If you look further down this page, you will see something about the Maryan Garayan fish. I found more facts to add on to that cheat.

The First Thing is:theres another way to catch one.First you need to have beaten the Sun & Moon temple.Second is that you need a potato cake.Now,go to the Oasis in Muska Racka.You should see four fish spread out.Go for the biggest one.The Maryan Garayan is about 2 inches from the fishing sign.If it's not the right size then quit fishing,goto the sign,and fish again.If you noticed the fish will be different sizes,repeat this until you get the Maryan Garayan fish.

The Second Thing is:the Maryan Garayan is a very patient fish. It won't just swim over and grab the bait,it will go over,touch it,and stare at it for awile.So since theres four fish,get four potato cakes or try avoiding the others.When the M.G. pulls the floater under water,then pull it up and congratulations you just made over 500 Fishing Points.