Odd Mollies and Heater

[Charles]

I have a tank set up with a few mollies. I decided to plug in the
heater, and after an hour or so I noticed that the mollies had all
gathered around it and were nipping at it as if they were picking food
from it. A bit later I noticed that some of the mollies were lining
up vertically, with their bellies pressed against the heater, and
some in the near vicinity were going through the shimmying behaviour
I've read about. I wondered if it was an effect of the rising
temperature, so I unplugged the heater and plugged in a different one
at the other end of the tank. Molly behaviour returned to normal,
they established themselfes throughout the tank, not just around the
new heater.

Two days later I plugged in the first heater again, and within an hour
or so the mollies were again clustered around it, picking at it and
shimmying.

Unplugging it restored tank conditions to normal. Something about
that heater is strange, I wonder what it is.

In the same tank the bluefin killiefish showed no reaction, just the
mollies

[NetMax]

"Charles" > wrote in message
...
>I have a tank set up with a few mollies. I decided to plug in the
> heater, and after an hour or so I noticed that the mollies had all
> gathered around it and were nipping at it as if they were picking food
> from it. A bit later I noticed that some of the mollies were lining
> up vertically, with their bellies pressed against the heater, and
> some in the near vicinity were going through the shimmying behaviour
> I've read about. I wondered if it was an effect of the rising
> temperature, so I unplugged the heater and plugged in a different one
> at the other end of the tank. Molly behaviour returned to normal,
> they established themselfes throughout the tank, not just around the
> new heater.
>
> Two days later I plugged in the first heater again, and within an hour
> or so the mollies were again clustered around it, picking at it and
> shimmying.
>
> Unplugging it restored tank conditions to normal. Something about
> that heater is strange, I wonder what it is.
>
> In the same tank the bluefin killiefish showed no reaction, just the
> mollies

A few things come to mind. Was the opposite location different in terms
of currents, such that the heated water would be removed from the
vicinity of the heater faster or slower?

Heaters generate an electro-magnetic field. The electric field is not
very strong, being only 120Vac 60Hz but perhaps some fish can detect it.
I don't imagine the magnetic field is any stronger due to the spiral
shape to the wires, not entirely cancelling the fields but dampening
themselves a lot (if the wires were to cross each other, then the field
gets significantly dampened), but perhaps they are sensing it near their
threshold.

Last, least likely, some residual fungi, slime or other growths are along
this heater. Mollies are known to eat the protein layer at the surface
and munch algae, so we already know there is no accounting for their
tastes ;~).
--
www.NetMax.tk

[Charles]

On Sat, 3 Sep 2005 18:45:05 -0400, "NetMax"
> wrote:

(snip)
>
>A few things come to mind. Was the opposite location different in terms
>of currents, such that the heated water would be removed from the
>vicinity of the heater faster or slower?
>
>Heaters generate an electro-magnetic field. The electric field is not
>very strong, being only 120Vac 60Hz but perhaps some fish can detect it.
>I don't imagine the magnetic field is any stronger due to the spiral
>shape to the wires, not entirely cancelling the fields but dampening
>themselves a lot (if the wires were to cross each other, then the field
>gets significantly dampened), but perhaps they are sensing it near their
>threshold.
>
>Last, least likely, some residual fungi, slime or other growths are along
>this heater. Mollies are known to eat the protein layer at the surface
>and munch algae, so we already know there is no accounting for their
>tastes ;~).


The heater that affected the fish is located fairly near the sponge
filter, the one that didn't is at the other end of the tank (48
inches) The one that affected them is nearly vertical, the other one
is at quite an angle, so the first one could have set up a stronger,
less difuse, current.

I kind of suspect the electrical field, but I don't know how to test
for it, or what to do about it, other than not to use that filter. I
do have some test equipment, but making sure that I was not just
introducing more noise would be difficult.

It did look like they were eating growths from the heater, aufwufs, I
believe they are called, but they only did it when the heater was
powered.