question about zebrafish breeding

[Dallas Weaver, Ph.D.]

in article 9qfign$alm$1 at mercury.hgmp.mrc.ac.uk, Dr Peter Cattin 
at p.cattin at auckland.ac.nz wrote on 10/15/01 1:55 PM:

Peter,

The goldfish pheromone work was done  at Oak Ridge National Lab 
in the 70's and I can't find my copy of the report.  I seem to 
remember that it was part of a MS Thesis.  He used a crude 
extract (eliminating ammonia and the other common waste 
products) from high density fish water and showed impact on 
respiration, heart rate, metabolisms rate, etc.  

The point about the bacterial habitat specifications(ie filter surface 
area and mass transfer requirements) becomes very complex when 
you start trying to understand what is happening to the waste 
components other than the ones that you can easily measure (ie. 
ammonia, nitrite).  With pure ammonia feed and only enough P, K, 
and Fe for the bacteria, you can get ammonia oxidation rates in the 
1 to 2 gm/m2 day range, on most thick film media.  However, with 
real fish waste (that contains a lot more that just ammonia) the 
rates are down by a factor of 5 to 10 on the same media at the 
same substrate concentrations. This is related to competitive 
exclusion and related problems where the faster growing bacterial 
species (using either more degradable substrates and/or higher 
concentration substrates) out compete the slower growing bacterial 
species for habitat in the biofilms.  This same phenomenon occurs 
in industrial waste treatment where you have something easy like 
benzene mixed with water with something that is more refractory 
like MTBE (methyl tert butyl ether -- a gasoline additive that 
contaminates groundwater).  

This subject get into the details of the system design and whether 
the biomass and/or the water are operating plug flow or a mixed 
reactor. We have a indication from some species of animals that 
reproduction is better when we have enough internal surface area to 
eliminate competitive exclusion problems.  We also have some 
indications that some either very low concentration or refractory 
components with bacterial kinetics slower than ammonia/nitrite 
may be relevant the the animals performance in tightly closed 
systems.  

Pheromone and other trace waste products are a relevant 
questions after ammonia is not an issue.  I assume that any well 
designed research system will not have any ammonia problems.  
Even in commercial systems, ammonia should not be a problem.  
Our recycled water is normally < 0.1 ppm ammonia (N) (ie ND on 
our equipment) at all times.  We also expect nitrite to be < 0.02 
and if it isn't it is time to check out the system (a management 
action set point).   

I did the growth experiment at 28 C only because one of my 
customers was using 28 C.  I also did an experiment at 22 to 24 C 
(variable ambient) with an egg to egg time of 65 days.  I know 22 C 
is a bit on the low end of the growth curve.  You only get the 
advantage of 28 C growth rate if you have the food (bioenergetic 
aquaculture models provide some useful concepts relative to this 
problem -- at high enough temperature the animal can have 
maximum feed rate with no growth).  With the less than ideal 
feeds, lower temperature in the 25 C range with give adequate 
growth rates with fewer problems and it will be more comfortable for 
the staff.  My commercial zebra production runs an egg to egg time 
of about 90 to 100 days at 22 to 24 C with most of the growth being 
on dry feed at densities > 75/liter.  

Dallas

Dallas E. Weaver, Ph.D.  <deweaver at get.net>
Scientific Hatcheries
5542 Engineer Dr.
Huntington Beach, Ca 92649 USA
714-890-0138
Fax 714-890-2778

> A point in your comment, Dallas, that I think is non-sequitur. 
> There is no doubt that maximum growth requires optimal water
> quality, and that an important part of this process is the provision
> of an adequate substrate (space) for the bacteria  required to
> remove metabolic wastes etc.  It would be reasonable to assume that
> an inadequate supply of these bacteria will negatively impact on the
> growth rate and general health of the fish.   I would suggest
> though, that the relationship between an inadequate supply of
> denitrifying bacteria and goldfish producing growth inhibiting
> pheromones is pretty tenuous.  A single fish in a large volume of
> poor quality water will not grow well without pheromones.
> 
> Do you have references on the goldfish pheromone phenomena as I
> would like to read about it?
> 
> Finally, you have remarked on the "why 28oC temperature" for
> growing zebra fish - which is a point that was puzzling me, yet
> there does seem to be some truth in the excellent growth rate of
> zebra fish at this temperature.  Any ideas as to why?
> 
> Thanks and regards,
> 
> Peter Cattin
> --
> Peter Cattin PhD
> Division of Molecular Medicine
> Faculty of Medical and Health Sciences
> University of Auckland
> Park Road, Grafton, Auckland.
> Private bag 92019, Auckland,
> New Zealand.
> 
> Tel: +64-9-373-7599 xtn. 6373
> Fax: +64-9-373-7492
> 
> "Dallas Weaver, Ph.D." wrote:
> 

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