particularly nasty UFO invaded the underwater realm, wreaking havoc as it zigzagged along the ocean floor. It struck the little house of the two fish and destroyed it beyond recognition. As our heroes set out on their quest to restore the peace, they learned that the Agency has put them in charge of eight different missions. Only when they complete them all do they have a chance to get back home. Their only consolation is the Agency's motto: The solution is out there…
Source: The Publisher Website.