Tricking enemies into running into the coral and each other is a creative mechanic. Also nice art and sound effects.
I felt like the text between the battles wasn't the most interesting.
I feel like onboarding players could be a bit smoother. For my first play, I read all the tutorial text, which felt like too much text to throw out all at once. Then I was just shooting my goldfish at the sunfish trying to eat me (which did nothing but waste my troops). I started using the special fish to kill them, but that uses up your fish quickly, so I started clustering the enemies and using the puffer fish to kill a bunch at once, which was easy since the enemies move so slow for the first few battles. It wasn't until I reread the tutorial did I understand that you bait the enemies into the coral with the normal gold fish to easily kill 3+ per troop, which completely changed the gameplay since then you could kill 3+ sunfish per one goldfish and never have to use the special fish.
I wish the goldfish clustered around you better instead of getting stuck behind each other in a line, making them easy targets to get stuck behind an obstacle or all get eaten at once. Maybe have each fish want to move both towards you (the monarch) as well as away from each other (weak repelling impetus). This might help them spread out around you.