I think you tacked the visual aspect. Details like drawing the valley puts the player in context without noticing, and it is a good starting point for a platform such as a Game Boy, which nature didn't allow it to render very complex graphics.
The idea pretty clear, although I would have places the FISH button before the FIGHT button. As we usually read from left to right, users will be prone to hit the left button first. As it is to the interest of the player that Agros is as strong as possible, having a tendency to train it first instead of throwing it against the enemies seems coherent.
It took me a while to get the fishing mechanic. I though it was about luck, like a casino game. It would be better to change the way the player fishes to a more dynamic, visual output. Maybe one of those bars with a moving marker, which compel you to press the button when they are at a given stage of the line. Something like this, being << the moving marker:
[:::::::::::[HIT HERE]::::::::::::::::::::::<<::::::::::::]
While fighting, you would copy Pokemon and give some input about the result of the attacks. So if an attack fails, make the "You fail" redundant. When you hit, it could say how much damage you made. So the player has an idea of what is going on under the hood ;)