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An
Article by George J. Reclos, Andreas Iliopoulos & Michael K. Oliver
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Feeding
your fish is not as easy as it sounds. It is a complicated
issue that requires you to know which is the best food for
each fish, what its system will metabolize most efficiently,
and which food will give the fish the essential and
nonessential elements that are all vital for its well being.
To get the best results there are two things you should know:
What your fish eats in the wild, and why it is important to
follow specific feeding procedures, as well as using specific
foods.
There
are two main groups of fishes according to feeding
requirements: the Carnivores
(flesh eaters, predators)
and the Herbivores (plant
eaters). We may also form a third group, the Omnivorous
species that use a broad spectrum of food resources. Even so,
there is a vast diversity among the biotopes that constitute
natural ecosystems, the species that inhabit them and how they
eat and are eaten. This
classifies some species as specialized
feeders due to their particular sources of food and the
methods they use to obtain it.
Predators
may feed on invertebrates, mollusks, insects, plankton, and
finally, other fishes. These we can define as general invertebrate feeders, molluscivores (snail feeders), insectivores
(insect eaters), zooplanktivores
(zooplankton eaters), and piscivores
(fish eaters).
Some
species sift for
invertebrates (Geophaginae);
others hunt them (Pagellus
bellotii), or pick
them with their sensitive vibration detecting organs (Aulonocara
spp.the African peacocks), while some just browse
upon them (Neolamprologus cylindricus).
Some
of the molluscivores have strong jaws and teeth so that they
can crush snails (Neolamprologus tretocephalus), while others
have mouths that are constructed in such a way that they are
able to suck
mollusks out of their shells (Botia macracantha; the
clown loach).
Insectivores’
tastes differ a lot from species to species. Some consume
insects when they are either eggs or larval stages, while
others eat the adult insects. Many of them consume insects in
all the forms of their life cycle. The mouth of such species
is directed upwards so that they can easily prey on insects on
the water surface (Gambusia spp). Usually fishes, as
fry, are fed on insects while they are in egg and larval
forms.
Some
of the more specialized feeders are fed on adult insects
located over the water level. They capture them either by
jumping (Osteoglossum bicirrhosum; the Silver
Arowana) or by spitting water on them (Toxotes jaculator).
Adult O. bicirrhosum jump out to catch birds and
arboreal mammals as well.
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Plankton
is found in either free-swimming form or on different
substrates, so planktivores have either to pick at
it (Cyprichromis spp.), suck
it from the substratum (Gnathochromis permaxillaris),
or filter it
through their suitable pharyngeal teeth (Cyprinodontidae) or
their filamentous gill rakers (e.g., Benthochromis tricoti).
Piscivores
utilize several, and sometimes odd, feeding behaviors that
depends on the prey.
This is also based on their size, their environment, and their
body structure.
These
we can group into hunters,
stalkers, suckers, opportunistic fish eaters, egg eaters and
scale feeders. The way they capture their prey is
dependent on their jaw and teeth structure.
Hunters
perform either ambushes (Nimbochromis livingstonii), or
they run after their prey (Dimidiochromis compressiceps).
Stalkers
are usually bottom dwelling species that bury themselves to
ambush their prey. Some of them display very good camouflage
(turbots, family Scophthalmidae), or they may have
wormlike appendages on their heads or near their mouths to
attract their prey (Stargazers and Anglers). Some of them,
though, live under fish schools and stalk them from
underneath.
The
nurse shark Ginglymostoma cirratum, for instance, sucks
its prey from holes and cavities, in contrast to other shark
species that hunt and capture their prey.
Opportunistic
piscivores can be any fish that are able to capture and
consume another fish, especially if the prey is younger,
smaller, weaker, or ill. These species are observed to prey on
other fish mostly during seasonal changes of physicochemical
parameters (e.g., lighting)
or during breeding times (Cyphotilapia frontosa).
The
egg eaters have no specialized techniques, and most of them
feed on eggs only occasionally, although some species will
seek other fishes’ nests for eggs (Telmatocromis spp.)
to feed on.
The
scale eaters (e.g., Plecodus straeleni, a Lake
Tanganyika cichlid) have teeth and body shape that enable them
to attack and remove scales from other fishes. They are rarely
kept in home aquaria for this very reason.
The
truth is that they do not, most of the time, severely harm the
attacked individuals in the wild.
