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Re: Prematurely Hatched Australe Frys
I have a guess or two about this subject. [When don't I?]
Premature hatch must be due to a breakdown in the shell (chorion) before it
should happen. I suspect the normal hatch involves digestive enzymes of some
kind weakening the chorion so the larva can kick free at the proper time and
If external conditions cause that weakening, prematurely, then the baby
becomes unprotected and has to finish absorbing the yolk outside the egg.
[That, BTW, is quite common in eggs that are parentally protected, like most
My favorite candidate for the culprit is bacterial action on the egg. Warmer
conditions often speed up the process.
I never seem to see it happen, if I have kept the environment moderately clean
and bacteria free. That can be via dyes (acriflavin/methylene blue 50:50 is my
favorite) or by a sprig of Java moss and infusuria (filter feeders) that eat
up all the free-swimming bacteria in the hatching tray.
Fungus quickly envelopes early-death eggs, but later on the baby may have
enough immunity to keep it away. IDK. Fungus, itself, never kills eggs, AFAIK.
It is a result of bacterial death (or infertility and bacteria) and *then* it
appears. Most of the true fungus we see on fish or eggs does not grow well on
living tissue. It thrives on dead cells, tho.
One other external factor that I think might cause premature hatch is total
dissolved solids (tds) change. The same problem fish have if you suddenly dunk
them in "softer" (i.e., lower tds) water could put internal osmotic pressure
on the egg as that low tds water tries to dilute the saltier liquids inside
the egg. The excess pressure could burst or weaken the chorion. I'm usually
careful not to shock eggs with big, sudden tds change, any more that I would
If I want to hatch in mostly RO water, I'll do two or three 50% dilutions from
the original tank water, at half-hour or more intervals, to make it easier on
the eggs. [I never deliberately use pure RO water in the fishroom, BTW. It is
way too reactive and needs a trace of tap water to keep the tds from being too
low for safety.]
The dyes are deceptive, as they tend to cross-link chorion molecules and
toughen the egg. It's hard to tell if that or bactericidal action causes the
effect. Overdo the dyes just a little bit, and many killies never kick free
and hatch. It is much like the hardening presumably cause by Ca or Mg in hard
water. The shell gets too tough. I dilute it out quickly, if I use it at all.
Seriously stained eggs are a warning.
That's my US$0.02,
LadysSolo at aol_com wrote:
> I have occasiionally had fry hatch prematurely. If the yolk sack is small
> they sometimes survive and grow normally. I found it to be at least somewhat
> temperature-related in that it occurred more often in hatching containers in
> warmer locations (but not always.) And it does occur in other species. I had
> it occasionally in Rivulus and South American annuals. Can't help other than
> that. Carolyn
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