Fishing roguelike is an awesome idea, and you executed it very well. I liked the different levels of fish, and (presumably) how upgrading to further reel lengths will allow you to get fish with more and more energy. I also like that you tied movement speed, round time, reel length, and energy per fish to the end-of-round upgrades.
I could not for the life of me get past round 4. I just kept getting sardines and anchovies. I know I'd been fishing a lot, but I didn't think I killed all the clown fish already... :( Having some indication of what sides of the island are better to fish in for the day (or moment-by-moment, it could change throughout the day) would be helpful and give me a reason to walk to locations that weren't just immediately south of the cooking pot (quickest travel time :)). I also reeeeallly wish that any unspent energy carried over to the next day; it gives the player more opportunity for decision-making and doesn't punish them for having leftover energy that isn't a multiple of 5. For example, I absolutely would have foregone some basic-tier upgrades in favor of guaranteeing that I could make it past the next round.
You've got something really cool here, I could totally see it being a full game on Steam! Trying to collect all the fish and striving to get off the island is a really satisfying game loop.