Often we hear about the number of fish species that eat algae growing on rocks. Most often we hear this discussion with Malawian and Tanganyikan fishes, though this feeding specialty is not restricted to them.
When we take a look at some of the cichlid books or other resources, we often see this food referred to as aufwuchs. In keeping our cichlids, it is important to understand, not only what aufwuchs really is, but how the individual species we are keeping, make use of this food source.
Aufwuchs is loosely defined as the biocover that grows on rocks. Its foundation is tough string strands of algae that are attached to the rocks. These strands form the building blocks of the biocover. Attached to the strands of algae are the items called "loose aufwuchs". The "loose aufwuchs" contains diatomous unicellular algae, but also microorganisms, insect nymphs and larvae, crustaceans, mites, snails and zooplankton.
Obviously this is quite the menu of food items, and many different fish specialize in certain portions only of this aufwuchs.
It is well worth noting that the fish are incapable of breaking down the outer walls of plant cells, without the help of microorganisms. In order to be digestible, the cell walls, must either be crushed, or broken down. The diatom algae have walls that are perforated, so they are broken down very easily. The fish, which do approximate to be herbivores, have numerous teeth that are used to crush the algae shells, to allow for their digestion. Despite this, quite a bit of the algae cells remain intact even after the food passes through the fish's body. Those fish that are the most dependant on the algal matter within the "Aufwuchs", have evolved to have much longer intestines. The longer intestines allow for more time to maximize the use of this slowly digestible food.
It must be noted, that even in
some of the most "herbivorous"
of fish, their growth is really
from the proteins found within the
aufwuchs, and not necessarily the
algae at all. The length of the
intestines in the individual species
though, does limit the amount of
proteins that can be broken down
safely, and care must be taken within
captivity with certain species.
There is a wide range of the use
of aufwuchs, though we can touch
on a couple of species, and how
they differ in feeding on what appear
superficially as the same diet.
Labeotropheus species have
a low underslung, well-developed
jaw that allows them more leverage
in grazing the aufwuchs. This jaw
allows the Labeotropheus
to completely pull off the strands
of algae from the rocks. The Labeotropheus
species are one of the closest to
being purely vegetarian in Lake
Malawi. At the other end of the
spectrum are Labidochromis
species, which feed off the same
aufwuchs. However, the Labidochromis
has developed their specialty into
picking out the items in the aufwuchs
which they have evolved to eat.
For the most part, that is the insect
nymphs and larvae. A sympatric fish
in Lake Tanganyika is the Neolamprologus
leleupi, who also grazes the
aufwuchs for the insect nymphs and
In between these spectrums are many fish that go from nearly completely herbivorous, to omnivorous, to nearly completely carnivorous, yet all use the same aufwuchs as their food source. While the algae "aufwuchs" is indeed the main food source for many fish, it is important to learn how this important food source is utilized for keeping your fish in the aquarium.