This deep-dive special episode explores the extraordinary underwater world of Chester Zoo, featuring blind fish, rare amphibians and a frisky penguin

As the festive season approaches at Chester, the zoo's youngsters - from giraffes to monkeys - are about to have their first Christmas, and there are other newbies, too.

Keepers are curious when Margery the Malayan tapir is suddenly eating for two; a deadly virus is suspected of being the cause behind a female hyacinth macaw's untimely death, her partner James Bond must undergo total isolation.

A couple of giant otters welcome four pups and must learn the difficulties of parenthood; a Red River hog struggles to survive alongside her two sisters; zookeepers try to help a sickly Batagur turtle that has them concerned.

The zookeepers run into obstacles as they try to transport an Asiatic lion king Iblis and his kin to a new habitat; a fight breaks out in the vampire crab exhibit; an Andean bear suffers from a broken heart and a toothache.

Zookeepers work through trouble as they try to pair Chester's newest bongo couple; a trio of silver-eared mesia chicks must find new shelter when a major storm destroys their nest; a Malagasy giant rat must undergo surgery.

A violent fight breaks out when a new chimpanzee attempts to overtake the current matriarch; the Zookeepers excitedly await confirmation that two Chinese croc lizards are expecting; two pink pigeons struggle to raise their young.

A sickly orangutan named Sarkiei mus be quarantined away from her prized son; when a mother giraffe named Dagmar becomes too thin, the zookeepers consider separating her from her calf; a male giant otter pup refuses to eat.

Keepers are curious when Margery the Malayan tapir is suddenly eating for two; a deadly virus is suspected of being the cause behind a female hyacinth macaw's untimely death, her partner James Bond must undergo total isolation.

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Chester Zoo's alpha male lion is having a crisis of confidence. There's been a bloodbath among the vampire crabs. And affable Andean bear Bernie has been kicked out of the family paddock.

Newcomer Safi, a rare bongo antelope from the mountains of Kenya, is giving enthusiastic breeding partner Moti the runaround. Very soon the keepers realise why - it seems she may be about to give birth earlier than expected. Sunda gharial crocodiles Frank and Frankie need to have their blood tested - but taking a sample from one of the world's largest and most dangerous reptiles is easier said than done - and George the giant rat needs to have surgery after an X-ray pinpoints a huge lump of hard faeces in his stomach.

Vila the chimp makes a bid for the job of top female only to get hurt in a fight with rival Alice. And Chester Zoo's super-rare pink pigeons need to stop arguing and start mating.

Young rat snake Sen meets male Jakob, but will they mate or will Jakob eat Sen for dinner?. When Bornean Orangutan Sarkiei becomes sickly, keepers must separate her from prized son Tombol and Rothschild's giraffe Dagmar becomes dangerously thin, keepers must determine whether or not to part her from calf Mburo. The male giant otter pup is struggling to eat and walk.

When dik dik Kahri becomes a dad, his fight or flight instinct goes into overdrive. Meanwhile, the keepers face the dangerous task of replacing a broken window in the reticulated python habitat.

Spider monkey Kiara seems more interested in hanging out with the youngsters than looking after her baby. Baby capybara Henry enjoys having the attention of all the female capybaras.

Kendari the babirusa is pregnant, but otters Wallace and Annie keep throwing stones at her house. Next door, orangutan Willie is struggling to impress females Sarikei and Leia.

As the documentary series following life at Chester Zoo returns, on Chimpanzee Island the younger males test the pecking order. And there's a fish out of water at the aquarium. Deer couple Serena and Odin welcome their second doe.

Two of Chester Zoo's zebras are about to give birth. Meanwhile, lioness Kumari seems to be losing interest in her partner, Iblis. And two of warthog Magnum's children are becoming hard to control.

Sloth Tina has been giving her partner Rico a hard time, but the keepers have a plan to bring them closer together. And three-legged chameleon Tripod goes speed-dating.

A potentially deadly virus hits the elephant house. Will Chester's female zebras be interested in new stallion Mac? Plus: the bizarre world of the naked mole rat.

Penguin chick Munch fights for his life when there's disease in the colony. When young male tortoise Football muscles in on 71-year-old Bert's harem, the keepers bring in two Swedish female tortoises.

It is time for mouse deer Una to leave her parents and meet a mate of her own, but she is being shy around her future partner, Biani. Aardvark Koos gets romantic with his sister in this night-time special. Can underdog seahorse Seabiscuit grow the vital appendage he needs to attract a mate?

Sloths Tina and Rico aren't getting on, and she won't ever let him get close to her. But Tina starts to put on weight. Is she pregnant? Or just eating too much? Plus: lions and monkeys and frogs.

Flamingo mum Calypso loses interest in mothering her chick, Marley. Three of the zoo's rare onagers are pregnant at the same time. And a baby macaque gets picked on by some older females.