Zebra larva vision, brains and responses

Dallas E. Weaver, Ph.D. dweaver at crl.com
Mon Sep 30 18:20:12 EST 1996

We have observed that our zebra larva at high density (>100/l) in 1000 
liter tanks appear to try repelling each other and are attracted to 
the surface.  If they can't get away from their relatives they use up 
their energy reserves faster that they eat, hence they die.

In thinking about this observation, it appears that they are 
preprogramed to avoid other fish and that this program can interfer 
with the feeding response. We were also thinking about the vision 
system of these larva which should only have 2-D information.  Without 
knowledge of distance, there is no way that the larva can know whether 
what he sees is another small fish (no threat) or a larger fish futher 
away.  If it is a larger fish and he moves on a food animal, he would 
be eaten himself (creates an interesting choice).  When he is older 
with a more complicated brain, he could obtain information on size 
from fin and gill movement rates on a target that he sees.  

On some other larval fish, adding clay to the water improves survival. 
Could the same vision problem be solved by the clay with will allow a 
distance measurment, even with a simple brain. (water color doesn't 
improve survival).

Is anyone working on larval brains and vision.  This could be very 
relevant to larval aquaculture on many species.  Please contact if you 
are playing with this class of problems.

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