Herbivores
usually feed on underwater vegetation consisting of plant
plankton, micro and
macro algae, as well as detritus.
There
are phytoplanktivores
that also pick, suck, or filter plankton.
The
algae eaters scrape,
comb, nibble, or scoop
algae from the surfaces on which algae grows, while the ones
that feed on detritus scoop mud methodically for “greens”. The feeding techniques
mentioned above are quite common in the several different
herbivorous species of Tanganyika (e.g., Tropheini,
Eretmodini, etc). There are a few species that consume
the filamentous algae (Epalzeorhynchos siamensis, E.
kalopterus), and they are very useful as tank mates due to
this feeding preference.
Another
source of food in the wild is parasites. These are little
organisms that use fishes as hosts. External parasites are
found on the body surface, under the operculum and inside the
mouth. If there are many of them it is a problem. Some of the
freshwater species of Mochokidae and the marine Labridae
are famous parasite cleaners. Wrasses (Labridae) lack this
behavior as adults except for the Labroides dimidiatus, L.
bicolor, L. pectoralis in the Indian Ocean and Symphodus
melanocercus in the Mediterranean Sea. This same behavior
is also witnessed in some species of shrimps (e.g., Urocaridella
antonbruunii). These species make actual cleaning stations
and have regular visitors. They wait uncomplainingly for their
turn, and while they are being cleaned they offer wide opened
mouths and gill covers. Parasite feeders are also useful in
tanks because they control the population of external
parasites.
Omnivores
are either opportunistic feeders or scavengers (Anguillidae),
and they can consume whatever they find, from corpses to
terrestrial trees’ fruits, depending on seasonal
availability (Acanthophthalmus kuhli). There are some
species that it seems feed on feces (Scatophagus argus).
These species can be fed on every single food item they find. Even aquatic birds and reptiles (commonly terrapins and sea
turtles) have been found in omnivorous fishes’ stomachs. In
the bigger species’ stomachs there have been found pieces of
boats or even oil barrels. These fishes may not be omnivorous,
but their enormous size helps them to consume nearly
everything. This makes large specimens, or fishes that grow a
lot, difficult tank mates.
Following
this introduction we can now understand which way our fishes
must be fed in captivity to feel like home. Also, it gives us
a clue for the equipment and the suitable aquascaping needed
for their housing. And as long as feeding produces wastes that
we must get rid of, we have to know the type and capacities of
filters that are the optimum for this task. We can also
conclude that their dietary needs are critical for their
health and behavior. But as long as different proteins and
amino acids exist in these different foods, I am led to the
inference that it would cause problems sooner or later. Even
if no obvious health problems could be detected (very
unlilkely), surely some behavior problems may occur. All of us
have noticed unexplained deaths and strange behaviors in our
tanks.
When
we keep some particular species, we want these species
displayed in our tanks the same way as if they were living in
the wild. There is no need to mention the health problems that
can be caused when we attempt to feed herbivores with
mammalian, or even nonherbal proteins. “Malawi bloat” and
“Tropheus disease” are very well known problems. Improper feeding is also considered as guilty of causing
“dropsy” as well.
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| Picture |
Cichlid
species |
Group |
Food |
Adaptations |
Reference |
Photo: A. Konings |
Maylandia
crabro |
Mbuna
flock |
Fish
lice, and other foods |
Behavior:
Facultative cleaner of Argulus (parasitic
crustaceans) from large Bagrus catfish. Also eats
other, varied foods including Bagrus eggs.
Coloration: Distinctive "bumblebee" colors may
advertise cleaning service. |
Ribbink
& Lewis (1982)
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Genyochromis
mento |
Mbuna
flock |
Cichlid
fins & scales |
Behavior:
Skulks close to Mbuna, bites pieces from caudal or anal
fin; sometimes rasps scales from flanks or caudal
peduncle.
Coloration: Polymorphic, morph shown is inconspicuous,
other morphs thought to mimic locally common prey
species.
Anatomy: Broad, strong lower jaw with stout, sharp
bicuspid teeth. |
Ribbink
et al. (1983)
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Nimbochromis
livingstonii |
"Hap"
flock |
Ambush
predator of small fish |
Behavior:
Feigns death, lying motionless on its side.
Coloration: Mimics a rotting fish, luring small fish
within range. |
Fryer
& Iles (1972)
McKaye
(1981) |
From the "trophic
adaptation" table prepared by Dr. Michael K. Oliver.
