Are Cowfish Poisonous To Humans? (This Little Fish Packs A Big Punch)

There are many fish in the ocean that are deadly in one form or another. Many warn you that they pack a punch but some go about their day looking very innocent and beautiful like the Cowfish. But did you know this cute popular saltwater aquarium fish is poisonous to humans and deadly to other fish?

Are cowfish poisonous to humans? Some fish inflict a venomous sting that will kill other fish when they feel threatened and some have the ability to release a toxin into the water which can kill fish. Humans will not be in any danger unless they eat an uncooked cowfish. This could result in being poisoned from a different type of toxin, palytoxin.

The cowfish is deadly thanks to a unique poison that is only found in this species and some sea cucumbers. It is one of the most deadly poisons found in the ocean and is only used in self-defense.

Longhorn cowfish poison

Why Are Cowfish Poisonous?

Like all sea creatures, Cowfish and Boxfish are hunted by larger sea predators. Over thousands of years, most fish have developed some form of defense against being eaten or attacked.

Large schools as a defense

Some fish swim in huge schools which makes it harder for larger fish to catch them. Anchoveta springs to mind when I think of a large group of fish that school for defense.

Body shape as a form of defense

Others use their body as a form of defense, often having sharp fins or spines that can inject venom into any fish that tries to eat them. The lionfish not only uses its body shape as a defense but also has the ability to inject a strong toxin via their venomous fin spines.


Some species are simply violent and aggressive like sharks and freshwater fish like the Piranha are the first ones that I thought of. Moray eels are another fish that uses sharp teeth and aggressive behaviors to scare off predators.

longhorn cowfish
The longhorn cowfish is packed with defense mechanisms.

What Defense Do Cowfish Have?

Cowfish have developed three main types of defense.

  1. Their horns have grown longer over thousands of years to prevent other fish from swallowing them whole. This is fine as a defense for smaller fish. Not so good against larger species. Hence they have another form of defense.
  2. Their body contains a poison called Palytoxin, one of the most toxic non-protein poisons known to man. However, this is not released into the water and will only affect fish or humans if they eat a cowfish.
  3. The strangest and most often poison that a cowfish can produce which is the one that sometimes wipes out whole aquariums is Pahutoxin. This poison is held within the skin cells of this species of fish. They release this into the water when they feel threatened or become stressed. This poison has the ability to kill every fish in your aquarium.

7 Little known facts about cowfish here!

So, Are Cowfish Poisonous To Humans?

There have been some reports of human dying after eating cowfish. How true this is, I’m not sure but I am not 100% convinced.

Palytoxin is without a doubt one of the most toxic poisons know to man which has the potenial to kill. But is there enough poison in a cowfish if eaten to kill a human? I doubt it but I’m no toxicologist (Someone who studies Poisons).

In some parts of the Pacific they are eaten and considered a delicacy. They are roasted and eaten cooked. Many be the reports of people getting sick or even dying was due to the cowfish not being completely cooked through.

I know I would rather see them swimming in the pacific or in a large aquarium than being roasted and eaten.

Read our complete care guide for cowfish here!

cowfish being eaten in sushi bars
Cowfish is eaten in the far east in sushi bars and restaurants
Image credits here

Conclusion: Are cowfish Poisonous To Humans?

The answer has to be yes, but have humans died from eating cowfish? I don’t think they have. If anyone has eaten a cowfish and died they must have had underlying conditions which caused their death.

As aquarists we should, however, ensure they don’t become stressed as they will release their skin toxin which is like a gel that is released from the skin into the aquarium which definitely can and often does kill the contents of an aquarium. If left to enjoy their aquarium your cowfish will live a long and happy life and so too (hopefully) will your other fish.