Diversity The Cichlidae family stands out as an extraordinary example of vertebrate evolution. From the sheer size of the family to the complexity of their ecological interactions and rapid evolution, cichlids provide a unique glimpse of the many factors that promote speciation. The behavioral and physical changes resulting from intense speciation in cichlids is equally impressive. Cichlids demonstrate some of the most unique and intensive parenting in fishes and utilize several different mating systems, from monogamy to polygynandry (See Reproduction). Many feeding behaviors found in cichlids are unique among freshwater fishes (See Behavior and Food Habits). Finally, although the general body plan of cichlids is constant, they come in a dazzling array of shapes, sizes, colors, and dental plans, making them popular with aquarists and aquaculturists (See Physical Description and Economic Importance to Humans). (Berra, 2001; Greenwood and Stiassny, 2002; Moyle and Cech, 2000; Stiassny, 1991; Wheeler, 1985) There are no concrete figures on the number of genera and species in the Cichlidae family because there are still many revisions being made and a considerable number of species are yet to be described. Rough estimates range from 200 to 2000 species and approximately 140 genera, which, after Cyprinidae and Gobiidae, would make them the third largest family of bony fishes. The largest genus is the African Crenicichla with over 100 species. Cichlids inhabit fresh waters, and many species are endemic to isolated lake environments. The fact that no genera occur on more than one continent illustrates the degree of endemism in this family. (Berra, 2001; Nelson, 1994)

Development Cichlids follow a typical developmental pattern but some species brood the eggs in the mouth while developing. Parents exhibit various behaviors to promote the growth of young, which develop through three distinct stages: eggs, wrigglers (newly hatched, non-free-swimming young), and fry (free swimming but dependent on the parent). At the early stages of development, parents fan the eggs to provide ventilation and remove waste (termed “fanning”). Some species use their mouths to suck away wastes or to remove dead or fungus-ridden eggs (termed “mouthing”). Mouthbrooding species that carry developing eggs in the buccal cavity (mouth) accomplish mouthing and fanning by rolling and swishing the eggs in the mouth (termed “churning”). Finally, several behaviors are related to aiding the young in feeding. Parents may pick up leaf matter and drop it near the young so they may forage on the unexposed side (termed “leaf-lifting”), or dig into the substrate with the fins to expose buried prey (termed “findigging”). Another unusual method of aiding the fry in development is “micronipping,” in which fry feed on mucous secreted from the skin of parents. Micronipping was first discovered in Symphysodon discus, but has since been recorded for several other cichlid species. (Keenleyside, 1991) Some species of blue tilapia (among others), which are widely used in aquaculture, are susceptible to sex change for a period approximately 30-40 days after hatching by controlling temperature or adding hormones (See Mating Systems). Despite the fact that genetics also influence sex determination, hormones and temperature can overrule genetic determination, creating offspring that are all one sex. Aquaculturists take advantage of this fact to create single sex tanks, thus avoiding overpopulation. (Barlow, 2000) Development - Life Cycle

temperature sex determination

Lifespan/Longevity The lifespan of many wild cichlids is unknown. However, in aquaria they are relatively long-lived, about 10 years on average. Several can reach up to 18 years in captivity, suggesting that at least some cichlids have considerably long lifespans. (Barlow, 2000)