The full table can be seen at
http://www.malawicichlids.com/mw01100.htm
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Getting
some basics of biochemistry is essential if we are to
understand why feeding the right food is really important. Of
course, it will be a simplified approach, since the task is to
learn something, not get a PhD on it. We all know that DNA is
the genetic material of most living organisms (some viruses
excluded). We all know that DNA is located in the nucleus of
the cell and is responsible for us being humans, or making an Aulonocara
species different from a Nimbochromis species. We
can see that the differences between these two species are
many and important. They differ in their feeding, breeding and
even swimming habits. They also differ in size, temperament,
color and shape. Although environmental conditions may play a
role on how they look (a fish living in a nutrient-poor
environment will never reach its “programmed” final size),
still the major factor determining all that is the DNA. This
is something that has become known to almost everybody. What
most of us do not know is that DNA has only one function –
keeping the codes for the production of proteins.
So
actually, the fish will look as it looks only because it is
producing the specific set of proteins encoded by its DNA. So
far, so good. Well, proteins are formed by small molecules
linked together, the amino acids. If we are to visualize a
protein as a wall, then the amino acids are the bricks. Every
protein is a chain of specific amino acids in a strictly
specified sequence. A DNA molecule is also a chain of specific
bases in a specified sequence. Since the protein comes from
the DNA then there must be a transcription code. Well, there
is. Every three bases of the DNA chain code for one specific
amino acid. When the DNA is “read”, the cell adds one
amino acid for every trio of bases read. Depending on the
number of amino acids added, the resulting product is called
an oligopeptide (small number of amino acids), a polypeptide
or finally a protein (which may contain thousands of amino
acids). If a wrong amino acid is added in the protein chain
then the resulting protein may not work or even cause damage
to the organism. This is usually a genetic problem (point
mutation, which means the wrong base was present in the DNA)
or a problem of the transcription of the DNA. No matter what,
nutrition has nothing to do with it.
However,
if an amino acid is not found in the cell (as a result of
malnutrition), then the peptide or protein will not be
produced by the cell. The impact this may have on our fishes
is obvious. You see, among other things, enzymes and some
hormones are made of amino acids, too! Enzymes are absolutely
essential in almost every chemical reaction that takes place
in our fish (which would be otherwise impossible to take place
at 26oC at a reasonable speed), while hormones
control some very important aspects such as size and growth,
sexual activity, maturation, etc. Enzymes are also essential
to utilize hydrocarbons and lipids (the other elements in food
besides proteins) during digestion. In short, without enzymes
and hormones every reaction in the fish would stop.
So
amino acids are the bricks every organism is made of. The
amino acids are further classified as essential and
non-essential. The essential ones are those that the organism
(our fish in this case) can’t produce by itself and relies
on its food for. The non-essential ones are those that the
fish can build by itself. So, the essential amino acids must
be found in order to survive. When fish take their food, it
contains proteins, which are broken down (catabolism) to amino
acids that are used to make its own proteins (anabolism).
Schematically, the fish breaks down the wall, selects which
bricks it needs and then throws away the rest (in the form of
wastes). Since every protein contains different amino acids,
if the fish doesn’t get the correct proteins, it will not
get the essential amino acids it needs which – remember –
it can’t synthesize by itself. During millions of years of
evolution, fish species have adapted in specific environments
that can supply them with the proteins they need. Insectivores
eat insects because only insects contain the right proteins
for them.
Feeding
them spirulina pellets in our tank will not give them the
proteins they need. They will eat it because they are hungry,
but some amino acids will not be there. Their intestinal
tract, as well as their whole body, is specially designed to
absorb and use this kind of proteins, not just any protein. As time passes by, the fish will develop a
“shortage” in one or more of the essential amino acids and
– sooner or later – will die. Unfortunately, there are no
“alternative biochemical pathways” since this would be a
tremendous waste of energy, and nature hates that. Herbivores
have a longer intestine with special mucosa and a batch of
enzymes to utilize vegetable matter. Feeding them beef heart
will shortly kill them. Feeding herbivores or insectivores
with foods that contain too much fat (especially animal fat)
will also cause very serious health problems. Their peptic
system will not work normally in the presence of all this fat
simply because it was not designed to. An organism can’t
simply adapt to the foodstuff we give it in a month or a year.
