[Zbrafish] Chordal structure Malformation

Christian Lawrence via zbrafish%40net.bio.net (by clawrence At rics.bwh.harvard.edu)
Wed Nov 22 08:15:51 EST 2006

While the phenotype that you report certainly could be the result of
exposure to some toxin, I would recommend ensuring that your baseline
parameters  -  water quality and diet - are in order before proceeding any
further.  I am always a bit skeptical of the generic toxin explanation
routinely offered up by folks when they start to see sudden, across the
board problems in their fish populations.   In so many instances (both
mysterious developmental abnormalities of the embryos/fry and acute disease
outbreaks), there is some simple problem with water chemistry and or diet
that is at the root of the problem.  Also, toxins are unlikely to be the
culprit in instances where the effect crops up in the absence of any notable
change in husbandry (where would the toxin be coming from?).    The main
point that I am trying to get across here is that when trying to unravel
this problem, start with the simplest, most basic issues and go from there.
It may very well end up being some heavy metal, but you don't want to waste
time exploring this if the problem is that you've been unwittingly feeding
your fish rancid flake food, or if your nitrites are sky high, for example.

With this sentiment in mind, you should go through your water quality data
and look for potential problems there.  Are your ammonia and nitrites zero?
Is the pH stable?  What are the parameters of your source water?  Has there
been a change with this, or has it been stable?  And so on..

As for your diet, what are you feeding?  Have you changed anything?  How do
you store your food?  How do you feed it?  In general, feeding zebrafish a
combination of live zooplankters (like Artemia) and a decently formulated,
fresh, and properly administered artificial feed is usually enough to
support steady production.  So many people working with zebrafish don't
fully appreciate how important it is to handle artificial feeds properly.
These diets are perishable, and must be kept at 4 C to maintain the typical
maximal shelf life of 3 MONTHS.  And because certain nutrients (i.e. vitamin
C)in feeds are susceptible to rapid leaching upon hydration, they also must
be administered properly.  This means feeding them dry, unless they are
encapsulated (typically only very small particles), in which case they can
be hydrated and fed in a slurry with a squirt bottle or dropper.    These
things become even more crucial if the artificial feed is the sole dietary
item for your fish, because if you're not doing it right, the diet that you
think is "balanced" isn't really so balanced because you're not getting some
fraction of the nutrients in the feed to the fish as a result of spoilage
and or leaching.  The kicker here is that the obvious effects of such
nutrient deficiencies may not be gradual...

At any rate, in my opinion, the best way forward is make sure that these
parameters are satisfactory, and then go from there.

I'm glad to answer any further questions on this off-list if you wish.

Good luck,

Christian Lawrence
Brigham and Women's Hospital
Karp Family Research Laboratories 06-004B One Blackfan Circle Boston,
Massachusetts 02115
Tel: 617.355.9041
Fax: 617.355.9064

On 21 Nov 2006 04:51:51 -0800, françois <busquet.francois At gmail.com> wrote:
> Dear all,
> since one week, a third of my fish embryos incubated in fish medium at
> 26°C,  developed chordal structure malformation like a ,,zigzag"
> after 24hpf. I didn't know from which aquarium it comes from because
> I collected all the eggs from the boxes in one big petri dishe.
> Therefore, I first checked in which aquarium this could come from. I
> collected once again fish eggs depending on the aquarium origin and I
> incubated the fish eggs in fish medium at 26°C.
> Today, I figured out that more than 80% fish embryos displayed again
> chordal structure malformation for every aquarium. Moreover, I changed
> all the population for one aquarium last weekend and replaced by
> younger ones (around 8 months) but in the same water. It didn't make
> any differences, the chordal malformation was also for 80% of fish eggs
> for this aquarium.
> We use a static system where fish medium is totally replaced every 15
> days. The fish medium is based on deionized water + CaCl2 + MgSO4
> (with Ca:Mg ions is 4:1) + NaHCO3 + KCl (with Na:K ions is 10:1). I
> heard that chordal structure malformations could be linked to heavy
> metals presence or from some infectious diseases or even vitamin
> deficensies.
> Any comment are very welcome!
> regards
> françois busquet
> PhD student/ Ecotoxicological Institute/ Merck KgaA/ Germany.
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Christian Lawrence
Brigham and Women's Hospital
Karp Family Research Laboratories, 06-004B
One Blackfan Circle
Boston, MA 02115
Tel: 617.355.9041
Fax: 617.355.9064
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