Well done! Killies, spawning viable eggs, are happy
killifish.
They are certainly still found in places like you
found them when the tide is in. They will thrive in
quite saline water. They also seem to do well in the
hard well water we have in Northern Illinois.
The issue may boil down to which kind of alkaline
water you can most effectively and frequently change
in their aquarium. If they thrive in your hard tap
water, just season it and change away. If the eggs
aren't viable or they begin flashing (scratching on
tank components), walk up the salt content.
Around here, we're increasingly using the feed salt
from agricultural supply stores. It is quite
reasonably priced, comes in sizable bags and is often
sun dried sea salt anyway.
Keep the collection location with them. Some people
feel that there are regional differences. There are
subspecific names given to them: F.h. macrolepidotus
(northern) and F.h. heteroclitus (southern). That is
paralleled by regional populations of Cyprinodon
variagatus and suggests a separation of those
populations for a time, perhaps during an ice age. Dr.
Stallsmith would know where the dividing line is and
the details of that.
If you Google Fundulus heteroclitus you will get lots
of hits. They have been used for all sorts of studies.
They even were on a 1985 Apollo flight to study the
effect of the absence of gravity on their swim
position and feeding. (Seem to remember that they
"solved" which way was "up" in zero gravity space by
orienting on their light source.)
By the way, in the salt marshes heteroclitus is a
spring and summer spawner. Wonder if the duration of
light in one's home and on the aquarium makes a
difference.
All the best!
Scott Davis
Park Forest, IL
Almost on the line between the Thorncreek and Kankakee drainages
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