Re: Great in the air, not so good underwater

[evelyn sobielski <koreke77@yahoo.de>]

> Oh, I agree that it is compatible with an
> evolutionary path towards 
> improved flight; I'm merely saying that they
> probably aren't actually 
> powered flyers, and hatchetfish might not even be
> gliders.  The 
> enlarged pectoral fins might be utilized for some
> other function.

Having kept some years ago, they do certainly not need
them for swimming, underwater navigation etc much; the
pectorals are a bit of an over-adaptation for
swimming; a lot of fish have these but fairly
randomly; it seems an overall OK feature but nothing
dramatic. The body shape on the other hand might have
other uses, like camouflage (they heve a fairly
un-prey-like shape if seen from forwards). They have a
capability to utilize the water-air-boundary in a
peculiar way though, apparently from the combination
of these 2 major features (and some others, like head
shape etc); they do not leave the water any more than
other fish do (i.e., they jump), but they *might* be
able to feast on swarming insects better than any
other fish in Amazonia. They apparently find it easy
to rise out of the water with the top 30-50% of their
body, obliquely (tail down) and routinely pop out
their heads a bit if there's something going on above.
They can jump well, but they are also able to cruise
around semi-emerged like little speedboats. They don't
breed easily in captivity; feeding them copious
amounts of dipteran larvae helps a lot (I didnt breed
them, we had a crude mix tank :( ) which is
interesting to note (IONO if detailed data on food in
the wild exists); they do not eat large amounts of
fruit AFAIK and they are not bottom feeders. They do
not descend deeper  from the surface than maybe 4, 5
times their body height usually.

Regards,

Eike




        
                
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