It takes thousands (even millions) of years to adapt to such a
change. Please remember that many species have been extinct
simply because a specific food source was eliminated from
their environment. In extreme cases, they became extinct
because only one element was depleted from their surroundings.
Amino
acids and peptides were used for this analysis only because
proteins, hormones and enzymes are the chemical names most
hobbyists are familiar with. However food consists of three
equally important groups of substances: proteins, fat (fatty
acids, saturated or not) and carbohydrates (e.g. sugars).
Proteins are used for “building” or “repair” purposes,
carbohydrates are the main source of energy while fatty acids
are used for many purposes (energy storage being one of them).
The
same facts that apply for the proteins apply for fatty acids
and carbohydrates. Fish (as every other living organism) can
utilize specific fatty acids and carbohydrates (you guessed
right; there are many of them). Moreover, their daily needs
call for a specific mixture of the correct elements. Thus, you
can’t feed your fish a diet based exclusively on
carbohydrates since it will soon develop symptoms of severe
malnutrition. The same will happen if you feed it
carbohydrates that it can’t metabolize effectively (or at
all).
What
should we do then? There are some general rules that, if
followed, will ensure well-fed fish with minimum problems.
Try
never to overfeed because fishes in the wild are not always
full. It is not so easy to be fed on a regular basis if you
have to live in a hostile environment while trying to grow,
not to be eaten and later increase the population of your own
kind. Also, natural environments are usually oligotrophic,
meaning there is not as much food as we may think there is.
So, nutrients are available in very low concentrations or are
totally absent. This forces the fish to make the best use of
any available sources and may lead to further adaptation.
Indeed, it is well known that that the so called "Competitive
Exclusion Principle" is applied in every biotope
known to man, Rift Lakes included. According to this, two (or
more) species can't feed on the same food, in the same way, at
the same place and time. If they were, one of them, the
fittest would survive at the expense of the less fittest
(survival of the fittest). Therefore it becomes apparent that
two (or more) species feeding on the same food should in fact
be feeding on only a very particular subset of the total
available food.
Thus,
it has been shown that although many mbuna species may be
feeding on the algae found on the same rocks, in the same
area, their special trophic adaptation allows them to eat
different parts of it (upper layer, algae found in crevices
etc). Moreover fish know which species compete directly with
them for the same subset of food and direct their aggression
to those species only. Of course, the first candidate is their
own species which partly justifies the intraspecies aggression
of most mbuna, even against their own females.
This
was also demonstrated by a recent study which showed how
fourteen species of Lake Tanganyika cichlids feed on the
thirteen species of shrimp found in the Lake. It was shown
(among others) that within the same shrimp population, larger
cichlids prayed on larger shrimps while smaller fish were
capable of eating the smaller shrimps which evaded the larger
cichlids easier.
It
is evident that in nature food is not everywhere, not all the
time. Fish have developed special skills in order to
effectively use the sources available. This means that they
are not fed "2-3" times daily and their bellies are
not always full. Please remember that the fish we keep in our
tanks are built to cope with this kind of environment. Feeding
them sparingly, or even every other day may seem cruel but it
is the best approach. If we test our fishes’ native waters
we shall find no nitrates and no phosphates such as we can
measure in our tanks. It is more important for keeping fishes
healthy if the water (environment) is clean and clear, than
how much we feed, as long as the “best qualified” foods
are provided.
Only
fry and semi-adult fishes need more than one feeding per day.
We feed adults more heavily only during breeding. But we give
foods with minimal fats because we do not want delivery
problems for the females from fats accumulated around their
vents.
Try
to feed the right food, not just any food your pet shop
carries. Herbivores need special food, as do all the other
feeding categories listed at the beginning of this article.
“All around” foods are a compromise and should be used
alternatively with specialized foods.
If
we research fish biology more thoroughly, we shall find out
that many “life styles”, foods, and behaviors are present
in the underwater world. Feeding fishes is not just shopping
at our local pet store. We hope that the data presented in
this article make this very clear to every hobbyist.
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MCH
Literature:
Ronald Coleman. Food for Thought, in
"Cichlids and Science", Cichlid News, 9(3): 32-34,
2000
Ronald Coleman. Feeding Frenzy, in
"Cichlid and Science", Cichlid News, 10(1): 32-34,
2001
Note : You can find the complete table prepared by Dr. Michael K. Oliver
at
http://www.malawicichlids.com/mw01100.htm
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