a problem and frustration i had with the game. you only hit a fish, if you aim at it directly. the tip of the spike is only capable of catching fish when it reaches max length. so you need to perfectly predict where small fish will be so you can aim there or you will never hit. more fun would be, if the spike tip touching a fish would catch it, no matter if its extended to the point you aimed at or not.
plants are either also affected by this issue, or this is an issue because of plants. hitting plants is bad. your spike retracts upon contact. contact can however only be made, if you shoot the spike at the plant. the spike can go through the plants otherwise with no problem. this makes plants a non-factor in gameplay. the spike hitbox was either done intentionally to make plants less annoying, or this is an oversight with how the spike works.
jellyfish also have the same issues. the mass jellyfish stage would be impossible with a full hitbox spike, yet is incredibly easy with a spike with only a hitbox when the tip reaches the targeted area.
either way i think it ruins the game, as you dont really feel powerful. you are spending minutes trying to kill tiny fish that are zooming across the screen and are nearly impossible to hit.
another contributing factor is that the spike is slow. it makes it impossible to hit fast targets, due to the small hitbox of the spike, precision needed and slow extension speed of the spike.