There's No Such Thing as a Fish
You are more closely related to a lungfish than a lungfish is to a trout. "Fish" isn't a real taxonomic group — it's paraphyletic, including some descendants of a common ancestor but not all of them.
The tree spans 500 million years. Jawless hagfish diverged first. Sharks split off 420 million years ago. Then came the enormous diversity of bony fish that dominates today. Seahorses are fully bony fish despite looking alien. Electric eels aren't eels — they're knifefish, closer to catfish. Flatfish start life swimming upright before one eye migrates to the other side of their head.
114 species from hagfish to tuna, covering roughly half of all vertebrate diversity in one game.
Did you know?
- *Technically, there is no such thing as a fish in strict taxonomy: humans are more closely related to lungfish than lungfish are to salmon.
- *Electric eels are not true eels; they are knifefish, more closely related to catfish and carp.
- *Hagfish are among the oldest living lineages of vertebrates, with fossils dating back over 300 million years.
- *Flatfish are born symmetrical but during development one eye migrates to the other side of the head.
- *Seahorses are fully bony fish that happen to swim upright, and the males are the ones that carry and birth the young.
What is GuessKin?
GuessKin is a free daily guessing game built on real-world taxonomy. Choose from over 20 categories and try to identify the mystery fish. Each guess reveals how closely related your answer is to the target through a shared classification tree.
How does it work?
Every fish in GuessKin sits on a taxonomy tree — a branching hierarchy that shows how things are classified and related. When you make a guess, the game shows you the nearest common ancestor between your guess and the answer. The closer that ancestor is to the answer, the warmer you are. The tree visualization grows with each guess, narrowing down where the answer lives and helping you triangulate.
How to get the best score
- •Fewer guesses is better. The ideal game is guessing it in 1. Every guess counts against your score.
- •Speed matters too. The timer starts on your first guess. Quick, confident answers are rewarded.
- •Read the tree. Each guess gives you real taxonomic information. Pay attention to which branch the answer is on and which branches you've already ruled out.
- •Start broad, then narrow. Your first guess splits the tree. Pick something that gives you maximum information, then drill into the revealed branch.
Each GuessKin category uses a real classification system. These aren't made-up groupings — they're the same systems scientists and specialists actually use. New categories are added regularly. Every category is free, with no accounts and no ads.