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An Introduction to Cichlids
 
       
Astronotus_ocellatus
Scientific classification
     
Kingdom : Animalia
Phylum : Chordata
Class : Actinopterygii
Order : Perciformes
Suborder : Labroidei
Family : Cichlidae
     
Subfamilies
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

 

 

 

 

 

 

Introduction

Cichlids are a large group of fish which are very popular in both aquarium community as well as food industry.

They are placed in family Cichlidae.
A full taxonomic classification is given in the sidebar.

This family is both large and diverse.
At least 1,300 species have been scientifically described, making it one of the largest vertebrate families.
New species are discovered annually, and many species remain un described.
The actual number of species is therefore unknown, with estimates varying between 1,300 and 3,000.
 
Physical Description
Cichlids span a wide range of body sizes, from species as small as 1 inch belonging to genus apistogramma to much larger species approaching 36 inches belonging to genus Boulengerochromis .

Cichlids exhibit a great diversity of body shapes, ranging from strongly laterally compressed fish belonging to genus like Altolamprologus, Pterophyllum , and Symphysodon to fish that are cylindrical and highly elongate like those belonging to genus Julidochromis, Teleogramma, Teleocichla etc.

Generally, however, cichlids tend to be of medium size, ovate in shape and slightly laterally compressed, and generally similar to the North American sunfishes in morphology, behavior, and ecology.

The family also includes many familiar aquarium fish, including the angelfish, oscars, discus, a broad group called "africans".
Cichlids have the largest number of endangered species among vertebrate families, most in the haplochromine group.
Cichlids are particularly well known for having evolved rapidly into a large number of closely related but morphologically diverse species within large african lakes, particularly Tanganyika, Victoria, Malawi, and Edward.
Their diversity in the African Great Lakes is important for the study of speciation in evolution. Many cichlids that have been introduced into waters outside of their natural range have become nuisances, such as tilapia in the USA and India.

Anatomy and appearance

Cichlids share a single key trait: the fusion of the lower pharyngeal bones into a single tooth-bearing structure.
A complex set of muscles allows the upper and lower pharyngeal bones to be used as a second set of jaws for processing food, allowing a division of labor between the "true jaws" (mandibles) and the "pharyngeal jaws".
Cichlids are efficient feeders that capture and process a very wide variety of food items.
This is assumed to be one reason why they are so diverse.

Cichlids vary in body shape, ranging from compressed and disc-shaped (such as Symphysodon) , to triangular (such as Pterophyllum), to elongate and cylindrical (such as Crenicichla).

The features that distinguish them from the other fish are:

  • A nostril on each side of head.
  • The lateral line is interrupted in most species.
  • Scales in lateral lines may be over 100, usually 20-50.
  • Dorsal fin usually have 7-25 spines and 5-30 soft rays.
  • Spines in anal fin 3-15 (generally 3);
  • Soft rays 4-15 (a few with 30).
  • Sub ocular shelf absent.
  • A distinctively shaped otolith.
  • The small intestine's left-side exit from the stomach instead of its right side as in other fish.

Taxonomy

The family Cichlidae was first described by Heckel (1840), based on the Natterer collection from Brazil (illustrations in Riedl-Dorn, 2000).
Another early major classification is by Jardine (1843), based on the Schomburgk collection from Guyana, Brazil and Venezuela (Kullander & Stawikowski, 1997a-b, for identifications).
Steindachner (1875) worked on the Thayer expedition collection of Amazonian cichlids, but did not add much beyond the work of Heckel.
Günther (1868, based on several shorter papers) described and illustrated a large part of the Central American cichlid fauna, followed by Regan (1906-1908). Pellegrin (1904) revised the family with diagnoses of all genera and species known to him.
Much of Pellegrin’s efforts with the Neo tropical taxa were improved upon by Regan’s series of generic revisions in the next two years (Regan, 1905-1906), which remained the platform for all Neo tropical cichlid systematics until the 1980s

The first modern phylogenetic revision of the Neo tropical cichlids was presented by Cichocki (1976), and most recently Kullander (1988) and Farias et al. (1999) have provided phylogenetic hypotheses based on morphology and molecular data respectively.
A formal classification down to tribe is provided by Kullander (1988).
Scientific general reviews of the family are provided by Keenleyside (1991) and Barlow (2000).

