Not everyone would get excited about being gifted a 170-year-old fish, but when you are an ichthyologist it feels like Christmas.

John Pogonoski is one such fish scientist who manages a collection of 160,000 fish specimens, which includes the very old skate.

It was caught in Denmark in the 1850s and donated to the Australian National Fish Collection in 2002.

The collection, managed by the CSIRO, opened in Hobart in 1984, and holds most of its specimens in ethanol-filled jars and tubs.

"I guess it's a bit like a library of fish … instead of a library of books," Mr Pogonoski said.

He said that in the 13 years he had been working with the collection, it had become much more than a job.

"You wander around the collection and you get to know where everything is," he said.

"Some groups get looked at a lot more than others and you're always finding something new and interesting."

CSIRO specimens make up its fish library ( ABC News: Carla Howarth )

'Like stamp collecting'

A freshwater gudgeon collected from the Hunter River in New South Wales in 1901 is the oldest Australian specimen in the collection.

In one ethanol-filled tub, there are a number of sharks' heads, including a white shark that was accidentally caught by a fisher in Stanley in Tasmania's north-west five years ago.

This white shark was added to the collection after being accidentally caught. ( ABC News: Carla Howarth )

Mr Pogonoski said they often need to chop up the fish so they can fit them into the tub.

"We don't have the capacity to keep massive animals that are over 2 or 3 metres in length, so we have to make decisions on those animals about what's the most important thing to keep," he said.

"So often it's the head, the jaws, sometimes the fins, so they can be compared to fins that might be taken in the shark-fin trade."

The specimens come from a number of places, like CSIRO research vessels, Asian fish markets, donations from commercial land recreational fishers, and even other fish collections.

A specimen of a goblin shark. ( ABC News: Caral Howarth )

Mr Pogonoski said they swapped specimens with other fish collections, just like "stamp collecting".

"For every specimen we bring in we have to decide on its value and whether we keep it or not. We don't have unlimited space," he said.

"We also get genetic samples before we put them in preservative so that we have DNA for purposes that we haven't yet discovered that will no doubt appear as the 21st century moves on."

CSIRO's John Pogonski and Helen O'Neill love their unique jobs. ( ABC News: Carla Howarth )

Research Assistant Helen O'Neill said there were a number of reasons to have an archive of fish.

"We undertake active research … from describing new species, taking genetic samples and identifying fish that way and also doing some environmental DNA work," she said.

"Another important reason for the collection is to study evolutionary history and how things have evolved such as the the saw fish and saw sharks, how they've both evolved these long rostrums with the teeth on."

Possibly extinct handfish among specimens

The collection has specimens of the three types of handfish found in Tasmanian waters, one of which could be extinct.

The ziebell's handfish specimen was collected in 1986, north of Fortescue Bay on the Tasman Peninsula.

"The ziebell's handfish hasn't been seen since 2007, that was the last time there was a confirmed ID of this species in the wild," she said.

The scientists take genetic samples to preserve for future use. ( ABC News: Carla Howarth )

Ms O'Neill said overall, her job was fascinating.

"I do like some of the more unusual looking sharks, the hammer heads, the way that they're so broad and the eyes on the back of their head," she said.

"There's huge diversity in all the different species, the different evolutionary traits that have been developed to cope with different environments and overcome different challenges they've experienced."

"Whether they have light organs that attract prey or huge teeth, I find that really interesting, how they've evolved and all these different strategies nature has come up with."