Behavior As a family, cichlids display numerous complex behaviors in feeding, reproduction (see Reproduction: Mating Systems), and parental care (Reproduction: Parental Care). In an evolutionary sense, the exploratory behavior of cichlids is also very important because this is what initially encouraged and later refined speciation. For example, competition for finite food sources in isolated ancient lakes encouraged individuals to exploit formerly unavailable food sources. Eventually morphological changes followed and feeding behaviors improved the capacity to exploit the new food sources. As a result, in some habitats, such as the Great Lakes of East Africa, cichlids fill virtually every ecological role within their trophic level (see Food Habits and Ecosystem Roles). In addition to breeding territories, investigators have learned that many cichlids maintain feeding territories as well. With regard to territorial feeding behavior cichlids are unique; very few freshwater fishes defend feeding areas, and these few usually only maintain the territories for brief periods. One hypothesis explains cichlids’ behavioral departure with three possible factors: the long-term stability of the environment (ancient lakes) in which many cichlids live, diverse feeding habits—some of which are similar to territorial marine reef species, and the fact that cichlids initially inhabited marine environments as opposed to archetypal freshwater fishes, such as minnows, catfishes and their relatives. (Barlow, 2000) The intensity of territoriality in cichlids ranges from extreme aggression - the exclusion of all other fishes, to the maintenance of brief territories during spawning, to no territories at all. Feeding territories are often better defined than breeding territories, with males of the same species (conspecifics) overlapping little. However, in some cases the feeding territories of different species (heterospecifics) do overlap. For instance, Pseudotropheus elongatus of Lake Malawi aggressively defends a territory to promote the growth of ‘algal gardens,’ which are maintained by females and juveniles. Females leave the territory to spawn but return with the eggs (mouthbrooding) seeking food and protection within the territory. However, the territory of Petrotilapia tridentiger (22 m2 on average) may actually include several Pseudotropheus elongatus territories as well as the territories of a few other small heterospecifics. Petrotilapia tridentiger defends against conspecifics and dominates the social hierarchy within its territory, feeding exclusively on the algal gardens of Pseudotropheus elongatus (which contain 2.25 times more algae than surrounding areas). Territorial fishes may also be overcome by large schools that use numbers to overwhelm aggressive defense with numbers. Petrochromis fasciolatus of Lake Tanganyika may form columns of 40 to 150 individuals and specifically attack the feeding territories of Variabilichromis moorii. The reason for selectively targeting the territory of Variabilichromis moorii is that algal density can be up to 15 times higher than in non-defended areas. A slightly different system is found in Gnathochromis pfefferi from Lake Malawi. Gnathochromis pfefferi females are not territorial but have overlapping home ranges with males. Males defend their feeding territories in the afternoon and overnight but during the day, they migrate to breeding territories where they spawn with females. (Barlow, 2000; Ribbink, 1991) Key Behaviors

natatorial

diurnal

nocturnal

parasite

motile

nomadic

territorial

social

colonial

dominance hierarchies

Communication and Perception Cichlids are able to communicate by various means: visual, acoustic, chemical and tactile. Visual communication primarily involves color changes and body movements and gestures. At least some cichlids are able to discern colors. Color changes are important in identifying individuals or families, or for communicating aggression, dominance, or sexual state. Typically, the brightest color patterns are associated with aggression. Body movements and gestures are also used to communicate aggression, dominance, or sexual state, and often combine with swimming patterns and color changes to emphasize a particular display. Tactile communication is mainly observed in aggressive males, such as the case of “mouth-fighting.” Tropheus moorii males lock mouths until one individual is pushed to the bottom and flees. In some mouthbrooding species (Simochronis and Tropheus) males often touch the anal region of the female as she begins to expel her eggs, presumably encouraging the female to lay her eggs. Sounds, such as grunts, thumps or purrs have been catalogued for at least 16 cichlid species. Experiments with one cichlid, Archocentrus centrarchus, have revealed that recorded sounds (produced during aggressive displays) evoked an aggressive response. Cichlids are known to use chemical cues to recognize their young in parenting. For example, Amatitlania coatepeque and Amphilophus citrinellus are able to discriminate their own small fry from those of other species. The reverse is also true; Amphilophus citrinellus fry are able to distinguish chemical cues given off by their parents. Etroplus maculates and Etroplus suratensis, which feed on fry, use chemical signals to avoid eating fry of the same species. Finally, monogamous pairs of some species need both visual and chemical cues to recognize each other. (Barlow, 2000; Nelissen, 1991) Communication Channels

