To start the exploration of the wonderful world of cichlids I thought it would probably be in order to take a deeper view on what a cichlid really is. Probably some readers of this article are thinking that they know all about it. They may, but even so explaining it is not an easy job. After all, how can you tell people that a species such as the amazingly shaped Amazon basin discus fish Symphysodon aequifasciatus and a species of the rheophilous (current loving) elongated Teleocichla, for example T. cinderella from the Tocantins River in the Amazon basin, are both cichlids? And then explain them that Laetacara curviceps from the Lower and Middle Amazon basin and the externally similar blue perch Badis badis from Asia belong to different families (Cichlidae and Badidae) and just very distantly related?
In preparing this article I re-read my two favorite explanations of what a cichlid is: that of George Barlow in “The Cichlid Fishes: Natural Great Experiment in Evolution” (2002:21) and that of Paul Loiselle in “The Cichlid Aquarium” (1987:6). The explanations found in those books are deep and beautiful and if you want to get deeper into it I would highly recommend reading them.
Most aquarium keepers are familiar with cichlids because of the extremely popular and extraordinarily beautiful freshwater angelfish, although to the true, the angelfish (or the discus fish) is an extreme of an evolutionary adaptation not like any other of the 1,700+ valid cichlid species.
Angelfish have evolved that particular shape of a flat disk with very elongated dorsal and anal fins and long threads, a silver color base adorned with black vertical bars to be able to blend in the environment and escape potential predators. I was able to fully appreciate that by standing on a canoe in the Macuari Lake, a lake located off the Branco River in Amazon basin in Brazil. While standing still on the boat, I could see an entanglement of branches in clear water. With patience and paying close attention I started spotting angelfish, first one, and then a second, a third! Once my eyes were accustomed and searching for the pattern I was able to see that there were in fact a large group of them just below me. I was completely fascinated.
For giving a quick idea to a person not familiarized with aquarium keeping I tend to set an example and ask them if they have seen a Tilapia. People may be familiar with this widely available freshwater food fish, which normally refers to a species in the African genera Sarotherodon or Oreochromis. Once they recognize a Tilapia I tell them that is an example of what a typical cichlid looks like, warning them that cichlids may however exhibit a wide variation in shape, color and size, going from less than five centimeters in length in a species like Taeniacara candidi to almost a meter for some species like Cichla temensis, both found in the Amazon basin.
But then, after this example is given some people tend to confuse the sunfishes of the family Centrarchidae for cichlids (same case as when many aquarists may confuse Badis badis for one) and this is where I explain that many unrelated organisms are externally similar because they have evolved to adapt to similar ecological conditions, an effect known as evolutionary convergence. Nonetheless, I tell them that there are unique characteristics that clearly demark cichlids, so there is no confusion at all.
In the general binomial organization of living beings initially proposed by Carl von Linné (Carolus Linnaeus as he Latinized his own name) in 1758, cichlids belong to the family Cichlidae. A family is one of the eight major taxonomic ranks in which living beings are organized, in the third step of the ladder between species to domain. As for other classification ranks, all organisms belonging to one taxonomic family group share some uniquely distinctive traits that form the diagnosis for that family and relate them together.
The family Cichlidae was proposed in 1835:11 by Prince Charles Lucien Jules Laurent Bonaparte (1803 - 1857), a French biologist and ornithologist that happened to be the nephew of Emperor Napoleon Bonaparte. He proposed a classification for all fish in his work “Prodromus systematis ichthyologiae” dated on 1835.
For his new family (which he proposed as the subfamily Cychlini in the family Chromididae) Bonaparte selected as representative (type) the genus Cichla Bloch & Schneider 1801. The type species of Cichla is C. ocellaris, so the representative of the family Cichlidae is this species, I believe a wonderful selection. Up to 1835, 51 species (Five by Carolus Linnaeus himself) of fishes that eventually ended in the family Cichlidae had already been described.
If case you are wondering which the first species of cichlid to be described was, there were five species (although one is a synonym) described in the original Systema Naturae by Caroulus Linnaeus in 1758 that ended up in Cichlidae. The species are currently known as Crenicichla saxatilis (p. 278), Sarotherodon galilaeus (p. 282), Cichlasoma bimaculatum (p. 285 - described also as Labrus punctatus in the same page) and Oreochromis niloticus (p. 286).
In the major classification scheme of life forms cichlids are classified in the phylum Chordata (just as we humans are), this phylum includes the vertebrates and earlier forms. Then cichlids are classified in the class Actinopterygii, which refers to the ray-finned fishes. Under this level they are classified in the Order Perciformes (also known as Percomorpha), the most numerous order of vertebrates with over 200 genera and about 12,000 species (Barlow, 2002, 2002:13) , these are the perch-like fishes. This order is however not yet clearly delimited and some of the families included may be reclassified in the future. Currently defined characteristics include species with pectoral fins on the sides of the body; spines on the dorsal and anal fins; pelvic fins on the abdomen with one spine and up to five soft rays; dorsal and anal fins that are detached from the caudal fin; and a jaw that can be projected forward to suck food into the mouth.
The family Cichlidae has been clearly defined by a diagnosis that includes nine unique anatomical characteristics (Kullander, 2003). However, those characteristics are not externally visible. Nevertheless, cichlids can also be recognized by a combination of three external characteristics, that is, although some non-cichlid may have one or the other, just cichlids have the three of them. They are:
- A fused dorsal fin that is formed by a frontal part with hard spines and a rear part with soft rays, other fishes have two dorsal fins instead (Think on the European perch as an example).
- One nostril on each side of the head, most fish possess two closely placed nostrils on each side of the head that are actually a U-shaped tube with two exits that allow water to circulate through it. Cichlids have each nostril ending in a bag with no exit; this specific adaptation is apparently not yet fully understood.
