Catching strange fish in Animal Crossing City Folk?

[Slycat]

There is a strangely large fish in the ocean and sometimes around rivers in AC:CF. Sometimes when you try to catch it, it will act like it is on the line, but when you press A to catch it, it escapes and swims away. It longer and slimmer than a tuna and a stringfish--how do you catch it?

 

[Pinkie]

You got to catch it in the ocean when it is raining