People are being urged to buy and eat unfamiliar species of fish in the interests of sustainability.

Key points: Bastard trumpeter, blue warehou and other popular species are in decline

Bastard trumpeter, blue warehou and other popular species are in decline People are being urged to try lesser known species of fish

People are being urged to try lesser known species of fish Unpopular fish species often have larger stocks and can be fished more sustainably

Caleb Gardner, director of Sustainable Marine Research, at the Institute of Marine and Antarctic Studies, said the range of seafood people eat is getting smaller, while the demand for popular species is growing.

"We've got increasing supply that's coming through aquaculture and we've got increasing trade from overseas," he said.

"We've also got a smaller range of seafood that people seem to be buying from the wild catch … and fewer and fewer of the species that can be caught in local waters.

Caleb Gardner says the science shows we should be eating a wider variety of fish. ( ABC News: Cameron Atkins )

"We're becoming fussier and that's good in one way, but it also means some great seafood is dropping off the list and we could be eating those."

Old favourites 'dropping off the list'

It is a trend Professor Gardner — one of the nation's top fisheries scientists — knows all too well.

"Back when I was a kid you'd go into a fish and chip shop and there would be 30 species of fish on the wall that you would pick from," he said.

"Today its usually just one species … and it's whether it's battered, crumbed, grilled, or Cajun because the choice has just narrowed.

The variety of fish available in shops has declined. ( ABC News: Cameron Atkins )

"We've got something like 500 species around south-eastern Australia that we could eat but if you ask people what species they know we can eat they'd probably struggle after a handful like blue eye, flathead, garfish and snapper."

The fisheries scientist wanted people to try fish like sardines and mackerel which are found off the coasts of the south-eastern Australia.

"We've got large quotas, those quotas are barely being used, they're fantastic eating fish which are eaten in other parts of the world but we are not using them," said Professor Gardner.

Tricky cooking, strange names and reputation to blame

Third generation Hobart fishmonger Wilson Mure said he supplies a diverse range of local fish in his shop, but that doesn't mean consumers always buy it.

"The demand seems to be narrowing towards the more convenient species," he said.

Hobart fishmonger Wilson Mure, says consumers are less "adventurous". ( ABC News: Cameron Atkins )

"The blue eye and the salmon especially, don't have many bones and have a very long shelf life compared to some of the oilier fish, so people can take it home and don't have to cook it straight away.

"People are less adventurous and once they know a fish is so versatile and easy to use, they're not going to want to stray away and try something else just in case.

"But we try to push [different species] as much as possible — because they're just as delicious."

Consumer demand is reducing the variety of fish on sale, says Wilson Mure. ( ABC News: Cameron Atkins )

Professor Gardener agreed.

"The species we're not using tend to be trickier to cook or they sometimes have strange names or just have a reputation that maybe they're not the most premium species," he said.

"But they can be a whole lot cheaper and really heathy and they're a great thing to eat for the ecosystem because we can harvest them sustainably.

"Species like flounder or barracuda, Australian salmon, long fin pike, short fin pike, leather jackets, gurnards, there's a whole bunch of species out there that we're just eating fewer and fewer of so that makes it difficult for producers to put it into the market."

Sydney Fish Market's Alex Stollznow holding an Albacore Tuna, a fish he considers under utilised. ( Supplied: Sydney Fish Market )

Alex Stollznow from the Sydney Fish Market has used social media to promote less popular fish.

"One we posted recently was the flutemouth fish, it is long and shaped like a pipe … and it's got this bizarre mouth, most people walk past it in the shop," he said.

He said customers sometimes judge their fish a little hastily by appearance, but he urges people to give strange looking fish a go.

"The flutemouth fish for example, looks bizarre but it's a really easy fish to cook," he said.

"If people aren't buying, the price stays low but when people see it cheap, they don't want to buy it," said Mr Stollznow.

Professor Gardner said some fishers aren't catching their quota, citing reasons like low demand, low prices, high labour costs, competition from aquaculture and even public opposition to some commercial fisheries.

"Higher demand and higher prices would tip the pendulum towards these unused stocks," he said.

Minor species great for everyday eating

Eloise Emmett, a chef and seafood advocate, is so keen to get people to cook all kinds of seafood she has written a cook book focussing on minor species.

However she said often strange fish, whether they are bycatch or just catch, they need to be turned around and sold quickly, the fresher the better.

Lesser known fish species are ideal for strongly spiced dishes said chef Eloise Emmett. ( Supplied: Eloise Emmett )

Her family is in the fishing business, she first started coming up with new recipes for minor species out of frustration.

"A load of hard to sell species that people don't often see would end up going to the fish and chip shop, that's good, but they would be good in my opinion in restaurants but also in the home kitchen as well," she said.

She recommended using minor species for weeknight meals like fish pie or fish burgers.

"If you're going to make a Moroccan stew for example, there's no point using a delicate, expensive fish like flathead, blue eye or salmon because you're almost going to cover up the flavour with the spices, so I would recommend using one of the under-utilised species in a recipe like that," she said.

She said people should increase their fish buying and start trying to cook the cheaper fish during the week and leave the expensive fashionable fish for weekend dinner parties.

Professor Gardner asked people to also do their homework and trust the science about Australia's fisheries.

"We do have all these large quotas allocated for fish and they're not just plucked out of the air they're based on scientific analysis," he said.

Some parts of the controversial orange roughy or deep sea perch fishery has recovered, but that fishery still has a bad reputation in the marketplace.

"Far more orange roughy was taken than should have been … those problems were 30 years ago, orange roughy stocks have recovered in a lot of areas, there is a 500 tonne quota available and zero of it was caught."