Hey, this game was pretty fun! Its a really addicting game loop and also pretty challenging! I liked how you did the controls, but I think if the speed and movement was constant then it would have made it a bit more "arcadey" and challenging if that makes sense(forces the player to keep moving and is always put at risk of getting eaten by other fish). Thats how I thought the game controlled at first, but it seems like velocity is handled by a speed variable multiplied to a direction with clamping. Its a bit weird, since there isn't really a keyboard way to stop the fishes momentum, but letting go of the keyboard slightly slows it down until it stops moving after a few seconds. Upon writing, this is the biggest nitpick of nitpicks I have ever made, but I think either setting the player at constant velocity from start to end would have made it more fun and risky in my opinion, but the movement is fun nonetheless! I also like the fact that the fish shrinks as time passes without you eating another fish, so you are punished for either waiting too long and you are never safe from being eaten.
Although you didn't make the art and audio of the game, I have to say that you've done a really good job of putting all these individual assets together to make a visually and audibly pleasant game! Even though all the assets came from separate creators and have different styles, the game doesn't give off that impression, so good job on that!
Overall, I had a lot of fun playing! I feel like maybe the fish you play should always start at the same size since its a highscore game. Although being a big fish makes your hitbox bigger and makes players have less time to react to threats overall, I still think there is a bigger advantage to play as a big fish than the little fish in the beginning. With some adjustments on gameplay, this could be a real cool highscore game! Great job!