embryo contamination

Monica Woo monicaw at exploratorium.edu
Tue Nov 19 19:21:59 EST 2002

Hello all.

I am having trouble with contaminated embryos and would 
appreciate any advice or information you might be able to provide.  

We breed two sets of fish every night.  The temp of the z-mod is 26 
C and the water bath for the breeding cages is 32 C.  We were 
having problems with the eggs becoming fuzzy and moldy after a 
few days. When we looked at them under a microscope, we could 
see small protozoan-like creatures swimming around the inside of 
the egg, presumably eating up the embryo.  This would happen 
anywhere from day 2 to day 4.  Initially, we thought there was 
some sort of contamination in the z-mod water we were using.  The 
hose that we use to get the water from hadn't been cleaned out and 
was full of all sorts of lovely creatures.  We stopped using the hose 
and started using water from the z-mod that had been sterilized 
from the UV filter already.  We would go a few days, but then the 
mold would return along with the small protozoans. Initially, we 
thought the small creatures were paramecium since we'd had 
paramecium contamination in a rotifer culture that we maintain.  

After still getting moldy, creature-filled embryos from the 
supposedly sterile z-mod water, we started using DI water treated 
with prime and baking soda to fill the mating cages to try to avoid 
whatever seemed to be in the z-mod.  This morning, the embryos 
from one mating cage were white and the embryos from the other 
other mating cage were healthy.  When I looked at the white eggs 
under a scope, they were full of the little creatures and already 
getting fuzzy.  The protozoan-like creatures are round, swim 
quickly w/ no obvious cilia and have a darker coloring.  They are 
small enough that probably about a hundred could fit in one 
embryo.  I may be able to take a photo of them if necessary.  

Is this some sort of parasite that some of the fish might be 
carrying? Whatever it is seems to be increasing as it usually took 
a day or two for the eggs to get white and/or fuzzy.  Today, the 
eggs in the breeding cage were only sitting in the water for a few 
hours and were very degraded by the time I looked at them this 
morning.  I also find it strange that one set of fish had healthy eggs 
and the other set had moldy/dead ones.  That tells me it isn't 
something in the water we're using, but something specific to 
certain groups of fish?  

Anyway, any help or advice you can provide regarding these issues 
would be great.  Thanks in advance!  


Life Sciences Lab Manager
phone: 415-353-0469
fax:  415-561-0370
email:  monicaw at exploratorium.edu


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