Sea lampreys unable to find their way home

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Sea lampreys lack the homing abilities seen in other anadromous fishes, according to the results of a new study.

Anadromous fishes, such as Atlantic salmon, Striped bass and White sturgeon, are born in freshwater, but spend varying lengths of time there before migrating to the sea to mature into adults. They finally return to their native freshwater homes to breed and die.

However, scientists in New York have discovered that the Sea lamprey, Petromyzon marinus, is an exception to the anadromous lifestyle in that it appears to lack this homing ability.

John Waldman, Cheryl Grunwald and Isaac Wirgin analysed DNA portions from over 300 lampreys in 11 different North American rivers. If lampreys did home into their native rivers, the results should have shown a significant difference in DNA between the different rivers. However, Professor Waldman s study found no significant difference between populations.

Benefits of migrationAlthough there are many risks associated with migrating between the two environments, there are also great benefits in terms of avoiding predation in early life stages, as migration is often coordinated, and increased access to food and energy sources as they move to the marine environment to mature.

There haven t been a great deal of studies done on the homing mechanism in a great number of anadromous fish but research on salmon and sturgeon have shown that they use smell to draw them back to their birth river when they are returning for spawning.

Sea lampreys are different to most of these fish, in that they bury themselves for up to eight years in the mud of the freshwater rivers before they transform into a parasitic form which feeds on the blood of other fish.

The variety of hosts for this species is massive but includes, Atlantic salmon, Bluefin tuna, Basking sharks, Mackerel and whales. As few of these fish share seasonal migration patterns, this gives the lamprey the potential to travel huge distances on the bodies of their prey. As a consequence of this, lampreys have been found from the surface of the ocean right through to depths of 4000 metres.

Bile acidIn a survey of the Great Lakes only 8% of the tributaries were found to be suitable to sustain a population of Sea lamprey larvae. So how do lamprey s find their way to a suitable spawning site bearing in mind they migrate far and wide?

Strong evidence suggests that the adult lamprey ~home in on bile acid released by already hatched larvae in rivers, with individual larvae ~activating up to 400 litres of water per hour. Adult males then swim to the spawning sites and release powerful pheromones to attract the females.

This study may have significant implications for areas where parasitism by the non-native lampreys has caused significant economic damage such as the fisheries of the Great Lakes. In this situation, the release of lamprey pheromones in unsuitable spawning rivers may result in highly unsuccessful breeding efforts and a subsequent decrease in lamprey populations.