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a comparison of two algae-eating fish


Traffic on the list has been real light lately, so I guess I'll wade in
with an unsolicited post.

A few months ago I rebuilt two 10-gallon tanks that I previously used
partly for comparitive experiments.  I posted a letter at that time
describing some of my experiences with the two tanks.

When I rebuilt the tanks I gave them identical equipment and substrates,
similar plant densities (but not identical plant species) and similar
maintenance. I populated one tank with four American Flag fish (Jordanella
Floridae) ranging in maturity from small juvenile to full adult and one
with three female adult swordtails (the venerable Xiphophorus helleri).
Both fish eat some types of algae.  The plants used in both tanks carried
some algae from the previous setups and it was soon evident that there
were considerable differences between the ability (or will) of the fish to
remove the algae.

Diatoms grew in both tanks and none of the fish showed an interest in
picking at the brown film.  Plants in both tanks carried small but
noticable infestations of green hair algae, black brush algae and beard
algae.  A coarse dark algae I would call staghorn algae and a fine, short
filamentous black algae appeared later in in both tanks.

The Flag fish quickly removed all signs of the green hair algae from their
tank.  The staghorn algae made a brief appearance in the Flag Fish's tank
then disappeared.  I never saw them eating it, but who can say what they
might do when my back is turned?  The beard algae also made a brief
appearance and then disappeared.  I think I've seen Flag fish eating beard
algae before, but I don't know in this case if the fish removed it or if
the algae simply failed to thrive in the new setup. The Flag fish showed
no interest in the black brush algae and it grew on older leaves from a
small presence to very noticable bushy clumps.  The black brush algae
didn't appear on new leaves and I eventually removed the older leaves, so
now it's gone.  The Flag fish also show no interest in the fine, dark
filamentous algae and that is starting to become a nuisance on some older

The swordtails removed every sign of black brush algae from the older
leaves in their tank.  They also grazed on the green filamentous algae --
enough to keep it in check, but not enough to eradicate it.  I removed the
little bit they left.  Beard algae and the short, black filamentous algae
both made brief appearances in the tank and then disappeared.  I think
that swordtails grazed both types of algae, but I can't say how much of
the algae's disappearance was caused by grazing and how much might have
been due to the algae's failure to thrive in the tank.  The swordtails may
have nipped at the staghorn algae a little but otherwise they showed very
little interest in it.  The staghorn algae is now gone; I think that once
the tank got established that the staghorn algae simply failed to thrive.
The swordtails' tank is now pretty-much algae-free.

Both types of fish will eat plants.  The swordtails nipped the ends off
the fine leaves of R. wallichii; their constant nipping and cleaning also
uprooted some pearl grass (graciously given to my by Tom Barr) and made it
a little difficult to get the pearl grass started, though that problem
seems to be over now.  The Flag fish turned out to be real fans of dwarf
hair grass (also donated by Tom Barr) and I suspect they would have gone
for the R.  wallichii with at least as much gusto as did the swordtails.
The Flag fish also tattered the edges of C. wendtii leaves and I've seen
Flag fish in other tanks do the same thing to Val. americana leaves.

In my tanks the female swordtails did a better algae-eating job than the
American Flag fish - even cleaning up the dreaded BBA.  At this point the
swordtail tank is pretty much clean but I still have a little problem with
a short dark filamentaous algae in the Flag fish tank.

Roger Miller