Two men are set to face court in Darwin after allegedly being found in possession of black jewfish swim bladders.

Key points: NT Water Police say there is a roaring, illegal trade in black jewfish bladders, which are highly sought after in parts of Asia

NT Water Police say there is a roaring, illegal trade in black jewfish bladders, which are highly sought after in parts of Asia Two men allegedly caught with bladders in their possession could face heavy fines if they are found guilty

Two men allegedly caught with bladders in their possession could face heavy fines if they are found guilty Industry groups and police are worried that overfishing could seriously damage the NT's fisheries

Under the Northern Territory's new fisheries regulations, swim bladders must not be removed from fish on the water unless they are disposed of immediately.

The swim bladder, or airbag, is an organ in the fish which regulates its buoyancy, and in recent years there has been a growing black market trade for them, with the bags considered a delicacy and an aphrodisiac in countries such as China.

"There is an illegal airbag market where the airbags are trading at around $1,000 per kilogram," NT Water Police Senior Constable Sean Stanley said.

"It roughly equates to around three airbags per kilogram, so it is a fairly lucrative trade at the moment.

"Our information tells us that they go to Sydney, and from there they are exported to China and South East Asia where they are used in soups, and also used as an aphrodisiac."

Senior Constable Stanley said the illegal trade had become his units' "number one enforcement issue".

Black jewfish swim bladders are considered a delicacy and an aphrodisiac in China. ( ABC News: Tom Maddocks )

Black market crackdown

The two men, aged 29 and 31, were apprehended during an enforcement patrol of the Charles Point area near Darwin.

The case is the first of its kind in the NT since fisheries regulations were amended last year, and the pair face maximum fines of up to $6,200.

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Senior Constable Stanley said black jewfish had been almost wiped out in some locations overseas and the species was at risk of being overfished in the NT.

"There is an area in the Gulf of Mexico which was targeted by illegal poachers in relation to these airbags, and now you can't catch a jewfish there," he said.

"What we are seeing is people are now targeting the northern waters of Australia — that includes Western Australia, Northern Territory and Queensland — and there is a huge market for air bladders here.

"We need to protect our fish stocks here, especially black jewfish, because I believe we have the best fishing in the world."

The black market for swim bladders has put populations of black jewfish under pressure. ( Supplied: NT Seafood Council )

NT Seafood Council CEO Katherine Winchester said the Water Police crackdown and promise to adopt a "zero tolerance" approach to the offence would hopefully curb the illegal trade.

"As black jewfish are an at risk species it is critical to ensure the right balance of regulation and enforcement resources are in place," Ms Winchester said.

"I believe the Northern Territory has possibly the only sustainable black jewfish fishery in the world, and we must ensure the risks of illegal targeting of bladders is being addressed to ensure a healthy fishery into the future."

"We encourage people to report any suspicious or suspected illegal activity regarding swim bladders, either directly to the FishWatch hotline (1800 891 136) or via the NT Fishing Mate app."