Cichlid Room Companion


On the balsas living diamond; "Cichlasoma" istlanum Jordan and Snyder 1899

By , 1991. printer
Juan Miguel Artigas Azas,

Classification: Species overview, Central and North America.


'Cichlasoma' istlanum male in Papagayo River, Mezcala, Balsas. Photo by Juan Miguel Artigas Azas.

Ruling the underwater environment of the Mexican largest Pacific drainage, the Balsas river system, lives as the solely native representative of the cichlid family a beautiful fish of magnificent colors and interesting habits, 'Cichlasoma' istlanum.


'Cichlasoma' istlanum owns it's name to the American ichthyologists Jordan & Snyder, who scientifically described this fish in 1899 from specimens collected at the town of Puente de Ixtla ( 18°37'12", W.lon. 99°19'20") in the headwaters of Rio Amacuzac, a northern Rio Balsas affluent running southwards in the Mexican Morelos state. The original description was published in the Bulletin of the United States Fish Comm. together with a drawing of the fish, where the type locality gave Istlanum its specific name.

Istlanum, First placed in the cichlid genus Heros by it's describers, was later moved by the ichthyologist C. Tate Regan (1905) to the genus Cichlosoma and placed in his new subgenus Parapetenia. Subgenus that after a year was relegated to a section of Cichlasoma by the same Regan (1906). In this genus the fish remained until the big Cichlasoma mess started in 1983 once the Swedish ichthyologist Sven Kullander (1983) restricted the genus to some South American representatives closely related to the type species, Cichlasoma bimaculatum (Kullander, 1983). At that point the generic status of istlanum as well as that of around a hundred of other Central American cichlid species placed in that genus was left in the air.

It has been suggested then that Istlanum according to it's feeding technics could be considered part of the genus Nandopsis Gill 1862 (Konings, 1989), but recently Dr. Robert Rush Miller from the University of Michigan (Pers. comm., 1993), who is working with Central American cichlids, told me that Nandopsis will probably be restricted to the cichlid fishes of the Greater Antilles including the oldest known fossil representative of Central American cichlids, Nandopsis woodringi from Hispaniola island.

So, it seems 'Cichlasoma' Istlanum will have to wait for a genus of his own when more study is carried on about the former Middle American representatives of the genus Cichlasoma.


The Rio Balsas runs westwards in the southwestern part of México, having its origins at high altitudes in the Mexican states of Oaxaca, Morelos, Michoacán and Jalisco, where snow melted from the high volcanoes and water collected from rains by lands in the upper Mexican plateau feed the springs that give birth to this geographically sinuous river.

Most of the extensive path of the Balsas is found among the mountains of the Southern Mother Ridge of México, and this winding route has even give place to a boat racing marathon of international importance. Running west from Ciudad Altamirano the Balsas river serves as border between the States of Guerrero and Michoacán, continuing to it's mouth in the Pacific coast at the city of Lazaro Cárdenas ( 17 56'28", W.lon. 102 07'57").

The course of the Balsas mostly consist of rivers of moderate fast to very fast water flows, running on terrains that are rocky but also muddy in bottom composition. This is why the that waters of the lower balsas rivers cannot be expected to be very clear, so that only in the headwaters of smaller affluents is there visibility in the dry season. However, in my experience clarity is no more than five meters in exceptional cases. Wheteher this prevailed in the past I wouldn't know, since it is a fact that land deforestation has contributed its deal to this situation. During the rainy season Balsas rivers have a strong reddish brown color with no more visibility than perhaps 1 mm, indicating the high contents of fine clay being washed away.

