General:

• all of them have jaws that can unhinge
• based on real species of fish. Between parents of different fish species, 50/50 of being born either one
• usually native to the same place their fish species is, but known to migrate
• get fuckin BIG
• no breasts
• all carnivorous
• god worship
• feral but sapient
• fucking scary as hell
• brutality of the ocean
• babies are called pups
• they sing good, but also use sound waves to fuck with prey
• those who eat humans are known as Man Eaters

Biology:

• gills
• scales/chiton/etc encroaching on their skin depending on what species their lower half is (i.e. isopod lower half with chiton plating along arms)
• REAL-WORLD species lower half
• large pupils (provides better vision underwater)
• claws
• pointy, vaguely finlike ears
• natural human hair colors and skin tones, with exceptions for slightly stylized colors (i.e. blue-black hair)
• no nipples and no naval

Pod structure:

• Leader
• Second-in-command
• Hunters, fighters, medics, and caretakers
• Misc roles
• Children and elderly