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

A look back at the most extraordinary births caught on camera at Chester Zoo., including a pregnant elephant and a wasp seeking a cockroach for a mate to paralyze with venom.

Some of Chester Zoo's animals are happily together forever, including penguins Rudd and Spike, and sloths Tina and Rico, who spend up to 18 hours a day fast asleep.

A look back at some of Chester Zoo's expert escapologists, from Sumatran orangutans to blue-throated macaws and an Andean bear cub on the adventure of a lifetime.

Pedro the giant anteater falls ill and faces a major operation. Chester Zoo's rare bald ibises produce a batch of new chicks. And a rhino couple are reunited after four years apart.

A look at some memorable new families, including new arrivals for a rare breed of horse, a couple of squabbling red pandas, and a breeding phenomenon in Chester Zoo's aquarium

A look at some memorable moments of animals behaving badly at Chester Zoo. The chimps are up to no good. Two noisy otters are in for a shock when they're re-housed alongside the orangutans.

More memorable moments from Chester Zoo as baby elephant Indali receives cutting-edge treatment for a deadly virus. Caiman lizard Gary keeps diving into an empty pool. Plus: camels, and clownfish.

More memorable moments from Chester Zoo as baby elephant Indali receives cutting-edge treatment for a deadly virus. Caiman lizard Gary keeps diving into an empty pool. Plus: camels, and clownfish.

Compilation of highlights from previous episodes. An orangutan has to be separated from his mother for the first time when she undergoes a CT scan to check for a life-threatening infection. The zoo's cardinal fish undergo a breeding programme, but one struggles to protect his offspring from his circling, cannibalistic neighbours.

Young orangutan Indah decides to open all of her family's Christmas stockings. There's a Christmas baby in the tapir house. Ten brave keepers have to catch reticulated python Bali for a health check.