The range of 'Cichlasoma' istlanum is not restricted to the Balsas river system, but it also extends to smaller systems west to Sierra Coloma at 20 in the Jalisco state south of the city of Puerto Vallarta, including Coahuayana and Armeria river systems. This mountain range acts as a barrier for istlanum distribution, the other side of which makes the beginning of that of the istlanum sibling species 'Cichlasoma' beani Jordan 1888. Although I have read reports and seen photographs of 'Cichlasoma' istlanum collected in Sierra de Manantlán (Lyons 1991) in Jalisco and Rio Comala; Armeria (Turner, 1989) in Colima, it seems the cichlid must be scarce west from the Balsas. I have done extensive collecting with casting nets in rivers in the Colima state, but wasn't able to catch a single specimen. It is true that the cichlid is hard to collect but I also found out talking with the people that live in the river course that mojarras cannot be encountered. Snorkeling in the few rivers where this was possible also was unproductive. Pollution plays its role, and rivers, especially the lower Armeria and Coahuayana systems, are stroked hard by human thoughtlessness. Rio Coahuayana being almost destroyed by the untreated wastes of a huge paper factory north of the city of Colima.

It is important to state that, as for other Central American cichlids, Istlanum is just found in parts of the rivers with a maximum altitude of 1000 meters above sea level and then just in those waters that are not too cool for them. I would say, according to my experience, not colder than 20°C to 22°C, like those rivers fed by cold-water springs. This fact limits the istlanum habitat to a fraction of it's potential range, as Balsas tributaries courses are found in a good part above this altitudes. Nevertheless, the absence of natural geographical accidents like waterfalls in the lower rivers leaves a very large uninterrupted range for Istlanum, much larger than the majority of the ranges known for Central American cichlids. We have to add that 'Cichlasoma' istlanum is the only natural cichlid in the Balsas, and so it has no competition for habitat.

The extensive range of 'Cichlasoma' istlanum has given origin to several geographic color forms of the fish, the one shown in the photographs I have to admit being not the most colorful variant but coming from one of the few areas I know where the water is clear enough to take underwater photographs, Rio Papagallo in the Guerrero State ( 17°08'07", W.lon. 99°35'40").

'Cichlasoma' istlanum coming form northern tributaries in the state of Morelos including Tequesquitengo ( 18°36'23", W.lon. 99°45'17"), an artificial lake where the fish apparently was introduced, show a more colorful variant, with stronger and more denser coloration. Cichlids coming from the western part of the range are distinguished from eastern counterparts by the stronger green coloration, mainly in the head area.


Rio Papagayo
Rio Papayago, Mezcala, Balsas at the cross with the old Highway México-Acapulco. Photo by Juan Miguel Artigas Azas.

The chemistry of the Balsas water is from neutral to alkaline and hardness readings are from hard to very hard. Measurements I took in Rio Amacuzac at the town of Tehuixtla yielded temperature readings of 27°C, PH 6.9, GH 65 , KH 11, confirmed closely in two occasions with a time span of several years. At Rio Papagallo, a southern affluent of the Balsas, measurements I took were very much alike with a temperature of 29°C, PH 7.6, GH 43, KH 15 .

Plant life is found in some rivers in the form of large weeds that the fish use for cover (Rio Amacuzac), but mostly no aquatic plants are found in the main courses of the rivers where istlanum lives. Big boulders are however very usual in the fish range, and those are efficiently used by Istlanum for cover purposes, something that makes them hard to collect with the use of nets. Sandy bottoms are usual in the rivers among the boulders, and muddy areas are to be found everywhere in back water or shallower zones.

Fish companions are found in several fish families, the larger being the catfish in the genera Ictalurus, represented by Ictalurus balsanus in the Balsas river and Ictalurus dugesi in the Rio Armeria. Livebearers are better represented, species of Allodontichthys, Ilyodon, Poecilia, Poeciliopsis and Xenotoca are common in the fish range (mostly in Rivers Coahuayana and Armeria) and Xenotaenia resolanae is located in Rio Ayuquila;Armeria, in Sierra de Manantlán. A minnow, Algansea aphanea, is also found in rivers Coahuayana and Armeria and the redhorse sucker Moxostoma austrinum in Rio Armeria. Goby genus Awaous, Sicydium, Dormitator, Eleotris and Gobiomorus are also present. The mullet so called "Fire land trout", Agonostomus monticola, and the tetra Axtyanax fasciatus, are also found in the whole range.

