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Re: silversides

On Wed, 24 Jun 1998, Dwight Moody wrote:

Since I am on an anal surge today I figure I'll keep going.  :-)

> 1. These fish are physically set up for rapid bursts of speed, having an 
> extended torpedo shape.

Virtually all fish, irrespective of their overall morphology (shape) are
capable of rapid bursts of speed over short distances.
> 2. Being pelagic fish, they are very active, thus have a higher than 
> normal need for oxygen.

Pelagic is a term limited to ocean dwelling fish.  Pelagic is defined as the
open water area of the ocean.  By that definition freshwater critters are
excluded.  An equivelent term for freshwater doesn't really exist as far as I
am aware.

> 3. Early reports indicated that fish such as these are quite delicate 
> and the stress of capture causes significant mortality.

Nobody really knows why.  It seems to be mostly related to water temp in my
experience (or in other words I think that is the most important factor). 
Other suggestions made in the past include adding salt and not removing the
fish from the water, keep densities low, collect at night, keep densities low.  

> 4. Further investigation revealed that pelagic fish are VERY intolerant 
> of low oxygen levels and changes in temperature or water quality.  If 
> adequate O2 can be maintained, along with ensuring minimal temperature 
> and water quality changes, survivorship is greatly improved.

It varies.  One of the Australian species tolerates O2 as low as 0.5 mg O2 /
litre.  I don't think that generalization holds much water overall for
silversides (atherinids).  Anyway, if you avoid crowding and keep them cool O2
will not be an issue.

> 5. Stress seems to be a major factor in mortality. Water additives such 
> as Hypno and Ship Right, which contain mild sedatives, may be invaluable 
> in calming the fish and reducing stress and self-inflicted damage due to 
> impacting the walls of the container they are placed in. Both products 
> are available from Mail Order Pet Shop. Hypno is item #A2620, $4.99 for 
> 8 oz; Ship Right is item #A5708, $35.99 for 9 pounds.

This would certainly be an interesting thing to try.  Few folks seem to have
messed with sedatives.  One of the difficulties seems to be you need to bring
the fish back out slowly, if you do it rapid they apparently freak out a bit.
I've never done it, but that is what was said to me.

> 7. At some point in the near future, we should do a study analyzing 
> mortality and morbidity (i.e., death or disease/damage) using various 
> shipping systems and products to find out, scientifically, what works 
> the best.

But you can't control what the post office does with them inbetween.  Also,
it's near impossible to keep the shipping water conditions the same.  These
could be important details.  You would need to do it in such a way that they
weren't actually shipped but lived in a box for a few days and were driven
around in a car or something like.


Peter J Unmack 			peter.unmack at asu_edu
DESERT FISHES RULE: To boldly thrive where no other fish can make it!

Australian desert fishes pages at http://ozdesertfish.base.org (don't 
forget to visit the Desert Fishes Council pages too)
Native Fish Australia pages at http://www.nativefish.asn.au
North American Native Fishes Association at http://www.nanfa.org 
Aquatic Conservation Network at http://www.acn.ca

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