Embryo quality

Dallas E. Weaver, Ph.D. deweaver at gte.net
Wed Feb 26 10:53:07 EST 2003

The most common cause of poor egg quality appears to be nutrition 
with the second most common being water quality issues.  

Keep in mind that any good quality dry feed with a good fatty acid 
profile has a short shelf life.  Old food will result in poor egg quality.  

Most of the aquarium diets that are used don't have a good fatty acid 
distribution (the manufactures get a good shelf life by not including 
omega-3 fatty acids).  If the fish are overfed with dry diets, all the water 
soluble vitamins will be leached from the diet in about 1 minute -- they 
have to eat it fast or it is no good.  

You really didn't say how crowded they were.  We have seen the 
fertility actually decrease when spawning fish at > 50/l (I think females 
start to knock eggs out of other females).  The water quality issue also 
relates to density in systems that have inadequate water treatment 
systems.  However, with properly designed water treatment systems 
you can grow out animals for brood stock at about 100 fish/liter without 
any problems.  

I do not consider 5 mo. old fish "young fish".  These fish can reproduce 
in < 50 days pf under optimal conditions.  


Sam England wrote:
> Dear All,
> I have several tanks of AB fish, aged 5 months, which I have
> recently begun to use for breeding, but I'm currently experiencing
> problems with embryo quality.  In my experience, I've often found
> that young fish produce low yields of poor quality eggs when first
> bred, but these fish have been set up about 4 times now, and still
> the quality is bad.  The embryos seem to be fertilised and begin to
> divide, however, the first cell is very small.  Subsequent cleavage
> events occur, but by the 4th- 5th cleavage events the cells have
> begun to bleb, and shortly after the embryos die.  Typically, these
> embryos are very dark compared to their normally dividing siblings. 
> The fish themselves are actually quite small, and I wonder if this
> is the problem.  We moved labs, but very little space was available
> for our young fish, such that they were grouped together in 1 tank
> from 2 months old.  I have only recently (within the last month)
> been able to divide them in to other tanks.  The fish are smaller
> than other breeds of the same age.  Our technician has increased the
> number of feeds the fish receive to try and improve their condition
> for breeding, but I would be interested to hear if other people have
> experienced similar problems with young fish, and whether they can
> offer any advice to remedy the situation.  I have only heard of
> copper toxicity affecting egg quality previously, but this doesn't
> seem to be a problem in our lab - other members have not reported
> poor egg quality.  
> Thanks for taking the time to read this message.  As I said, I would
> be grateful for any advice you can offer.  
> Yours in anticipation
> Samantha England
> PhD student - Developmental Biology Programme
> Department of Anatomy
> University of Cambridge
> Downing Site
> United Kingdom
> -
------- End of forwarded message -------

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