Amphilophus istlanus was first described by Jordan and Snyder in 1899. The species is named after its type location Rio Ixtla, south of Cuernavaca in the province of Morelos Mexico.
Synonyms: Cichlasoma istlanum, Heros istlanus, Herichthys istlanus, Heros mento, Cichlasoma leonhardschultzei, Cichlasoma leonhard-schultzei, Cichlasoma istlana fusca.
Admittedly .., Amphilophus istlanus .., named “Living diamond” by Juan Artigas in 1991 and a few years later in 1996, promoted by the same author to “King of the Balsas”, is unquestionably the most beautiful native of the Balsas basin. All the more unfortunate that we hardly ever get to see this fish. This species is considered problematic within the hobby. The old aquarium strains are often affected by intestinal problems. Recently, during a catching trip by Heiner Garbe (a well-known aquarist from Germany), wild-caught was again imported. The experiences with these new imports from the Rio del Oro (a tributary of the Balsas) are promising. This variant seems more vital than the older aquarium strains. Hopefully, this will ensure the continuation of this species within our hobby for the time being.
In the wild, the istlanus do not grow larger than about 20 centimeters (Juan Artigas 1991) but in the aquarium literature dimensions of up to 30 centimeters are reported. Color and drawing are variable. In breeding dress, the basic color is yellowish, belly with red-rimmed, blue iridescent scales, which create an attractive checkered pattern. A beautiful red-blue stripes pattern can also be seen in the dorsal- and anal fins. Back with black crossbands, which sometimes merge and then darken the entire top of the fish, often a sign of dominance.
According to Meek (1904), there would be a variant in the Yautepec with an inverted color pattern. Dark from below and light from above. De Buen (1946) even thought he had to distinguish a subspecies Cichlasoma istlanum fuscum in the Rio Marqués (the green variant) and in 1935 Ernst Ahl described a younger synonym Parapetenia leonhard-schultzei. All observations suggest a wide variety of local forms, entirely in accordance with the relatively large distribution area.
The Rio Balsas basin in the South of Mexico flows into the Pacific. From the Rio Armeria in the province of Jalisco to the Rio Papagallo in the province of Guerrero. Amphilophus istlanus inhabits flowing rivers with a stony bottom and is the only indigenous Cichlid. In large parts of its distribution area, however, it is displaced by exotic species such as Amatitlania nigrofasciata.
In addition to its largest contiguous distribution area, the Balsas Basin, it is also represented in a few smaller river systems in the vicinity of this basin, all culminating in the Pacific, such as the Rio Coahuayana and Rio Armeria. In the West, a volcanic ridge beyond Colima separates its habitat from its related Mayaheros beani, and in the East, its distribution extends beyond Acapulco to the Rio Papagayo (Miller 2005) where Amphilophus trimaculatus takes over.
Amphylophus istlanus is important for local fishing. In recent years, however, the catch, both in numbers and in size, has drastically decreased. The species is strongly influenced by anthropogenic activities. Pollution, damming, and deforestation are taking an increasing toll. Also, the fact that the species turns out to be poorly resistant to competition and predation from exotic species such as sail fin catfish and convicts does not make the outlook any better. Artigas 1991 was no longer able to discover any Amphilophus istlanus in Colima, the most western part of the original habitat, and Heiner Garbe searched the species in vain for the type location, the Rio Ixtla. It is therefore in line with expectations that some variants will become rare in the future and, if not, will die out.
The experiences of enthusiasts vary somewhat. There are reports that istlanus was dominated by Cryptoheros species, but there are also reports where Istlanum decimated peers one by one. Possibly age made the difference here. The fact remains that the animals can strike against each other unexpectedly. Enthusiasts report regular losses on the internet without detecting any significant aggression beforehand.
It seems that Amphilophus istlanus avoids aggression in its pre-sexual period. In the wild, the fish still lives in schools and aggression would only turn out to be negative. Later, when the animals mature sexually, that outcome tilts. Aggression plays an important role in competition and the protection of territory and offspring. The early adolescents don’t spend time bluffing. Later, when the animals get a little older, Amphilophus istlanus uses bluff. Why would you risk your life if blowing your forehead yields the same result….
The foraging behavior is similar to that of many other Central American Cichlids. In the wild Amphilophus istlanus swims, soil-oriented, in small groups between the sandbanks. Stopping every now and then, bite into the sand a few times, and then filter out edible parts (Artigas 1991). Their food consists of a large part of soil-living insects, larvae, and snails. They can, deliberately or not, also eat detritus and algae. This group-wise foraging behavior naturally disappears when the animals start to breed.
