Coral reefs are like the big cities that never sleep. Every creature is part of a delicate balance where adaptation is the key of survival. Every day, fish must defend themselves from a wide range of predators and therefore have developed incredible strategies. Some camouflage, others use sharp spines, or have poisonous skin and some species even mimic others. Here, the fight for life never stops. Understanding the defence mechanisms of marine life is important, because it has implications for how we interact, or don’t, with those organisms. Some creatures are poisonous and others are venomous, but what exactly does it mean?

While these terms both involve toxins, it is the way the toxins are delivered that makes the difference. Venom is injected. Poison is ingested. Venomous animals inject their toxins actively, through a bite or sting, the delivery is intentional and used often for hunting or self-defence; poisonous animals are harmful if eaten or touched, the toxin is ingested or absorbed through the skin.

Boxfish
Boxfish are members of the family Ostraciidae, with 23 different species. Colorful fish with a box-shaped body, tiny fins and very shy personality, boxfish possess also a powerul chemical defence mechanism. When subjected to acute stress (like chased, harassed or handled) they can secrete a potent poison called Ostracitoxin from their skin. Ostracitoxin is dangerous for other marine life in the immediate area, causing damage to their gills which will make them suffocate. However the poison will quickly dilute in the water causing no harm to humans.

A baby box fish

Pufferfish
With their funny appearance, pufferfish are clumsy swimmers but also one of the most toxic animals in the ocean. Many species carry Tetrodotoxin (TTX), a powerful neurotoxin found in their liver, skin and sometimes other organs. This substance is incredibly dangerous, if ingested even a small amount can be deadly to humans. As absorption of TTX is not through the skin, it poses no threats to divers observing these curious animals. They also have another way to defend themselves, if threatened they can self-inflate their body like a balloon (it is very painful for them), to three times their normal size.

Map puffer fish

Stonefish

They are real masters of camouflage, perfectly blending in on the reef to look like a rock, these bottom-dwellers possess one of the most painful defece mechanisms. Stonefish have sharp dorsal spines connected to venom glands, and if stepped or accidental touched they can deliver a painful sting: the venom can cause intense swelling, muscle pain, but if treated quickly it is not fatal or dangerous. Despite their reputation, Stonefish are not aggressive, in fact they prefere to stay still and hidden on the reef. The key is awareness: do not touch anything underwater, especially on reef flats or sandy bottoms.

Stone fish

Stingrays

Rays are some of the biggest and least known fish in the ocean. On the planet there are over 630 species of rays and 220 of them are stingrays. Creatures with calm and elegant movements. Stingrays play also a crucial role in maintaining healthy marine ecosystems. As bottom-dwellers, they feed on crustaceans, mollusks and small fish, helping to aerate the seabed and control populations of benthic invertebrates. Stingrays have a sharp, venomous barb on their tail. Fatalities are extremely rare, but their sting can cause intense pain and infection. But don’t worry, Stingrays are really peaceful animals and they use their sting solely for self-defense and only if threatened.

A Stingray