The age of aquarium

There’s a place right at the bottom of The Deep known as “the tunnel”, a glass passageway across an authentic reproduction of an ocean floor. Unless you are a deep sea diver, being there is probably one of the most thrilling experiences you’ll ever have.

It’s at this point where you get a sense of almost leaving dry land behind and becoming enveloped by a greenish-blue world of reefs and seaweed. And if you stand there long enough you will begin to feel as though you have gone native and joined a swirling fraternity of big fish – sharks and stingrays, shoals of jacks, and a couple of fearsome green swordfish.

It’s a constantly changing scene, and one that has been enjoyed by over four million people since the aquarium – or “submarium” as The Deep prefers to be known – was first opened in 2002.

The journey starts in a lift to the third floor of a building which looks like a ship’s bow has been left stranded at the confluence of the River Hull and Humber estuary. You then proceed down a series of gently sloping ramps ingeniously wrapped around the 10-metre-deep main tank.

But in the lift there is a button without a number, and if pressed the lift stops on the second floor. This is a place which the public never get to see. It’s where the backroom operation of looking after thousands of fish and reptiles goes on seven days a week.

Here, curator Katy Duke and her 14 staff start the day by planning and preparing meals for 3,500 fish, reptiles and invertebrates, a task made hugely complicated by the fact that many of them have special dietary needs and their appetites vary with each season. Every week they get through three family shopping trollies worth of fish.

“All of the fish is human-grade,” Katy says, “and sustainably sourced by our supplier at Grimsby. So it’s things like line-caught mackerel, it’s a variety of whiting and squid and freshwater fishes, plus krills and plankton-type food. Basically, we work on the idea that the more diverse diet you can give them the more natural it is, and also the more nutritional.”

The food is prepared in pots for individual tanks, and while some is fed directly into the water much of the food is supplied by a variety of slow-release methods. For instance, they use something called reef gel, a kind of putty made up of different types of plankton and algae, which is formed into plasticine-like balls and pushed into rocks and crevices by divers in the main tank.

Some species of fish, especially those from rivers and freshwater lagoons, require a vegetarian diet and are fed fried algae which has been stuffed into the small net-like vessels normally used for detergent tablets in washing machines.

Walnuts and Brazil nuts are also put in the water for the strong-jawed pacu from the Amazon. Each week other livestock here eat their way through several shopping baskets of lettuce, tomatoes, apples and bananas. The total food bill is £44,000 a year.

It is on this floor that seawater is manufactured. Taking water from the tidal and extremely muddy Humber was never going to be an option, so the tanks are constantly refreshed with water that contains a synthetic mix of salts to match conditions found in the sea. Three tonnes of salt are used each week to turn filtered tapwater into ocean water.

Each tank is monitored 24 hours a day to ensure the correct salinity, temperature and other factors, and preset alarms are triggered if there’s just one adjustment suggesting that something has gone wrong.

Katy says: “We call our filtration system ‘life support’, because it really is that important. It’s not just a matter of keeping the water clean with filters, the water has to be kept moving and oxygenated. If you’ve got the water chemistry right, then I think the fish health is pretty easy.”

There are tanks for breeding fish and for exchange with other large aquariums. The most spectacular tanks – it’s a shame they’re not on public view – are devoted to the production of thousands of jellyfish. Starting life as tiny polyps, they become a soup of small translucent umbrellas and gradually turn into the familiar jellyfish shape, at which point they are transferred to the public viewing tanks.

There are also quarantine tanks for fish that show any sign of illness. Usually, they can be returned to their individual tank after a few weeks but sometimes they require specialist treatment.

The Deep has on 24-hour call a specialist fish vet, Marc Geech, who is based in Oxford. Only once has he had to make the emergency four-hour drive to Hull, to attend to a Wobbegong Shark that had been bitten by another fish. Mostly, his visits are for inspections or routine surgery. He once used a mobile MRI unit in the car park to scan some of the sharks’ spines.

Several of the fish are endangered, reinforcing the value of the work that’s done there. There are around 25 potosi pupfish from South America, which are now extinct in the wild. The green swordfish are now so rare they can no longer be collected from the wild and put on public display, and Katy and her team feel a real responsibility towards them. They haven’t yet reached adulthood, and there are hopes that one day they will breed.

It’s from the second floor for that numerous international research projects are coordinated, ranging from studies off South Africa of the great white shark - the shark that terrorised beaches in the film Jaws – to studying sea cucumbers in the Red Sea.

Says Katy: “I see The Deep as a shop window that shows the beauty of what’s in the oceans and rivers, because not everyone has the luck to go diving in tropical locations to see it for themselves.

“It’s also a way for us to highlight some species that are threatened and need support. All types of wildlife it’s easiest for fish to be out of sight and out of mind, and so I think it’s our main role to bring these species to the public’s attention and to show the diverse amount of life that’s down there.

“History has shown us that if we don’t value our wildlife then it disappears. If we don’t look after the ecosystem of our oceans or rivers, then I think the entire planet will eventually be up the swanny.”

The Deep, Tower Street, Hull, HU1 4DP www.thedeep.co.uk

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World-wide work on conserving the seas

The Deep is a unique scientific centre as well as a tourist attraction. It has close links with Hull University’s department of Biological Sciences.

It is involved in conservation projects around the globe and is the only aquarium in the world working alongside Equipe Cousteau on a major project to protect marine life in the Red Sea threatened by unregulated shark fishing.

The Deep is helping Cousteau electronically to tag manta rays to monitor their movements. The harmless tags collect data including sea temperature and the depths at which the animals are swimming and transmit this to monitoring devices on the ocean floor. These will eventually be part of a global network to enable scientists to draw up a sustainable management plan for shark and ray populations. The Deep has also agreed to assist the Sudanese government to set up a small aquarium.

In Puerto Rico it is working on coral conservation with SECORE (Sexual Coral Reproduction). They collected spawn from the threatened Elkhorn coral which is now growing at The Deep.

Staff from the Deep collected samples of Lophelia pertusa from BP oil rig legs in the North Sea. This has helped to increase our knowledge of this recently discovered reef-building coral.