And more, right? Water chemistry. Spring rains, or freshets (a surge of
mountain runoff or upper watershed rainfall) can stimulate activity. Also,
remember when Jan was talking about how his flagfish get all frisky when he
does a water change?
Then there's the presence of other spawning fishes in the case of some
minnows (presumably milt released into the stream is the cue). Some
Notropis (and Phoxinus?) species don't become sexually active until
nest-building minnows like Nocomis and Semotilus commence their own
> >My second question is about basic fish migration.
> >Can anyone direct me to some references on how they
> >do it?
> This sort of depends on the scale you are interested in, and
> varies from the
> incredible ability of Anguilla to navigate through open ocean to
> the ability
> of tidepool fishes to home back to their tidepool after
> displacement. They
> can use cues like smell, water currents, temperature and salinity
> celestial cues, plane-polarized light, and magnetic field
Here are some notes on celestial and magnetic field cues:
1) From "Evidence for celestial and magnetic compass orientation in lake
migrating sockeye salmon fry", by Thomas P. Quinn. 1980. Journal of
Comparative Physiology 137: 243-248.
Sockeye salmon either spawn on lake gravel reefs or in streams upstream or
downstream from a lake. When the eggs in streams hatch, the fry swim to the
lake. Whether it's upstream or downstream, they know which way to swim.
They then spend a year in the lake before swimming to the ocean. Quinn
tested the celestial and magnetic components of freshwater migration. He
found that the sockeye fry in his experimental setup swam in a direction
that would have corresponded to the direction they needed to find their
lake. They swam the same way whether at day or at night, and in containers
open to the sky or ones with plastic covers.
Then he experimentally changed the tanks' magnetic field 90 degrees, and
found that at night the fish movements changed with the new magnetic field.
But during the day only the ones in covered tanks (no view of the sky)
behaved as the ones did at night. The ones in uncovered tanks (a view of
the sky) adjusted and swam in the proper geographic direction in spite of
the altered magnetic field.
2) From "Experimental evidence for juvenile chinook salmon, Oncorhynchus
tschasytscha Walbaum, orientation at night and in sunlight after a 7 degree
change in latitude", by P.B. Taylor. 1980. Journal of Fish Biology
Taylor basically found the same thing with chinook salmon. He concluded
that directional information from the earth's magnetic field and sunlight
provides a complimentary cross-reference.
If anyone wants these papers ask me off list and I can scan or photocopy
-- Jay DeLong Olympia, WA
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