Whether fish venom arose 18 times, or 15, or 20, that’s a big contrast to other animals that use venom: In snakes, venom appears to have evolved only once. Fish experts say the distinct origins of fish venoms make sense because, unlike snakes, which always use their teeth, fish deliver venom in diverse ways. But still, the multiple evolutions of fish venoms mean that each group of venomous fish probably makes venom components that attack their victims differently.