Homebrew Fish-Man Species Details

Fish-men are more fish-like than merfolk, usually looking like a combination between a man and a fish or other aquatic creature, such as an octopus, manta ray, or sawshark; however, they still have legs. They also have gills between their shoulders and necks, sometimes covered by their clothing, as well as often having webbed hands. Depending on species, they may have multiple limbs (mainly extra arms).

Size may also differ greatly between individuals, as Arlong was much taller than any of his crew members, but was small compared to Fisher Tiger, while Wadatsumi is even bigger than an ancient giant like Oars.

For fish-men pirates in pirate crews that are primarily fish-man based, (Sun Pirates, Arlong Pirates, and New Fish-Man Pirates) it appears customary to have that crew's jolly roger tattooed somewhere on the person's body, showing allegiance to a crew.

Biology

Fish-men have gills near their necks, which only work when they are in water. On land, they can breathe with their lungs like humans do. However, their gills cannot breathe in air, like a normal fish cannot breathe in air through their gills. 

Even though fish-men are part fish (or at least closer to fish biologically than human) and have been considered such by prejudiced humans in the past, they are still mammals and give birth to live young. Fish-men are also able to modulate the sounds that they make enabling them to speak in the same language as humans, yet at least one fish-man, Jinbe, has the ability to talk to other animals such as whales showing that a fish-man's larynx appears to be far more adaptable and capable of more than a human's. There are many merfolk who bear physical traits normally unique to fish-men, like Den's webbed hands and Shyarly's fangs. Furthermore, fish-men can sometimes demonstrate powers usually unique to merfolk, such as Jinbe's ability to communicate with whale sharks.

Do you know the difference between you and I? It's our species! This is the strength of the fish-men species from birth. Heaven gave us the power to separate us from you. So we are different! Humans are lower and weaker since the day they were born.

— Arlong boasting to Luffy about the strength of the fish-men race

Fish-Man Traits

Your Fish-Man character has the following racial traits.

Ability Score Increase

Your Strength increases by 3 and your Constitution increases by 1.

Age

Fish-Men reach maturity around age 15 and live up to an average of 100 years.

Size

Fish-Men are slightly taller than humans, averaging about 6-10 ft. tall. Your size is Medium.

Speed

Your base walking speed is 30 feet, and you have a swimming speed of 30 feet.

Amphibious

You can breathe air and water.

Darkvision

You can see in dim light within 60 feet of you as if it were bright light and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

Emissary of the Sea

Aquatic beasts have an extraordinary affinity with your people. You can communicate simple ideas with beasts that can breathe water. They can understand the meaning of your words, though you have no special ability to understand them in return.

Guardians of the Depths

Adapted to even the most extreme ocean depths, you have resistance to cold damage.