visual

tactile

acoustic

chemical Other Communication Modes

mimicry

pheromones

scent marks

vibrations Perception Channels

visual

tactile

acoustic

vibrations

chemical

Food Habits As a family, cichlids consume virtually every type of food source available in the freshwater habitat they are found. They exhibit numerous modifications of the lips, teeth, jaws and gill rakers depending on the main food source. Although many cichlids are morphologically adapted to a particular food source, they may become generalists depending on availability. Additionally, cichlids consume various types of food depending on their stage of growth. Herbivorous cichlids may browse, scrape, comb, ‘tap’ or suck epiphytic (attached) algae, unicellular algae, and/or clumps of the substrate. Planktivorous cichlids browse throughout the water column on zooplankton and phytoplankton. Piscivorous cichlids feed on whole fish, the fry, larvae, or eggs of mouthbrooding species, and the scales or fins of various fishes. Three species from the genus Cyrtocara (Lake Malawi) use the peculiar technique, termed head-ramming, of shoving their head into the mouth of female mouthbrooders to force the expulsion of eggs, larvae, or fry, which they eat. Cichlids that feed on aquatic insects and other invertebrates use a variety of methods to expose or capture prey. Several species (Labidochromis maculicauda, Tanganicodus irsacae) browse over patches of algae or substrate, picking out individual insects and crustaceans. Lethrinops (Lake Malawi) feed on chironomid larvae by biting into the sandy substrate and filtering the larvae out with their gill rakers. The enlarged lips of some cichlids are used to suck insects out of cracks and crevices, while in others the lips help to feel for prey when browsing over various substrates. In addition to the latter feeding methods, some cichlids have developed swimming patterns allowing them to sneak up on prey or use larger fish for cover. Finally, the teeth of some cichlids are predominantly molars, allowing them to crush and process small and thin-shelled mollusks. (See an illustration of tooth morphology and diversity in fish). (Yamaoka, 1991) Primary Diet

carnivore piscivore eats eggs eats body fluids eats non-insect arthropods molluscivore scavenger

herbivore

omnivore

planktivore

detritivore Foraging Behavior

filter-feeding

Predation Many large cichlids prey on smaller members of their family or specifically feed in eggs, larvae, or fry. Investigators have also observed newly independent juveniles preying on young of the same or related species. These predation pressure help explain the evolution of intense parental care in cichlids. Introduced species, such as Nile perch, have proven disastrous for many endemic cichlids, even causing the extinction of some species (See Ecosystem Roles and Conservation Status). Humans have also exploited cichlids throughout their range for centuries. (Greenwood and Stiassny, 2002) Anti-predator Adaptations

mimic

cryptic Known Predators fish (Actinopterygii) humans (Homo sapiens)



Ecosystem Roles In the Great Lakes of Africa, the number of cichlid species is so large they fill virtually every ecological role within their trophic level, with the exception of primary producers such as photosynthetic algae and benthic arthropods. As one might expect, there is considerable interplay between various cichlid species in terms of predation and food availability. However, cichlids also influence the species of plants and algae that grow in their habitat (top-down control). One example of top-down control is illustrated by the introduction of the piscivorous Nile perch into Lake Victoria. The Nile perch is a voracious predator of small, planktivorous cichlids, which suffered precipitous population decline after the perches’ introduction. Planktivorous cichlids exert considerable predation pressure on zooplankton, and after they were eliminated, the zooplankton community changed drastically, to the point that a new species of zooplankton began invading the lake, Daphnia magna. (Berra, 2001; Jonna and Lehman, 2002) Ecosystem Impact

biodegradation

keystone species

parasite

Economic Importance for Humans: Positive Several cichlid genera are popular aquarium fishes - Cichlasoma, Pterophyllum, Symphysodon, and jewelfishes - because of their mild temperament and ease of breeding in captivity. However, most cichlids are extremely aggressive when kept in small areas and very difficult to breed. Several Cichla species are popular with sport fishermen, especially in Brazil. Cichlids have also been introduced for recreational fisheries or vegetation control. (Greenwood and Stiassny, 2002; Wheeler, 1985) Some cichlids are used extensively in aquaculture for several reasons. They are a good source of ‘white fish’ and fish products, they lack small bones in the muscle, and some species can grow quite large, allowing for the production of value-added products such as fillets. Most importantly, they feed low on the food chain (aquatic plants and plankton) so the cost of feed is low. Oreochromis and Tilapia are the most extensively farmed cichlids. They are most widely grown in Israel and Asia but cichlid aquaculture has been introduced to many other regions: Egypt (Tilapia), Africa (Oreochromis), Latin America (Astronotus, Cichlasoma and Orechromis), and the Caribbean (Tilapia). (Pullin, 1991) Positive Impacts

pet trade

food

research and education

controls pest population

Economic Importance for Humans: Negative No specific information was found concerning any negative impacts to humans.

