 |
Bits & Pieces
 |
|
 MAGNETIC SENSING
IN FISH
Biology & Beyond -- A study by biologists from New Zealand* indicates how the magnetic sense in fish, which is used for homing and long-distance migrations, is organized. Particles of magnetite, an iron-containing substance, are arranged in tiny rods embedded in four cells, located just beneath the cells lining the flaps within the nose. These rods orient to the earth's magnetic field. We don't know how signals from the magnetic detector are processed in the brain.
Although the existence of a magnetite-based magnetic receptor system has for decades been recognized in birds, some scientists doubted its function because birds are known to use a sun compass for orientation during migration. It's now recognized, however, that the magnetic sense in birds is a standby navigational system that goes into action if the sun compass isn't operational.
Trout, salmon and other fish use olfactory cues (acute sense of smell) to return to the streams in which they were born. The magnetic receptors and olfactory receptors are located almost on top of each other in the nose. Perhaps these systems work together, or perhaps fish have a navigational standby system similar to the system in birds.
*Walker, M. M., et. al. 1997 Structure and function of the vertebrate magnetic sense. Nature 390:371-376.
Bruce Carlson
Illustration by Ron Finger
 WORLDS' LARGEST SALMONID IN DANGER
International Science -- An international research team of ecologists is spending the next five years studying the world's largest freshwater salmonid, Hucho taimen, in Mongolia. Taimen, which may reach six feet long and weigh over 200 pounds, are known for their tremendous aerial displays when hooked.
Taimen numbers have declined as a result of habitat destruction and overharvest. On a recent expedition to the country, however, the research team discovered 15 adult taimen in a stretch of the Tuul River the size of a football field, a surprising discovery, since large taimen have been thought to be territorial. Normally, only one large taimen occupies a stretch of any river.
This find would be welcome news, as it could mean population size is healthier than thought. On the other hand, such a concentration of large fish leaves this species vulnerable to poaching.
Using radio tags, underwater observation, and local knowledge, the research team hopes to learn more about taimen. Hopefully, the results of this study can be used to promote catch-and-release fishing and ecotourism in this new democracy, meanwhile helping to conserve this threatened species.
|
|
|
|
|
| |
