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SAEs

>I'm wondering, why do the SAE, flying fox, otocinclus
>etc have such similar markings, yet are from a variety
>of families? What is it about the algae-eating niche that
>brings about this evolutionary convergence?

>(I don't expect a totally definitive answer.)This pattern is not at all
limited to algae eating fish.  It is extremely common in   fish from a
diverse number of ecological niches.  I can tell you pretty certainly about
the light under body and dark upper body.  It's a pretty standard trick
among fish.  Lokking down though the water, it's hard for a predator to see
a dark fish against the dark substrate.  Looking up from the bottom, it's
harder for a predator to see a light body against the back lit surface.
One noted exception to this pattern in Synodontis nigriventris, which, as
it's name implies, is dark on the ventral surface, (or belly) and light on
the dorsal surface.  In this fish, the reverse coloration makes perfect
sense when you put it together with the fact that these fish swim
upside-down most of the time.

Observation of many species leads me to be that horizontal striping is a
schooling cue.  It is seen in many, many schooling fish, and much less
often in non-schooling species.  Interestingly, I kept a group of Corydoras
robinae and a school of Petitella georgiae (rummy nose tetras) together for
a while, and they all schooled together.  My only guess is that they were
cueing off the horizontally striped tails, even though they are _totally_
unrelated fish.

Look at how many small native schooling fish display this same color
pattern.  You can find a minnow or shiner in almost every stream and lake
that fits this basic description.

Karen Randall
Aquatic Gardeners Association