No, we haven't found new fisheries to exploit on the Red Planet.
Mars, Inc. is the source of sustainable cat food, see the blue fish on the package (left).
Now you can spend your pet food dollars (or euros) on a cat food that doesn't hurt the ocean.
Leaving aside the debate on the sustainability of keeping pets, if you're going to have pets then it's good to have sustainable pet food options.
I'm sure somebody will say that the fish in catfood is better delivered to hungry people, and so it's not sustainable if it's eaten by a cat when people need food. But I don't think cats get the best fish that people want.