Pouched lamprey

The pouched lamprey, known scientifically as *Geotria australis*, is a fascinating organism belonging to the sole genus *Geotria* within the family Geotriidae. Indigenous to the Southern Hemisphere, this lamprey exhibits a unique life cycle: it begins life in freshwater, transitions to the sea as an adult, and returns to freshwater to spawn and subsequently die.

Physically, the pouched lamprey features a slender, eel-like body that can grow up to 60 cm in length. Unlike jawed fish, it possesses a sucker-like mouth. When freshly captured from the sea, adult pouched lampreys exhibit a shiny silver appearance, which turns brown in freshwater due to a pigment called biliverdin. A distinct characteristic of mature males is the development of a pouch under their eyes, which might be utilized during nest-building in the breeding season.

The life cycle commences with a larval stage known as ammocoetes, which reside in freshwater for approximately four years before transforming into silver-colored adults. During the macropthalmia stage, their brains undergo significant development, particularly in regions associated with vision. As adults, they inhabit the open sea, parasitizing other fish. Eventually, they return to freshwater to breed, demonstrating parental care for their eggs.

Pouched lampreys are found in various Southern Hemisphere locations, including New Zealand, Chile, Argentina, the Falkland Islands, South Georgia, and parts of Australia. Despite their broad distribution, they face threats from predators such as albatrosses, shags, large fish, and marine mammals. Additionally, there are concerns about declining populations, likely attributable to deteriorating water quality in their habitats.