There are also many introduced species, African cichlid representatives like Tilapia rendalli and Oreochromis aureus are found in the whole range, introduced by the Mexican government as a dietary supplement for people in the region. North America is represented by Lepomis macrochirus, the bluegill, found in the Tequesquitengo lake and Herichthys cyanoguttatus in the same place and now in upper Amacuzac (Mistakenly described as a new species "Parapetenia cyanostigma" by Antonio Hernández Rolón in 1989). Also central America is represented in upper Rio Amacuzac by the recent introduction by hobbyists of Archocentrus nigrofasciatus that has bloomed, becoming a possible threat to 'Cichlasoma' istlanum populations.


'Cichlasoma' istlanum
A 'Cichlasoma' istlanum pair changing turns in the care of the spawn, Papagayo River, Mezcala, Balsas. Photo by Juan Miguel Artigas Azas.

'Cichlasoma' istlanum

'Cichlasoma' istlanum female caring for her spawn on top of the dug out cave under the boulder. Photo by Juan Miguel Artigas Azas.

'Cichlasoma' istlanum

'Cichlasoma' istlanum female caring for the wrigglers placed on the pit dug on the base of a pebble. Photo by Juan Miguel Artigas Azas.

'Cichlasoma' istlanum

'Cichlasoma' istlanum female caring for the wrigglers placed on the pit dug on the base of a pebble. Photo by Juan Miguel Artigas Azas.

'Cichlasoma' istlanum is not a very large cichlid, the largest male I have ever seen in the wild being no more than about 20 centimeters in total length, and this includes males with large frontal gibbosities, though aquarium specimens are known to have reached 25 centimeters (Adcock, 1991). The overall shape of the fish is elongated with a compressed body, a slightly curved profile with a concavity above the eye and a slightly exposed almost straight pre-maxillar pedicel. Large males develop gibbosities in the frontal area when breeding. Other features are thick lips and a lower jaw a little bit longer than the upper one. Dorsal and anal fins with filaments that extend beyond the middle of the rounded caudal fin, in some cases the dorsal filament beyond the end of it.

In normal coloration the fish shows several black blotches along the middle part of the flanks, those more conspicuous being the first, located at the base of the head, one in the middle of the body (which is the only one seen in juveniles), and one at the base of the caudal fin, those first and last ocelated with small scales containing blue spots in the middle. Basic color base is yellowish, lighter in the lower half of the body and much darker to brown in the upper one, the lower part also with a lot of red. Every scale on the flanks show a blue spot larger than those in the ventral area. The head of the fish is dark green in the dorsal area and yellow with an intense green hue in the ventral one. Fins are translucent showing blue iridescent spots and small red lines that become dots in the first third of the caudal fin.

In breeding individuals the red of the lower half of the flanks becomes very intense as well as the dark in the upper part, becoming in males velvety black up to about five black blotches that form a line in the upper part of the flanks and are just clearly visible in dominant individuals. Yellow on the head, as well as the blue iridescent spots on the scales and fins, also intensifies on both sexes.

My observations on 'Cichlasoma' istlanum show that they are usually a shy gregarious fish moving close to the river floor in small groups among the banks, stopping once in a while to shovel their mouths several times in the sandy or muddy bottoms to get a mouthful of substrate that they filter in search for any edible matter, proceeding afterwards to spit the rest back to the substrate. In this situation they look like a peaceful fish.

Breeding activity takes place during the dry season in the slower flowing parts of the rivers near the shores, normally on muddy substrates where the pairs already formed look for a rock where they dig a small cave that fit them at the base of it. The female then deposits well above five hundred small, almost invisible yellowish eggs on the ceiling of the rock, not thoughtfully cleaned for this purpose; the male then proceeds to fertilize them.

