Pouched lamprey

The pouched lamprey, known scientifically as Geotria australis, is a unique fish from the Southern Hemisphere.

It is the only member of the genus Geotria in the family Geotriidae. In New Zealand, this fish has several local names. People in the North Island call it piharau. In the South Island, it is known as kanakana or korokoro. It is also sometimes called the wide-mouthed lamprey. This species is quite different from most fish because it lacks jaws. Instead, it uses a sucker-like mouth to attach to other things.

The life cycle of the pouched lamprey involves several distinct stages. It begins as a larva called an ammocoete. These larvae are a dull brown color and live in fresh water. They remain in this stage for approximately four years. After this time, they undergo metamorphosis, which is a major physical change. During this six-month process, they develop silver skin with blue-green stripes. Their central nervous system also changes significantly during metamorphosis. They enter the macropthalmia stage, which is characterized by much larger eyes. This stage also involves a large increase in the volume of the brain's visual areas.

Once they reach the macropthalmia stage, the lampreys migrate downstream to the sea. As adults, they live in the open ocean for a period of time. During this phase, they act as parasites on other fish. They attach themselves to the gills or the sides of a host fish. Once attached, they use their mouths to rasp at the tissues of the host. This allows them to feed. The adult's skin color depends on its environment. When caught fresh from the sea, the skin appears a striking silver. However, the skin soon turns brown after the fish enters fresh water. This color change is caused by the deposition of a substance called biliverdin.

After living in the sea, the adults return to fresh water to spawn. They may spend up to eighteen months sexually maturing before they are ready to breed. The males have a unique physical feature used during this time. They develop a baggy pouch located under their eyes. Scientists believe this pouch may be used to massage and oxygenate the eggs. In some northern hemisphere species, the pouch might even help gather stones for nests. After spawning, some adults provide parental care. They have been recorded wrapping their bodies around egg masses. Some adults live for up to 105 days after they have spawned.

The pouched lamprey has a very wide distribution across the Southern Hemisphere. You can find them in New Zealand and Australia. They are also located in Chile and Argentina. Other populations exist in the Falkland Islands and South Georgia. In New Zealand, the pouched lamprey is the only lamprey species present. However, there is another species in the genus Geotria called the Argentinian lamprey. This second species, Geotria macrostoma, was revalidated as a separate species in 2020.

Humans have interacted with these fish for a very long time. In New Zealand, the pouched lamprey is a traditional Māori delicacy. Māori people developed specific methods to catch them. One method involved disturbing the lampreys as they climbed up waterfalls. Another method used a weir, which is a structure placed across large rivers. This weir would lead the fish into a hīnaki, which is a woven trap. By the mid-19th century, European settlers in New Zealand also began eating them. They adopted the lamprey as a food because it was already a popular delicacy in Europe.

Today, the pouched lamprey faces certain environmental challenges. They are part of a food web where they are preyed upon by many animals. Albatrosses, shags, large fish, and marine mammals all eat lampreys. There is also a concern regarding their population numbers. Scientists have hypothesized that a decline in lamprey numbers might be linked to the environment. Specifically, the degradation of water quality in lowland waterways may be a cause. Protecting the quality of these fresh water habitats is important for the survival of the species.