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The largest predatory animal on earth is the sperm whale. They dive more than 1000 meters deep hunting for food. These animals are named after their huge heads, which make up nearly a third of the total length of their bodies. They have the largest, heaviest brain of any species known to have lived on Earth, weighing up to 9.5 kilos. Scuba diving with sperm whales is a beautiful sight you would never forget where you can admire their furrowed skin and marble-like coloration.

Charismatic, curious, cute, and smart are all reasons the bottlenose dolphin is the most well-known of the dolphins. The upward curvature of their mouths gives them the appearance of always smiling and their extreme intelligence makes them the easiest cetacean to train. Combine this with their friendly looks and it’s no wonder why they are the stars of most aquarium shows and many Hollywood movies. Not only do people have access to viewing them at most aquariums around the world, they are also the most common dolphin found in the wild, living in temperate, sub-tropical, and tropical waters all around the globe in almost every type of habitat.

The round, sweet eyes of a seal don’t only make these acrobatic mammals one of the cutest creatures in the sea but have a highly functional purpose as well. Seals have excellent underwater vision, especially in dark and murky waters. Being deep divers, sometimes reaching depths of up to 100 meters, having this increased ability to see in low light conditions is not only beneficial, but necessary to survive. Their bodies have also adapted to allow for these deeper, longer dives better than other marine mammals. Seal’s blood contains special properties allowing them to absorb more oxygen than other marine mammals, therefore allowing them to do these deep, long dives with ease.

The green sea turtle, also known as the green, black, or Pacific green turtle, is one of the largest species of sea turtles and has a wide population distribution throughout the world’s tropical and subtropical seas. There are two distinct populations in the Pacific and Atlantic Oceans, but they can be found throughout the Indian Ocean as well. They are unique in that they are the only species that are strict herbivores as adults, feeding mostly on algae, seagrass, and seaweed.

There are nearly 130 different species of marine butterflyfish all living in the tropical waters of the Atlantic, Pacific, and Indian Oceans. These beautiful, small fish are known for swimming in monogamous pairs but can sometimes be seen in large schools. Like their larger cousin, the angelfish, they are a favorite sighting for scuba divers and snorkelers due to their beautiful, bright coloration and striking patterns. Another distinguishing characteristic is the eyespots many species have on their flanks to trick predators, similar to those found on butterfly’s wings.

Despite their protruding teeth, menacing grin, and aggressive predatory status, barracuda are actually completely passive towards divers and snorkelers, although passing by a large adult can still be intimidating to the most experienced scuba diver. They are found in tropical and temperate oceans throughout the world, preferring to cruise over coral reefs, seagrass beds, and near the surface of the water, never venturing very deep; therefore, they are commonly sighted while scuba diving.

The puffer fish is named after its ability to inflate itself like a ball in danger or stress. They pump water into a sac-like enlargement of their stomach, causing them to deform into a ball. This change in volume makes it almost impossible for predatory fish to swallow the puffer fish and it can even suffocate them. If this stress reaction is caused willfully by divers, puffer fish can sometimes inadvertently suck in breathing gas from divers, which leads to them being buoyant and floating helplessly on the surface. This usually ends fatally for the animal. They are rarely eaten by predatory fish, but dolphins have been observed to get intoxicated on these animals by chewing lightly on them, which causes the puffer fish to release small doses of the strong neurotoxin tetrodotoxin. This poison is fatal to humans and no antidote is known; ironically, however, in Japan puffer fish is considered a delicacy called fugu. However, people’s curiosity about this questionable delicacy leads to accidents every year.

Seahorse is the generalized name given to 45 of the smallest fish species in the Hippocampus genus. Their name is derived from the distinctive, horse-like shape of their head and neck. They spend most of their time anchored by their tails to coral and plants. Each of their eyes can move independently, giving them the ability to watch for predators and search for food simultaneously. These creatures are incredible, mysterious, intriguing animals. They are also very illusive so keep your eyes open and maybe you’ll be lucky enough to dive with seahorses.