In the aquarium, we can feed the Amphilophus istlanus in varied ways, but we must place one comment. Although in nature they undoubtedly eat larvae from Diptera, it has been found that mosquito larvae, at least in the old aquarium strains, can lead to intestinal problems. There is therefore a broadly based advice not to feed them mosquito larvae.
Breeding Amphilophus istlanus
Amphilophus istlanus is an open substrate breeder. Females stay smaller, often more contrast-rich, with the color red dominating the lower half. Males grow tall, and often have a forehead hump (especially in the vicinity of other males) and the color blue dominates the lower half of the body.
Amphilophus istlanus probably breeds only once a year in nature (Axelrod 1993). This then happens in the dry season. They then go into the slow-flowing parts of the river in search of an overhanging stone that offers them some extra protection. At the foot of that stone, they dig away the loose sand, after which the female lays about 500 almost invisible eggs at the bottom of the stone. Then they are fertilized by the male. This then remains in the vicinity of the nest, while the female takes care of the eggs directly. Sometimes she is relieved by the male, while strikingly flanks while passing. After two to 4 days (depending on the temp) the eggs hatch. The larvae are spat out one by one into the pit at the foot of the stone. After another 5 days, the fry are free swimming. Then they leave the nest for good. Both parents now stay close to the young. Using fin movements, they lead them to low-flow, nutrient-rich algae fields where the young feast on young arthropods and single-celled organisms.
The weather in this region can be decisive for successful or unsuccessful reproduction. Juan Artigas observed many couples with fry the day before an unexpected storm. A day later, he no longer found a couple with fry. This also makes it immediately clear why Amphilophus istlanus does not breed in the rainy season. As soon as the fry become independent, they school together and like to stay in the shade of overhanging vegetation in the shallower bank zones (Artigas 1991).
For an adult couple of Amphilophus istlanus, an aquarium size of 180 centimeters must be considered as a minimum (see behavior). Extensive shelter must be provided. A small group of them can be kept from aquarium lengths of around 250 centimeters. Keeping together with other large cichlids is possible but unnatural. Amphilophus istlanus is the only cichlid in the Balsas Basin. Only the most Eastern independent populations may experience (natural) competition from another Cichlid, namely the Amphilophus trimaculatus. The North-West border of Amphilophus trimaculatus somewhat overlaps the South-West border of Amphilophus istlanus, which does not mean that the species actually encounter each other. Amphilophus trimaculatus preferably inhabits the lower reaches (where the water tends to be brackish), while the sites of Amphilophus istlanus are more concerned with the upper middle reaches. Incidentally, there are reports of hybridization between these two species in the aquarium literature. Holding together is therefore not advised.
In the Balsas area, the livebearing Poecilia butleri is found in large numbers. This is the Pacific equivalent of Poecilia mexicana. I have not been able to find enthusiasts who combine Amphilophus istlanus with this kind of robust livebearing but it seems worth trying. Plants (apart from some weed fields) do not, or hardly, occur in the natural biotope of Amphilophus istlanus. A natural decoration for Amphilophus istlanus can therefore easily consist of sand stones and gravel.
Amphilophus istlanus is known as susceptible to intestinal infections. Young animals, particularly a few months old can die massively from this, but older animals also remain susceptible to intestinal problems. It is possible that stress plays a role in this. Overcrowding should therefore be avoided. The feeding of red mosquito larvae and tubifex is also widely discouraged because the latter often come from polluted waters. Some enthusiasts even abandon (for the reasons mentioned above) completely any form of live food.
This fish is generally kept too cold by aquarium enthusiasts. The optimum temperature for adult animals is 30 degrees Celsius and that of young animals is even 2 degrees higher. It is possible that this is also a cause of the bowel problems mentioned. Linked to this optimum temperature are also the enzymes that digest the food. These values have emerged from a study into the possibilities of commercially growing this species for consumption. Figueroa J.L. ed al. 2003. “Preferred temperature of the Mexican native cichlid Cichlasoma istlanum”. Hidrobiologica 2003, 13 (4): 271-275.
Rene Beerlink – NVC
Michael Negrini – Pisciculture d’Estalens
Jordan David Starr, J. O. Snyder. 1899. “Notes on a collection of fishes from the rivers of Mexico, with description of twenty new species” v. 19, pp. 115-147
Dr. Rüdiger Riehl en Hans A. Baensch. Aquarien Atlas 3, blz 734-735.
Bijgewerkt op 26 August 2023 door John