Would you eat an animal if you knew it was as old as the U.S. Constitution?
Scientists in New Zealand have aged a fish called an orange roughy at between 230 and 245 years old, making it one of the longest-lived fin-fish on record.
The ancient fish was born in the late 1700s — and then caught in 2015 by a New Zealand commercial fishing boat on the Louisville Ridge, a chain of seamounts in the South Pacific around 930 miles east of the mainland.
The spiny, scarlet creature was hauled in by a trawl net from its deep, dark home more than 3,000 feet below the surface, along with many hundreds of its schoolmates. But before it was sold and eaten, New Zealand government observers on board the ship extracted samples from inside the creature’s head to determine its age.
Orange roughy — known as “slimehead” before a marketing makeover in the 1970s — are mainly caught off the coast of New Zealand and Australia, then sold abroad, mainly to the U.S.
Whole Foods, Trader Joes and some other retailers refuse to stock the species, citing sustainability concerns and the environmental impacts of bottom trawling. For researchers, the species’ great age highlights the need for a precautionary approach to fisheries management.
Scientists age orange roughy using otoliths — or “ear stones” — which work like our own inner ear, helping fish balance and orient. Each one is a hard crystal of calcium carbonate, or limestone, the same stuff stalagmites are made of. Like stalagmites, they build up layers each year a fish is alive. Scientists can use those layers to age the fish.
“When you cut the otolith in half you see darkish and lightish bands similar to tree rings,” says Peter Horn, a fish ageing expert at New Zealand’s National Institute of Water and Atmospheric Research.
This year, Horn examined the otolith samples as part of a recently published government report into how the age of orange roughy caught at Louisville Ridge changed between 1995, shortly after fishing started in the area, and 2015. (He found that after two decades, there were fewer large, old males, and the average age was 8 years lower.)
A thin section through the middle of each otolith was mounted on a slide. When Horn picked up one particular specimen, he could immediately see the animal was old.
“You hold the slide up and think, gosh, it looks like we’ve sectioned a brick here,” he says. The oldest orange roughy previously found around New Zealand was 180, though older specimens have been discovered elsewhere. So, to be sure, Horn did five separate counts, coming up with a variety of ages between 230 and 245.
Knowing a fish population’s age distribution is important for fisheries management, but studying otoliths isn’t quite as easy as counting tree rings, says Kyne Krusic-Golub. The Australian fish ageing expert reckons he’s aged around 5,000 orange roughy over his career — including two from the Cascade Seamount off Tasmania that were around 250 years old.
Not much changes in the deep ocean between winter and summer, which means the annual markings are subtle. Scientists now have the technique down to an art — but that wasn’t always the case. And the history of orange roughy in New Zealand is a cautionary tale.
When the orange roughy fishery began in the late 1970s, scientists thought the species lived to just 30 years old. Two decades later, it became clear that they mature only at around 30, don’t breed every year, and grow incredibly slowly.
By then, many stocks had collapsed and three of the eight New Zealand orange roughy fisheries had been closed (though they have now recovered, and some have been certified sustainable by the Marine Stewardship Council.)
Scientists have since developed a verified ageing protocol for orange roughy otoliths. One way to check their accuracy utilizes former French nuclear weapon tests at Mururoa Atoll in the southern Pacific Ocean. The timing of radioactive isotopes from the bombs can be tied to individual otolith rings, giving a precise age.
The method shows that orange roughy live to a record-breaking age for a commercial fish. For most others, 60 or 70 is old.
Still, Krusic-Golub says, other ancient fish may be waiting to be found.
“There might be some ‘trash fish’ that live with the orange roughy…. that possibly could get that old as well, they just haven’t been exploited and measured because they’re not a food fish,” he says.
Apart from orange roughy, there are a few other marine animals that have been found to live past 200 years — bowhead whales, Greenland sharks, and an ocean quahog clam called Ming that made it to 507 — but these are less likely to appear on restaurant menus, Horn observes.
“I do have to admit that yes, when I started to get some fish over 200 (years old), I was thinking, gosh, this thing had been tootling around in the ocean for two centuries, and suddenly it has a bad day and ends up on some bastard’s dinner plate,” he says.
“You think — that really is sad.”