10 Dec 2015

Lampreys aka 'vampire fish'

From Our Changing World, 9:06 pm on 10 December 2015
Lamprey hanging off Cindy Baker's arm

Freshwater scientist Cindy Baker demonstrates how a lamprey can latch itself onto an arm, just as it does with fish and whales at sea, using its teeth and sucker-like mouth. The lamprey is a strong climber and capable of holding its own weight and scaling vertical waterfalls. Photo: RNZ / Alison Ballance

The lamprey twists and writhes as NIWA freshwater scientist Cindy Baker holds its mouth next to the soft skin of her forearm. Then it latches on, using hundreds of small teeth as well as the fleshy sucker that surrounds its small circular mouth. Once it has a good grip Cindy lets go and the eel-like fish just dangles, taking all its own body weight.

Lampreys – or vampire fish as they’re sometimes called – have perfected the art of latching onto large animals at sea, such as fish and whales, and using their sharp teeth to rasp into the flesh to suck out a feed of blood. Cindy doesn't let this particular lamprey linger on her arm for long, before she grabs hold of it firmly and pulls it off with a sucking sound.

But the lamprey has already left its mark: a neat circle of puncture wounds already oozing a little blood. It’s a striking demonstration of how strong and agile New Zealand lampreys can be, as well as how efficient their unusual parasitic feeding style is, and Cindy says they put this to good use when they are migrating.

“They’re amazingly good at jumping out of containers. They have a large sucker mouth that they use to help themselves migrate and they can scale vertical walls. As long as they have a wet surface they’re very adept at climbing up waterfalls and around obstacles in the water.”

Now, in case this sounds like a scary case of ‘coming to a river near you’, we should reassure you and note that this is NOT typical behaviour of a lamprey in freshwater. You will not be attacked by an adult lamprey in a New Zealand stream or river – so, with that reassurance in mind, keep on reading (or listening) to find out why.

Brown and blue life stages of a pouched lamprey

Juvenile and adult pouched lampreys are brown (like the adult pictured at left), while the migrating phase that moves from freshwater streams out to sea is a bright blue (right). Photo: RNZ / Alison Ballance & Shannan Crow / NIWA

While lampreys do have a strong mouth, what they don’t have is any jaws. Along with the fully marine hagfish, they are agnathans, the last two species in an ancient group of jawless animals. And as much as they look like eels they’re more closely related to sharks, skates and rays.

“Lampreys, we believe, have been around for more than 360 million years,” says Cindy. “Which if you think back to the time of the dinosaurs means lampreys were migrating upstream and passing them and carrying on their lifecycle. It’s only been since us humans have intervened that their populations are now starting to decline.”

Head of a lamprey

An adult lamprey using its circular mouth to suck onto a person's arm. The dent in the top of the head is a single nostril - the lamprey has an extremely sensitive sense of smell. Photo: RNZ / Alison Ballance

There is one species of lamprey in New Zealand, the pouched or wide-mouthed lamprey (Geotria australis), which is also found in Australia and South America. There are about 38 species found world-wide - and of these only 18 are parasitic in their feeding style. The most infamous lampreys are the sea lampreys that have become a pest in the Great Lakes system of North America. “You end up with multiple lampreys feeding on each fish in the Great Lakes, and it’s destroying their native fisheries,” says Cindy. This is also where the exaggerated tales of lampreys attacking people come from (and the web is full of such scary stories).

Lampreys are anadromous, which means they are born in freshwater, spend most of their life at sea, and then return to freshwater to spawn. Young lampreys spend about 3-4 years living in the stream or river where they were spawned, hiding amongst the gravel on the stream bottom. They live another three to four years at sea, parasitically feeding on large animals such as fish and whales, and then they return to a stream to spawn.

“Of all the lamprey species the New Zealand species is quite unique in terms of its freshwater breeding and life stage,” says Cindy “Most lamprey species live in freshwater for two to three months before maturing, breeding and dying. Pacific lampreys spend up to a year in freshwater, while our guys spend a year to a year and a half, and during that time they’re not feeding, which is really remarkable.”

During this long period of fasting and gonad development an adult lamprey shrinks to about 70% of the size it was when it returned from sea.

Lamprey bite

A lamprey bite on a person's arm - you can see an outer ring of teeth marks around a small wound, where the lamprey has used its rasping tongue to draw blood.The lamprey was hanging on using the sucker disc around its mouth. Photo: RNZ / Alison Ballance

Cindy describes lampreys as ‘mysterious’ and says that we know very little about their basic biology. The NIWA research programme she has been running has focused on locating where the lampreys are spawning, and in testing how lampreys use pheromones, which are chemical signals produced by juvenile and adult lampreys.

Individual lampreys were placed in a 5-metre long flume tank with two parallel channels (a bit like a lamprey lap-pool). Water ran through the flume tank and a control odour was dribbled into one channel and a very dilute pheromone dribbled into the other. The lamprey was then observed remotely to see if it had a preference; each animal was tagged with a small internal PIT tag which was detected by aerials in the flume tank. Lampreys have a single nostril on top of their head and an extremely sensitive sense of smell, and Cindy says the concentrations of pheromones used in the experiments was 5x10-10 (0.0000000005) grams/litre of water (or the equivalent of one teaspoon in 4,000 Olympic size swimming pools).

In October 2013 the researchers found the first lamprey spawning nests ever observed in New Zealand – or the southern hemisphere – in the Okuti River on Banks Peninsula. The researchers found the nest, laid on the underside of a large boulder, by following adults that had been marked with PIT tags the previous year. One nest was being guarded by an adult male, and Cindy suspects this is to do with protecting the developing eggs from eels. This is the first time this guarding behaviour by an adult lamprey has been observed anywhere in the world.

In late 2014 pheromone detectors placed in 12 Auckland streams returned positive results for lampreys in two of them, and a closer search found two juvenile lamprey in the Piha Stream and three in Glen Esk. “They’re not present in huge densities,” says Cindy “but they are definitely there.”

Maori know lampreys as piharau, korokoro or kanakana, and they are prized as a delicacy. There were special traps to catch lamprey in spring, when they are migrating for spawning, although declining numbers of lampreys mean it is not such a common sight on marae dining tables any more. Cindy relied on Maori with good local knowledge of lamprey migrating and breeding behaviour to source the animals used in the pheromone experiments.

The New Zealand Freshwater Fish database is a repository for information about all of New Zealand's freshwater fishes.

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