Captivity in aquariums and zoos isn’t suitable for all animals. The complex diet and large environments some species need are difficult to replicate in captivity, leading to quick deaths in some animals. Here are 17 animals you won’t find in aquariums and zoos.
Saola

The saola, or Asian unicorn, was discovered in 1992 and is considered one of the world’s rarest mammals. The saola is considered critically endangered, and all efforts to keep them in captivity have lasted for short periods before they died within weeks.
Narwhal

Narwhals, toothed whales distinguished by their long tusks that can grow to 10 feet, can’t be found in aquariums. IFL Science explains that the two attempts to keep them in captivity in North America “ended in calamity and tragedy” after the whales quickly died.
African Wild Dog

This endangered animal is the largest wild canine in Africa, and disease outbreaks, habitat fragmentation, and human persecution threaten its small population. African wild dogs can be found in zoos, but conservation zones in their native habitat have proven more effective.
Blue Whale

The WWF explains that the blue whale “is the biggest animal on the planet, weighing up to 400,000 pounds (approximately 33 elephants) and reaching up to 98 feet in length.” Their enormous size makes it impossible to provide them with enough space in an aquarium.
Giant Squid

This squid species displays deep-sea gigantism and can grow up to 43 feet long. This gigantic size makes it difficult to house them in an aquarium, and finding live individuals is incredibly rare; most are found washed up on beaches.
Javan Rhino

This critically endangered animal is the most threatened rhino species. The WWF explains that “only around 70 individuals live in Ujung Kulon National Park in Java, Indonesia,” so they can’t be found in zoos.
Gobi Bear

No gobi bears are in zoos, and only around 40 individuals live in the Gobi Desert of Mongolia. Gobi bear hunting was banned in 1959, and today, conservation efforts to tag and feed them are underway at the Great Gobi Strictly Protected Area.
Sumatran Rhinoceros

This rare species is the smallest rhinoceros, with two horns and a reddish-brown coat. The rhinos are considered critically endangered by the IUCN, with just five substantial populations in the wild and an estimated population of under 80 mature individuals.
Greenland Shark

The Greenland shark is a poorly studied species, but it is known for its extremely slow growth rate and long lifespan, estimated at up to 500 years. Their huge size would make them difficult to manage in captivity, and their deep-water habitat would be challenging to recreate in aquariums.
Great White Shark

Efforts to keep great white sharks in captivity have been short-lived and unsuccessful. Science Alert explains that “it takes an insane amount of resources for the aquarium to pull,” and “the sharks die quickly outside of the oceans no matter what zookeepers do.” Aquariums can’t match the size of the waters that great white sharks are used to living in, so the stress of the enclosed environment often leads to their death.
Kākāpō

This large, flightless bird is endemic to New Zealand and is considered critically endangered by the IUCN. It is only allowed in captivity as a rescue bird and is managed by a breeding program in patrolled, pest-free reserves, so it can’t be found in zoos.
Giant Armadillo

Giant armadillos are rarely found in zoos, but Bioparque Los Ocarros in Colombia is known for keeping them. They are considered vulnerable to extinction, and their extensive daily burrowing needs are difficult to replicate in captivity.
Indri

This large lemur is only found in Madagascar, and no individual has survived for over a year in captivity. Its nuanced diet can’t be replicated in captivity, and it doesn’t reproduce when taken from the wild.
Vaquita

This critically endangered porpoise has been driven to the point of extinction by illegal totoaba fishing. The Porpoise Conservation Society says, “The totoaba, a large fish native to the Sea of Cortez, is entwined with the vaquita’s fate in a tangled web of illegal fishing, black-market demand, and a race against extinction.” Vaquita are caught in the nets, which has led to only around ten surviving individuals.
Iberian Lynx

Twenty years ago, the Iberian lynx was on the verge of extinction, but its populations have gradually recovered thanks to intensive conservation efforts focusing on habitat and prey restoration. Over the past decade, a few individuals have been kept at Jerez and Lisbon zoos.
Pygmy Three-toed Sloth

This sloth is endemic to Isla Escudo de Veraguas, a small island off Panama, and considered critically endangered. Only around 100 individuals are believed to live in the island’s red mangrove thickets.
Popa Langur

This recently discovered monkey species is considered critically endangered, with only 200 to 250 mature individuals. They are native to Mount Popa in Myanmar, a sacred pilgrimage site, and are believed to have once been widespread across the country.
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