- A lateral line that is split in two parts. The lateral line is a tube which longitudinally crosses the flanks of the fish just under the skin. Each scale has a pore that connects the tube to the exterior and can be clearly seen on the flanks. The frontal part of the lateral line is somewhat downward curved running from the operculum in the upper part of the flanks to somewhere before the end of the dorsal fin. The second part runs straight by the middle of the flanks from the place where the first line ends to the middle part of the caudal peduncle.
The purpose of the lateral line is to detect water pressure by means of tiny receptor hair cells found all along it that feel it and communicate it to the brain. Each of the pores on the scales allow for water to come in. A problem with this trait is that two cichlid genera of Africa: Gobiocichla and Teleogramma, have adapted to live in the very fast flowing water of areas of the Congo River by means of developing a very elongated tubular body. Probably because of this adaptation, that leaves no space for two lateral lines, they have reverted to possess just one (2002, 2002:22).
For many people, who include evolutionary biologists (who study evolution), ethologist (who study animal behavior) and most importantly for us aquarists, cichlids are much more than possessors of a given set of taxonomic characteristics. Cichlids are fishes that exhibit a fascinating and elaborated behavior and a breeding ritual with an elaborated courtship, nest or spawning site construction and subsequent protection of their fry by the pair or at least by the female, until they reach independence. In other fish families that provide fry care, the male is the only one participating.
Cichlids also give their keepers the display of beautiful colors and different feeding specializations, and yet come with a challenge for those who want to keep them that serve to increase their appreciation: that of aggressiveness. Restraining and balancing that aggressiveness is a challenge most aquarists find fascinating, and sometimes frustrating, but yet keep the flame of interest high.
Aggressiveness may range from the very mild and harmless like in the angelfish: Pterophyllum scalare, to the extreme when the species is impossible to keep in a group in a home aquarium, like with the wolf cichlid Parachromis dovii from Central America, a potentially over 60 cm long predator with big teeth and a nasty disposition.
Most importantly for aquarists, many cichlid species are easy to keep and lead to reproduce under captive conditions, giving their keepers the pleasure to sit in the first row of one of nature’s beautiful spectacles. Most cichlids can thrive in most except the most extreme water chemistry conditions, giving every aquarist the choice of many species to work with.
Environmentally cichlids are referred as secondary freshwater fish, a term applied to fishes that having evolved from marine fish, are tolerant (as oppose to primary freshwater fish) to brackish and even in some cases pure sea water. One particular Central American cichlid species has often been spotted breeding in the sea, I am referring to the Mayan cichlid, Mayaheros urophthalmus. I have personally seen them breeding in sea water under the euroclima (frontier between salt and fresh water in some coastal springs and cenotes) at Cenote Manatí just north of Tulum in Quintana Roo, among mangrove roots. In a separate example, the wide coastal distribution of some species of cichlids like the black-belt cichlid Vieja maculicauda in Central America, which is found from Costa Rica to Belize in the Caribbean slope, is attributed to their tolerance to salt water, which allowed it to migrate between river mouths.
Cichlids inhabit in practically any water body that can supply them with a source of food. The can inhabit for example in salt and coastal lakes. They can also inhabit just certain areas of lakes that offer them protection and a source of food, either in open water or limited to a substrate like mud, sand, rocks, vegetated areas, shell-beds (which are areas covered by empty snail shells) or other areas that provide a specialized source of food. Riverine cichlids include those that are found in the main channels of rivers, those that are found in floodplains and marshes, those that have adapted to live in the very fast flowing areas and those that are just found in small creeks.
Cichlids have exploited all potentially possible shapes and feeding specializations. We have cichlids that feed on detritus (which is organic decaying matter), generalized and specialized herbivorous. Those specialized herbivorous can be algae combers, cutters, pickers, pullers, scrappers. There are also cichlids that feed on fruits that fall on the water from surrounding trees.
The carnivorous cichlids are equally generalized or specialized predators, there are crustacean eaters, insectivorous, molluscivorous, omnivorous, piscivorous; some of them hunt for their prey in the open water and some of them sift through or dive in the substrate to find them. And even some jump out of the water to get to them!
There are even bizarre specializations like those cichlids that feed on scales of other fish and those that feed on the babies of cichlids kept inside their mouth by their parents, so called paedophagous. Yet there are generalized omnivorous cichlids.
As you can see, the diversity of cichlids is mind blowing and the possibilities to study them and enjoy them are endless, as we will see in the fore-coming essays in this column.
- Barlow, George W.. 2002. "The Cichlid Fishes (Nature's Grand Experiment in Evolution)". Perseus Publishing. pp. 352 pp. (crc03927) (摘要)
- Bonaparte, Charles Lucien. 1835. "Prodromus systematis ichthyologiae". Nuovi Annali delle Scienze naturali Bologna. v. 2(n. 4), pp. 181–196, 272–277 (crc06466)
- Kullander, Sven. 2003. "Family Cichlidae (Cichlids)". Check list of the freshwater fishes of South and Central America. pp. 605-654 (crc01092)
- Linnaeus, Carolus. 1758. "Systema Naturae, Ed. X.". Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. 10 i-ii + pp. 1-824 (crc00310)
- Loiselle, Paul V. 1987. "The Cichlid Aquarium". Tetra Press. 1-447 (crc05987)
© Copyright 2018 Juan Miguel Artigas Azas, all rights reserved
Artigas Azas, Juan Miguel. (十月 10, 2018). "What is a cichlid?". Cichlid Room Companion. 检索 七月 22, 2019, 从: https://www.cichlidae.com/section.php?id=296&lang=cn.