Kullander (1998) recognizes eight subfamilies of cichlids:

Comparisons between a morphologically-based phylogeny and analyses of gene loci produce differences at the genus level.
There remains a consensus that the Cichlidae as a family is monophyletic (descended from a common ancestor).

One problem that transformed cichlid taxonomy is related to dentition, which had been used as a classifying characteristic. In many cichlids, tooth shape changes with age, due to wear, and cannot be relied upon. Genome sequencing and other technologies transformed cichlid taxonomy.

Range and habitat

Cichlids are the most species-rich non-Ostariophysan family in freshwaters worldwide.
They are most diverse in Africa and South America.
It is estimated that Africa alone hosts at least 1,600 species.
Central America offers approximately 120 species, as far north as the Rio Grande in southern Texas.
Madagascar has its own distinctive species, only distantly related to those on the African mainland.

Endemic cichlids are largely absent in Asia, except for four species in the Jordan Valley in the Middle East, one in Iran, and three in India and Sri Lanka.

Cichlids are less commonly found in brackish and saltwater habitats, though many species tolerate brackish water for extended periods;
Cichlasoma urophthalmus, for example, is equally at home in freshwater marshes and mangrove swamps, and lives and breeds in saltwater environments such as the mangrove belts around barrier islands.

Several species of Tilapia, Sarotherodon, and Oreochromis are euryhaline( can tolerate water with high salinity) and can disperse along brackish coastlines between rivers.

Only a few cichlids, however, inhabit primarily brackish or salt water, most notably Etroplus maculatus, Etroplus suratensis, and Sarotherodon melanotheron.
Cichlids have not reached any oceanic island and have a predominantly Gondwanan distribution, showing the precise sister relationships predicted by vicariance: Africa-South America and India-Madagascar.

Feeding

Cichlids exhibit a wide range of feeding strategies and adaptations.
Some are primarily herbivores feeding on algae (e.g. Petrochromis) and plants (e.g. Etroplus suratensis).
Small animals, particularly invertebrates, are only a minor part of their diet.
Other cichlids are detritivores and eat all types of organic material; among these species are the tilapiines of the genera Oreochromis, Sarotherodon, and Tilapia.
Other cichlids are predatory and eat little or no plant matter.
These include generalists that catch a variety of small animals, including other fishes and insect larvae (e.g. Pterophyllum), as well as variety of specialists.

Trematocranus is a specialized snail-eater, while Pungu maclareni feeds on sponges.
A number of cichlids feed on other fish, either entirely or in part.
Crenicichla are stealth-predators that lunge from concealment at passing small fish, while Rhamphochromis are open water pursuit predators that chase down their prey.

Paedophagous cichlids such as the Caprichromis species eat other species' eggs or young, in some cases ramming the heads of mouth brooding species to force them to disgorge their young

Among the more unusual feeding strategies are those of Corematodus, Docimodus evelynae, Plecodus, Perissodus, and Genyochromis spp., which feed on scales and fins of other fishes, a behavior known as lepidophagy, along with the death-mimicking behavior of Nimbochromis and Parachromis species, which lay motionless, luring small fish to their side prior to ambush.