Spawns are cared for by the pair, males in the vicinity of the spawning place and females staying close to the eggs and mouthing them most of the time. Females are substituted by the males every once in a while, short time that the female uses to disappear from the spawning area in search of food. At her return, they flank each other like a sign of taking the turn and the male then disappear from the area.

The eggs hatch (after two days under aquarium conditions) and small wrigglers are placed in the bottom of the cave where they remain until they become free swimming (after five days in aquarium). At this time the female stays closely above the cave just peaking her head to take a close look at her babies every couple of minutes, preventing with her mouth that any dirt may cover them; after that she returns to her position, the male at this time surrounds apparently careless the nest in circles about a meter in radio.

I have observed that other cichlids at the sight of the guarding male just change subtly their route to avoid the nest vicinity, any careless fish that comes too close is then chased away by the angry male.

Wrigglers become free swimming and at this point they abandon the nest for good, both parents staying close to guide them through the shallow and quiet waters of the river to graze for food, mainly the male showing the route with the typical 'Cichlasoma' spasmodic movements of his fins and the female staying close to the heart of the fry cloud. Fry can be watched grazing on any surface, but with predilection for rocks where they seem to find attached algae and small invertebrates.

Luck and parents care will tell at this point the future of the little fish. I have observed lucky parents with herds of more than one thousand 2 cm fry, strolling proudly with their babies in the shallows of the river. I have also observed many pairs of cichlids with small fry just the day before an unexpected storm out of season falls; when the storm has passed not a single pair with fry was observed in the river.

Juveniles can be encountered gregariously in the shallows mainly close to overhanging vegetation, where they seem to stay until they become strong enough to swim in the currents and join a group of larger conspecifics.

there are no obvious predators of 'Cichlasoma' istlanum, since there are no fishes large enough in the Balsas to prey on them, but it seems that the high ability of the fish to hide under rocks and avoid casting nets even in the shallows could be an indication of strong pressure by fish eating birds that are present in good numbers in the cichlid range.


The bigger danger this beautiful cichlid faces is as usual of human origin; introduction of exotic species, both for food or amusing purposes plus the careless pouring of wastes in the river courses, are some acts that pose a risk to all freshwater fish populations in the world. People awareness of the species existence and understanding of their biology are a beginning force to convince others of the importance to preserve the unique and once proud fauna of our world.

'Cichlasoma' istlanum male

'Cichlasoma' istlanum male guarding his fry in the shallow areas of the faast flowing Rio Papagayo, Balsas; México. Photo by Juan Miguel Artigas Azas.


  • Adcock, Kent, 1991, "Cichlasoma istlanum: a diamond in the rough", Vol. 8 No. 4:9-14.
  • Danko, Don, 1988, "Collecting in México part I", Buntbarshe bulletin, No. 125: 2-7.
  • Gerritsen, John, 1988, "New sightings of unusual Cichlids in England", Cichlasoma Power, Vol. 6 No. 3:12-14.
  • Konings, Ad, 1989, "Cichlids from Central America", T.F.H. publications, pag. 33,39,40,46,189,197.
  • Kullander, 1983. "A revision of the South American Cichlid Genus Cichlasoma (Teleostei: Cichlidae), Stockholm.
  • Lyons, John, 1991, "Fishes from the land of the trucha de tierra caliente". Freshwater and Marine Aquarium Magazine: Vol 14/7;127-136.
  • Regan, C. Tate, 1905. "A revision of the fishes of the American cichild Genus Cichlasoma and of the Allied Genera". Ann. Mag. Nat. Hist. Ser 7(16): 324-327.
  • Regan, C. Tate, 1906-1908. "Pisces. In: Biologia Centrali Americana.
  • Turner Bruce J, 1989. "The Ilyodon Story", Tropical Fish Hobbyist, Vol 37-38/11,12-1;112-122.


Artigas Azas, Juan Miguel. (May 27, 1996). "On the balsas living diamond; "Cichlasoma" istlanum Jordan and Snyder 1899". Cichlid Room Companion. Retrieved on December 04, 2021, from:

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