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.
| The Suborder Labroidei |
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| A clownfish; family Pomacentridae |
A surfperch; family Embiotocidae |
A cichlid; family Cichlidae |
A wrasse; family Labridae |
Global diversity of cichlids
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, because 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 eggs
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.
