Fishing in R/S/E is different to that of other games such as FR/LG etc. As soon as the "!" appears press A. It may or may not take you into a battle straight away. If it does yay. :3c If it doesn't, get ready to press A again. It'll come earlier each time. Remember to practice with the Old Rod since it's the easiest one, the good rod is helpful too. Fishing is difficult in these games, I'll admit. :P I remember having a lot of trouble with it. :3c