breeding the old fashion way

Christian Lawrence clawrence at rics.bwh.harvard.edu
Tue May 17 06:34:00 EST 2005


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Hi Leslie,

>From what I can gather, you are relying on an in-tank method to collect
embryos.   While this may seem to be the most straightforward approach, it
is actually more complex than other conventional spawning methods commonly
used in zebrafish husbandry due in large part to complex (and not
completely understood) chemical interactions that take place between 1)
males and females, 2) females and females, and 3) males and males.  There
are a number of things happening between individuals in your tanks that
can either enhance or suppress reproductive output, and if these things
are not actively managed, simple in-tank breeding strategies become
unreliable.

The first thing you can do to try and improve egg production is to use an
out-of-tank breeding method.  Try buying a few breeding traps - you can
get them from Aquatic Ecosystems or Aquaculture supply, among other places
- and setting up pairs or small groups of fish.  Whenever possible, mix
and match fish from different tanks.  Use fresh fish water when setting up
the crosses.  A 2:1 female to male ratio usually works well.  Set them up
together overnight, and they should spawn in the morning.  If they have
never been subjected to this before, expect that you might have to set
them up a few times before it works.

If you would rather stick with an in-tank strategy, you should 1)
continuously mix and match individuals (when possible) in tanks, 2)
decrease the number of males so that there a female bias in the breeding
tanks, and 3) do a 50% water change on the system the afternoon/evening
before the day you collect.

Your problems could certainly be due to water quality and/or diet, but if
your conditions are stable and within the generally accepted (and wide)
range for the species and your diet is reasonably balanced (has adequate
fatty acid and vitamin profile), it is likely the fish themselves that
need attention.

I've skimmed on this answer in the interest of brevity, so if you have
questions, let me know and I can respond off-list.

Good luck,
Chris

Christian Lawrence
Brigham and Women's Hospital
Karp Family Research Laboratories 06-004B
One Blackfan Circle
Boston, Massachusetts 02115

> --------------------------------------------------------------------------
>
> For the past couple of months our zebrafish have not been breeding very
well, if at all. Most of the fish are less than a year old. Our system
is a little archaic, 10 gallon tanks with whisper filters on the side.
We placed marbles at the bottom of the tanks and collect eggs by suction
in the morning 1-2 hours after lights come on. I am not really sure if
the breeding problem is the water conditions or the fish themselves.
>
>
>
> The water we use is instant ocean mixed with DI (2.4g/20L). We add in
some Kent pH stable (mostly bicarb) to maintain a pH of 6.5 - 7.0. Is
that too low?  The nitrate levels are very low. I am not sure what the
conductivity is supposed to be or how to adjust if it is not in a good
range.  Anything else I should be testing for?
>
>
>
> I must admit I am a bit of a novice and any help to decipher why the
fish are not breeding would be greatly appreciated.
>
>
>
> Much appreciated.
>
>
>
> Leslie Day
>
> Biology Dept.
>
> Northeastern University
>
> Boston, MA 02115
>
> l.day at neu.edu
>
> (617)373-3780
>
>
>
>
>
>
>
>

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