This variety of feeding styles has helped cichlids to inhabit similarly varied habitats. Its pharyngeal teeth (teeth in the throat) afford cichlids so many "niche" feeding strategies, because the jaws pick and hold food, while the pharyngeal teeth crush the prey

 

Reproduction-Mating

Like most fish cichlids lay eggs and young emerge from the eggs.
Mating behaviors of cichlids is both monogamous as well as polygamous.
The mating system of a given cichlid species is not consistently associated with its brooding system.
For example, although most monogamous cichlids are not mouth brooders, Chromidotilapia, Gymnogeophagus, Spathodus and Tanganicodus are all monogamous mouth brooders.
In contrast, numerous open or cave spawning cichlids are polygamous; examples include Apistogramma, Lamprologus, Nannacara and Pelvicachromis.

Brood care

All cichlid species show some form of parental care for both eggs and larvae, often nurturing free-swimming young until they are weeks or months old.

Communal parental care, where multiple monogamous pairs care for a mixed school of young have also been observed in multiple cichlid species, including Amphilophus citrinellus, Etroplus suratensis, and Tilapia rendalli.

Comparably, the fry of Neolamprologus brichardi, a species that commonly lives in large groups, are protected not only by the adults, but also by older juveniles from previous spawns.

Several cichlids, including discus (Symphysodon spp.), some Amphilophus species, Etroplus and Uaru species feed their young with a skin secretion from mucous glands.

Parental care falls into one of four categories:

  • Substrate or open brooders,
  • Secretive cave brooders (also known as guarding speleophils
  • Ovophile mouth brooders
  • Larvophile mouth brooders.

Substrate/Open brooding

Open or substrate brooding cichlids lay their eggs in the open, on rocks, leaves, or logs.
Examples of open brooding cichlids include Pterophyllum, Symphysodon spp, and Anomalochromis thomasi.
Male and female parents usually engage in differing brooding roles.
Most commonly, the male patrols the pair's territory and repels intruders, while females fan water over the eggs, removing the infertile and leading the fry while foraging.
However, both sexes are able to perform the full range of parenting behaviors.

Cave brooding

Secretive cave spawning cichlids lay their eggs in caves, crevices, holes, or discarded mollusc shells, frequently attaching the eggs to the roof of the chamber. Examples include Pelvicachromis spp., Archocentrus spp, and Apistogramma spp.

Free-swimming fry and parents communicate in captivity and in the wild. Frequently this communication is based on body movements, such as shaking and pelvic fin flicking.
In addition, open and cave brooding parents assist in finding food resources for their fry.
Multiple neo tropical cichlid species perform leaf-turning and fin-digging behaviors.

Ovophile mouth brooding

Ovophile mouth brooders incubate their eggs in their mouths as soon as they are laid, and frequently mouth brood free-swimming fry for several weeks. Examples include many Great Rift Valley lake cichlids(Lake Malawi, Lake Tanganyika and Lake Victoria) endemics, e.g.: Maylandia, Pseudotropheus, and Tropheus, along with some South American cichlids such as Geophagus steindachneri.

Larvophile mouth brooding

Larvophile mouth brooders lay eggs in the open or in a cave and take the hatched larvae into the mouth.
Examples include some variants of Geophagus altifrons, and some Aequidens, Gymnogeophagus, and Satanoperca.
Mouth brooders, whether of eggs or larvae, are predominantly females.

Exceptions that also involve the males include eretmodine cichlids (genera Spathodus, Eretmodus, and Tanganicodus), some Sarotherodon species, Chromidotilapia guntheri, and some Aequidens species.

 

 

 

Author/Credits

 

  Sandeep Raghuvanshi
Picture Credits   Wikipdeia and other sources which have releases under GNU, unless specifically credited
CITATIONS/FURTHER READING   Kullander, S. O., 1998. A phylogeny and classification of the South American Cichlidae (Teleostei: Perciformes). p. 461-498. In L.R. Malabarba, R.E. Reis, R.P. Vari, Z.M. Lucena and C.A.S. Lucena (eds.) Phylogeny and classification of neo tropical fishes. Porto Alegre, Edipucrs. 603 p.
    Froese, R. and D. Pauly. Editors. 2011.FishBase. World Wide Web electronic publication. www.fishbase.org, ( 10/2013 )