Problems with zebrafish spawning

PZ Myers myers at
Wed May 27 19:07:17 EST 1998

In article <6kel1c$eaf at>, Steve Baker <sbaker at> wrote:

> We are trying to successfully spawn zebrafish and to date have been
> quite frustrated.  Our fish have been on the light cycle for almost two
> weeks, fed 3x daily (twice on flake food, once on frozen brine shrimp),
> held at 26-28 degrees C. They are very plump and seem to be
> healthy. Males are nice and yellow.  A net has been placed in the tank
> to allow the eggs to fall through to the bottom (the protocol we were
> given discourages the use of marbles). Tanks are siphoned daily to
> keep clean.
> To date have not found any eggs (except brown brine shrimp eggs :)  ).
> Some questions:
> 1.      Are the eggs large enough to see easily with the naked eye?  
>     Can you give us a general idea of their size? We have been siphoning
> up bottom debris but have not seen
>         any yet.

They are visible to the naked eye, but you have to know what to look for--
they are small and transparent, so you are trying to see little pearly
dots. The best thing to do is to throw some of the debris you've siphoned
up onto a dissecting scope, where they are unmistakeable, until you get
familiar with their appearance.

> 2.      Is there any noticeable spawning behaviour to watch for?  
>         We have been checking from "dawn" until about 2 hours later, 
>         have seen some "chasing" behaviour, but that's about it.

Yes, there is a kind of frantic chasing going on, with the males 
hugging the flanks of the females very closely. At fertilization,
you can often see a little explosion of milky, filmy material which,
if you are having trouble seeing the eggs, might not be too noticeable
to the inexperienced eye. What you will easily see, though, is all the
other fish darting in to the site to get a caviar snack.

We've been having regular shows at my lab. The lights come on at 2:00
for one set of tanks, and we go in to watch the orgy. They typically
perk up *very* quickly when the lights come on, and mating occurs within
5-15 minutes.

> 3.      Any ideas concerning what we may be doing wrong?  So many
>         of the internet "how-to" guides make this seem so easy,
>         we fear we must be overlooking something important!
> We would really appreciate any ideas.  We are eager to incorporate
> zebrafish embryology into some zoology labs this fall.

I wish I could tell you what is going on...our fish go into funks
every once in a while (well, way too often, anyway!) where they are
just plain unresponsive. The only way we've gotten around it is to 
have enough fish available that if one set are getting cranky we can
move on to another bunch.

PZ Myers

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