[Zbrafish] Feeding and Breeding

christian lawrence clawrence at rics.bwh.harvard.edu
Mon Jul 24 13:04:56 EST 2006


Heather --

What you could describe in terms of suddenly reduced fecundity and fertility
could be one of any number of things:

1.  The fish are "aging".  If fish are bred intensively for extended periods
of time, they will hit a wall, usually somewhere between 8months and 1 yr
(or longer), depending on conditions and diet.   Zebrafish can live for a
long time in culture (up to 4-5 years according to some publications), but
in reality (i.e. the wild) this is essentially an annual fish, so
reproductive function is maximized early, as soon as they mature, peaks, and
then drops off. You can extend it in culture by maintaining favorable
conditions and feeding them a well-formulated diet, but the more stress you
put on them (handling them, collecting eggs, etc.) the quicker the drop-off
occurs.  

2.  The social situations in the tanks/breeding situations are stagnant.  If
you set the same groups of fish up repeatedly, particularly if they are held
together in the same tanks for long periods of time, social hierarchies that
can be counterproductive to production (all females breeding) will develop.
Mixing and matching breeding situations and holding situations will help
alleviate this, as will breeding them in "fresh" water (not from systems).
Doing the latter eliminates pheromones released by females that will inhibit
ovulation in competitors.


3.  Fish are cycling too rapidly.  If conditions are very favorable for
ovulation, and if you are not providing enough opportunities for efficient
oviposition in cycling females, they may start to become egg-bound, which is
when ripe eggs are not released, and are not completely resorbed.  What
isn't resorbed becomes necrotic, while at the same time the animal continues
to cycle new eggs and the problem gets compounded.  This is along the road
to the animal becoming terminally blocked.  The first sign of this, though
is reduced fecundity and greatly reduced fertility (if you measure what is
alive at time of spawning or day 1) because there may be partial blockages
of the oviduct to reduce egg number and ovveripe, partially necrotic eggs to
reduce "fertility".  This is especially likely if the females still look
ripe and you see the reduction in F&F.  One answer to this is to set them up
more frequently, with smaller breaks in between spawning events (females can
produce clutches of eggs every day in some situations).   You could also add
more males to holding tanks to increase efficiency of in-tank cycling
between out of tank events.

4. Diet.  This is actually the most important and most likely parameter to
be causing trouble in your and also in general situations.  To put it
simply, live diets are best.  People in aquaculture move to formulated feeds
to save money and time, but in typical zebrafish facility this ($ and labor)
is legible at the levels necessary for production - at least if you do it
right.   Formulated feeds are more likely to foul your water if overfed, and
at very least increase nutrient loading in your system (and feed your
cyanobacteria and/or algae).  This increased load can impact fish
performance.  Formulated feeds also have short shelf life, usually becoming
rancid or at minimum "nutritionally empty" (i.e. they are a nutrient source
for system and energy sink for fish b/c they expend more energy digesting
than they get out of it) after 1-3 months, if held at -20 or 4C.    Best and
easiest strategy for zebrafish, in my opinion, is to decapsulate brine
shrimp and feed out AS SOON as they have hatched (1st instar) 2-3x daily and
supplement 1x daily, with a nice formulated pellet, fed DRY, rich in vitamin
C, PUFA/HUFA, among other things.  By doing this, you will also drastically
reduce your organic load in the system.   If you are feeding 100% dry feed
to these fish, a switch to the above strategy will likely have immediate and
drastic results.

The above are just potential issues.  Could be combination of all 4, and
could be something else altogether.  But these are all likely and common
occurrences in zebrafish facilities.

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

-----Original Message-----
From: zbrafish-bounces at oat.bio.indiana.edu
[mailto:zbrafish-bounces at oat.bio.indiana.edu] On Behalf Of Heather S
McAllister
Sent: Monday, July 24, 2006 12:20 PM
To: zbrafish at magpie.bio.indiana.edu
Subject: [Zbrafish] Feeding and Breeding

We have been using a mix of Spirulina, Aquatox, Hikari micropellets,
cyclopeeze and golden pearl.  Our fish originally laid great with this
recipe, but lately we have been experiencing a problem with clutch size as
well as unfertilized eggs.  Some of our previously fertile fish have stopped
laying altogether.  We had received samples of both the Zeigler food from
AHAB as well as the danio mix from Aquadine.  I found the Aquadine settled
to the bottom and didn't filter out of the tank very well.  The Zeigler food
seemed to be a good alternative, but this morning I noticed a LOT of algae
build up in the tanks.  Within the last month we have basically cleaned
every tank, hose and gutter, to try and combat the algae problem we were
having and everything looked great for a while, but this weekend, the algae
just exploded.  
Does anyone have any ideas about food recipes, or do you find that you have
the same problem with Zeigler's?  I was thinking that maybe the fish have
grown too accustomed to the food we were feeding and switching to a new
formulation might increase the number fo fertilized eggs.  In the first few
days, they do seem to be getting better, but I think it is too early to
tell.  Thanks.
Heather McAllister
Laboratory Manager
Burdine Lab
Princeton University
Princeton, NJ

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