NANFA-- I. captive fish and breeding cycles II. migrations

Shireen Gonzaga (
Thu, 16 Dec 1999 17:13:12 -0500 (EST)

I. Captive fish and breeding cycles

In the wild, fish typically breed in the spring and
summer when food is plentiful. This is when males
usually take on their splendid colorations.

What triggers it? Is it something as simple as
daylight duration? Is it temperature induced?
Or are there other more complicating factors at
work? Has this ever been studied in a lab?

I'm asking because one of my mummichogs is starting
to get colorful. I've had him for almost 2 years.
My tank, heavily planted, gets 14 hours of light
and is kept at a constant 76F. It's fairly close to
a window so some indirect sunlight also filters
through. OK, so i've totally messed up his internal
clock with my artificial lighting and constant
temperature. But it's got me thinking about why
he's starting to color up in December.

II. Migrations

My second question is about basic fish migration.
Can anyone direct me to some references on how they
do it?

Speaking of migration... bird use many cues in
following their migratory routes. Before they start,
they display a behavior called migratory restlessness,
or "zugenruhe." In some species, this is manifested
as the bird facing a particular direction and flapping
its wings.

There are many factors that direct birds on their
journeys, such as the Earth's magnetic field, land
formations, daylight duration, the polarization of
sunlight, and even navigating by the stars!

As someone trained in astronomy, I find that last
factor especially appealing. In the 1960s, a student
at Cornell raised Indigo Buntings in a planetarium.
Instead of having the dome of stars rotate around
Polaris, the north star, he had them rotate around
Betelgeuse, a star in the constellation Orion. And
guess what... when the buntings matured and started
displaying migratory restlessness, their "north" was
in the direction of Betelgeuse!

This, of course, makes me wonder about the migratory
behavior of fish, and the factors that influence
their navigation. Comments and references would be
greatly appreciated.


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