Conservation Status Because many cichlid species are endemic to small geographic areas, they can be threatened relatively easily. Many cichlid species will never be described because they are going extinct so quickly. Such is the case with cichlids of Lake Victoria after the introduction of Nile perch. Nile perch were introduced as a food source (unsupervised) but, as a voracious predator, began to destroy cichlid populations throughout the lake. This has resulted in the largest mass extinction of endemic species in recent times. Conservative estimates are that across the Cichlidae family, 43 cichlids are extinct, five are extinct in the wild, 37 species are critically endangered, 11 species are endangered, 34 species are vulnerable, and one species is at low risk. (Berra, 2001; The World Conservation Union, 2002) IUCN Red List [Link] Not Evaluated

The earliest known cichlid fossils were collected in South America, dating back to the Eocene (57 to 37 million years ago), and in Africa, dating back to the Oligocene (33.7 to 23.8 million years ago). However, the fossil history is poor and it is widely believed that the cichlids, along with other labroid families, arose sometime early in the Cretaceous epoch (144 to 66.4 million years ago). Despite the paucity of fossils, investigators have identified several existing Malagasy and Asian genera as the least derived within the Cichlidae. Researchers have gained a good understanding of the evolutionary biology of cichlids from this discovery. For instance, substrate brooding is considered the ancestral breeding system because it is practiced by the oldest genera in Madagascar and Asia. (Greenwood and Stiassny, 2002; Stiassny, 1991)

Contributors R. Jamil Jonna (author), Animal Diversity Web.

Glossary Ethiopian living in sub-Saharan Africa (south of 30 degrees north) and Madagascar. Nearctic living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico. Neotropical living in the southern part of the New World. In other words, Central and South America. Palearctic living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa. acoustic uses sound to communicate agricultural living in landscapes dominated by human agriculture. benthic Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent. bilateral symmetry having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria. biodegradation helps break down and decompose dead plants and/or animals brackish water areas with salty water, usually in coastal marshes and estuaries. carnivore an animal that mainly eats meat chemical uses smells or other chemicals to communicate coastal the nearshore aquatic habitats near a coast, or shoreline. colonial used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms. cooperative breeder helpers provide assistance in raising young that are not their own cryptic having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect. detritivore an animal that mainly eats decomposed plants and/or animals diurnal active during the day, 2. lasting for one day. dominance hierarchies ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates ectothermic animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature estuarine an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity. external fertilization fertilization takes place outside the female's body female parental care parental care is carried out by females fertilization union of egg and spermatozoan filter-feeding a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales. food A substance that provides both nutrients and energy to a living thing. freshwater mainly lives in water that is not salty. herbivore An animal that eats mainly plants or parts of plants. introduced referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action. iteroparous offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes). keystone species a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter). male parental care parental care is carried out by males mimicry imitates a communication signal or appearance of another kind of organism molluscivore eats mollusks, members of Phylum Mollusca monogamous Having one mate at a time. motile having the capacity to move from one place to another. natatorial specialized for swimming native range the area in which the animal is naturally found, the region in which it is endemic. nocturnal active during the night nomadic generally wanders from place to place, usually within a well-defined range. omnivore an animal that mainly eats all kinds of things, including plants and animals oriental found in the oriental region of the world. In other words, India and southeast Asia. oviparous reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body. parasite an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death pelagic An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone). pet trade the business of buying and selling animals for people to keep in their homes as pets. pheromones chemicals released into air or water that are detected by and responded to by other animals of the same species piscivore an animal that mainly eats fish planktivore an animal that mainly eats plankton polyandrous Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous). polygynandrous the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females. polygynous having more than one female as a mate at one time reef structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate. saltwater or marine mainly lives in oceans, seas, or other bodies of salt water. scavenger an animal that mainly eats dead animals scent marks communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them seasonal breeding breeding is confined to a particular season sexual reproduction that includes combining the genetic contribution of two individuals, a male and a female sexual ornamentation one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs. social associates with others of its species; forms social groups. tactile uses touch to communicate territorial defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement tropical the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south. vibrations movements of a hard surface that are produced by animals as signals to others visual uses sight to communicate year-round breeding breeding takes place throughout the year