I have mixed feelings about this. On one hand the controls (both keyboard and phone) are simple and intuitive. On the other hand the difficulty is frustrating and the lack of scoring mechanics makes the game unrewarding.
- Have bigger fish lose interest after some time.
- Make it so smaller fish don't dodge so well. You could perhaps add some variation where different fish can turn faster than others, making it easier to catch some than others. Or make it so that a fish can dodge for some amount of time but then becomes tired and easier to catch.
- Make it so the player's fish grows over time and perhaps display some kind of score counter so the player knows how well they're doing.
- Give the player a larger field of view.
- Some sound effects and music would be nice.
- Different graphics and colors for different fish would be nice. Perhaps different shapes could indicate how quickly a fish can turn or how fast it can move.
Currently it's advantageous to make slight turns and to be an opportunist, only catching fish you're already lined up with instead of making sharp turns to catch a fish that's about to get away. This is partly because sharp turns can put you in harm's way of larger fish and partly because by the time a smaller fish has made a sharp turn it's basically impossible to turn perfectly enough to lock onto them and chase them down.
This creates an interesting risk/reward opportunity if you could chase a really hard to catch fish to exhaustion; you would put yourself at risk by making sharp turns while being chased by other fish, but if you can keep the chase up long enough you could get rewarded with big points.