How do the cichlids fit
into the 25,000 species of living fishes? In a nutshell, living fishes
can be broken down into 5 classes, the largest of which is called the
Actinopterygii, or bony-finned fishes. Other classes include things
like hagfish (Class Myxini) and sharks (Class Chondrichthyes). Humans
and all other land vertebrates are actually fishes falling into Class
Sarcopterygii, or lobe-finned fishes, though we don't usually include
the numbers of land vertebrates in the count of fishes.
Of the 57 orders of
fishes, 42 of these are Actinopterygians. These include all sorts of
fishes including sturgeons and gars, eels, herrings, minnows, catfish,
pike, smelt, salmon, cod, anglerfish, livebearers, sculpins,
perch-like fish and flatfish. This is a huge group of organisms
comprising over 23,000 species.
Within this bounty of
diversity there is one order that has exceeded all others in
generating new and different forms, and this is the order Perciformes,
or perch-like fishes. The perciform fishes (Order #55 according to
Nelson 1994) contains 148 families in almost 1500 genera, encompassing
almost 10,000 species.
One of those families is
the Cichlidae. The cichlids make up a disproportionate number of the
Perciform fishes, ranking second in number only to the gobies (Gobiidae).
Other large families of perciform fishes include the wrasses (Labridae),
sea basses (Serranidae), blennies (Blenniidae), damselfishes (Pomacentridae),
drums and croakers (Sciaenidae) and cardinalfishes (Apogonidae) all of
which have more than 200 species apiece.
Ichthyologists do not yet
fully understand all the complex relationships within the Perciformes;
however, it seems relatively certain that the Cichlidae belong in a
cluster of closely related families which includes the wrasses (Labridae),
the damselfishes (Pomacentridae) and the surfperches (Embiotocidae).
This cluster is called the suborder Labrodei.
Cichlids come in a
surprising diversity of shapes, sizes and colours. They share a few
common characteristics, including life in freshwater and advanced
forms of parental care of their young. These characteristics do not
define the cichlids, in that many other fishes also have these
characteristics and yet are not cichlids, but they do explain part of
the immense popularity of these fishes for aquarists.
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Cichlids are found in
the New World and the Old World
Geographic Distribution
--
Cichlids are found in the New World from southern Texas down to
Argentina in South America. They are found throughout Africa and parts
of the Middle East. There are cichlids on the Island of Madagascar, on
the Island of Sri Lanka, and along the southern coast of India. There
are no cichlids native to the Far East or Australia, nor are any found
naturally in North America north of Texas. However, cichlids,
particularly the genus Tilapia, have been introduced either
deliberately or accidentally into many locations around the world
where they were not found natively. For instance, there are many
introduced cichlids in the waterways and canals of southern Florida.
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Paratilapia polleni
male, a Madagascan cichlid
In the aquarium hobby,
cichlids are often classified as either "New World" or
"African". I think this does a great disservice because the
differences between various New World cichlids are as great as the
differences between New World and African cichlids. Similarly, many
African cichlids are radically different from other African cichlids
and a beginner might easily be misled into thinking that just because
a cichlid comes from Africa tells you something about how it lives,
what it eats, how to keep it in an aquarium, etc. This is simply not
true.
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The Rio Puerto Viejo, in
Costa Rica
Habitat Distribution
-- Cichlids are found
in almost every possible body of freshwater within their geographic
range including rivers and lakes, swamps and even ditches and puddles.
They are not found at high elevations and generally require water
warmer than about 68oF (20oC).
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A peacock bass, Cichla
ocellaris
Diversity of Size and
Form --
There are large predatory cichlids like the peacock bass (Cichla
ocellarus) of South America and there are tiny secretive cichlids
(often called "dwarfs") found in many places, including the
kribensis group from West Africa (e.g., Pelvicachromis pulcher)
and the genus Apistogramma from South America. There are
herbivores (plant-eaters) like the mbuna of Lake Malawi and there are
carnivores, like the slender pike-cichlids of the Amazon.
Diversity of Parental
Care
-- All cichlids
provide parental care in one form or another. This is not the norm for
fishes -- most fish species do not provide parental care, and of those
that do, it is typically the male that provides the parental care (in
contrast to mammals or birds where the female is often the primary
care-giver). But in cichlids, almost anything can and does happen and
that is one of the most fascinating aspects of their biology.
Some species are substrate-spawners,
meaning that they lay their eggs on the ground or on a hard surface
like the leaf of a plant or on a log. Parental care then consists of guarding
the eggs, fanning them to provide oxygenated water, then caring
for the hatchlings (called wrigglers) which eventually become
free swimming fry. Cichlids are often devoted parents and the
length of parental care may extend for weeks or even months.
Most substrate spawners
are biparental, meaning both parents take care of the kids, though
their exact roles may vary (this is one of the topics I do research
on). A few are uniparental with only one parent taking care of the
kids.
Some cichlids are haremic
(e.g., some of the Apistogramma) were each female lays her eggs
in her own cave in the territory of a male, but there may be several
females within this male's territory. Each female provides care for
her own young, whereas the male protects the entire territory from
other males and predators.
There is an interesting
variation on substrate spawning seen particularly in Lake Tanganyika
-- the shell dwellers. Shell dwellers lay their eggs in the confines
of an unused snail shell. This affords great protection to the
offspring because a parent can sit in the mouth of the shell and block
any predators. Sometimes the shell is so small that only the female
can get into it and the male remains permanently outside on patrol. In
such cases the male may be much larger than the female and may have
many females in his territory, each with her own shell.
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Tilapia esculentas
female holding egg
Many species of cichlids,
particularly those in Lake Malawi and Lake Victoria, and some in Lake
Tanganyika are mouthbrooders. Mouthbrooding is amazing. It is
not restricted to cichlids (a number of other families have evolved it
independently), but it is nonetheless an incredible thing to see. In
these species, a female lays her eggs but rather than sticking them to
the substrate, she picks them up in her mouth. The male fertilizes
them in her mouth and the eggs remain there, sometimes to hatching,
and sometimes well-beyond.
Mouthbrooding is not only
found in females in cichlids. Some species are female mouthbrooders,
others are biparental mouthbrooders and a few are male mouthbrooders.
Even within the
mouthbrooders, there are different types. In some South American
species, there is a mixture of substrate spawning and mouthbrooding.
We call these delayed mouthbrooders: they lay the eggs on the
substrate, guard them for a while, and then pick up the young and
mouthbrood them. To distinguish delayed mouthbrooders from species
which pick up the eggs right after spawning, we call the latter immediate
mouthbrooders.
There are no live-bearing
cichlids, though there are a number of other fish families which give
birth to live young.
A
cichlid [pronounced sick-lid] is a fish in the Family Cichlidae. This
is an immense family of fishes of almost unbelievable diversity.
Conservative estimates of the number of species of cichlids range from
1300 to many, many more. Many people have seen a cichlid without even
knowing it: oscars and freshwater angelfish, both common aquarium
fish, are cichlids.