Male in the aquarium
A male of Thorichthys pasionis in the aquarium of Juan Miguel Artigas Azas, note the distinctive black gill membranes. Photo by Juan Miguel Artigas Azas. determiner Juan Miguel Artigas Azas








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Thorichthys pasionis (Rivas, 1962)


Original description as Cichlasoma pasionis:


  • Rivas, Luis Rene. 1962. "Cichlasoma pasionis, a new species of cichlid fish of the Thorichthys group, from the Rio de la Pasion, Guatemala". Quarterly Journal of the Florida Academy of Science. 25(2):147-156 (crc00275)

Taxonomic history:

Etymology: pasionis refers to the type material collecting place, Rio de la Pasión, an affluent of the Usumacinta river system in Guatemala.

Common names: Mexico: Mojarra de la Pasion; United States: Blackgullet cichlid, Yellow meeki .

Types: holotype: UMIM 4872 (1), paratypes (7): UMIM 4017 (7).

Diagnosis: The higher number of gill rakers (18-20) and the coloration of the upper lateral line, with small, well-defined black spots, one on each scale distinguish Thorichthys pasionis from the other species in Thorichthys (Rivas, 1962:154).

Size: According to Miller (Miller, 2005:379) the maximum size of Thorichthys pasionis is 118 mm in standard length, some 15 cm in total length.

Sex dimorphism: Thorichthys pasionis does not show a noticeable sexual dimorphism, males grow larger and show larger threads in the unpaired fins. Females often have larger bellies.

Type locality: Río de la Pasión at Sayaxche, Río Usumacinta drainage, Deptartamento del Petén, Guatemala.

Distribution: Thorichthys pasionis is always found sympatrically with Thorichthys meeki, as it inhabits a great part of the range of the latter. The yellow meeki has its westernmost range in México in rivers and lagoons in the lower Grijalva river around the city of Villahermosa, north to the mouth of the Grijalva-Usumacinta river system. The yellow meeki range extends eastwards reaching the Rio Usumacinta affluents in the Petén area in northern Guatemala, where it seems to be especially abundant. Thorichthys pasionis range includes Rio Usumacinta affluents San Pedro and la Pasión. The species is also found in the basin of the rivers Chompán and Candelaria, all these rivers flowing to the gulf of México. Thorichthys pasionis is absent in the north and south-eastern parts of the Yucatán peninsula and in Belize, in the basin of the rivers Hondo, New River, Belize, and Sibun, where Thorichthys meeki extends his companion range.

Habitat: Thorichthys pasionis seems to be especially fond of lagoons and rivers with soft muddy bottoms and slow flow to stagnant water. They are inhabitants of the shallow parts of rivers and lagoons, where they are normally found in groups of all ages. The water in the yellow meeki inhabits is normally low visibility, although not murky. Temperature range between 24º to 30º Celsius, pH always on the alkaline side, from 7.5 up to 8.5. Hardness is variable with measurements of 8 degrees and up of General Hardness.


Conservation: Thorichthys pasionis is evaluated by the international union for the conservation of nature in the iucn red list of threatened species as (LC) least concern (2018). Not listed in the Mexican Official Norm NOM-059-ECOL-2001 with any degree of protection. Although faced with pollution in part of its range, most of it remains relatively stable.

Feeding: Thorichthys pasionis feeds in loose groups in shallow areas of the habitat. It wanders facing downwards and picking on the substrate, creating small pits in it, more than sifters Thorichthys are pickers, they do not systematically pick on every area of the substrate like sifter cichlid species (e.g. Crybroheros robertsoni) do, the way the locate their preys has not been studied to my knowledge. Material picked up is scrupulously examined in the mouth and inedible matter expelled through mouth and gills, while softer material is filtered by gill rakes. Thorichthys are carnivorous and I have never seen them collecting vegetable matter, although it may be ingested as a sub-product of the picking process. Thorichthys pasionis has a longer snout and a a larger number gill-rakers than of T. meeki, which may be an indication that T. pasionis picks in a deeper layer of substrate for food.

Breeding: Bi-parental, substrate spawning cichlids. Pairs are formed from February to May. Eggs yellowish, adhesive, and rather small in size with a maximum length of 1.7 mm (Coleman & Galvani, 1998), over five hundred per spawn in adult pairs. Pairs take extended care of the fry.

Aquaristics: Thorichthys pasionis is not very aggressive and is a very beautiful cichlid that can easily be kept in the home aquarium. To obtain their more brilliant colors, however, it is necessary to keep them in the best conditions. They do not require such large tanks as most Central American cichlids - 250 liters, at least 1.20 meters long will suffice. Most of the time a tank this size will be large enough for a group of them, but I would nevertheless advise a tank at least 1.50 m long. Always choose a larger surface area in preference to deeper tanks (area is more important than height). When aquascaping, it is best to simulate their natural surroundings as described above, fine sand substrate (avoid mud, though!) and plenty of cover being best. This fish does much better when kept in groups. It's always better for them to look a little (just a little!) crowded in order to divide their aggressiveness between multiple targets and at the same time produce more natural behavior. Dither fish are also an important part of the environment that should be provided. Thorichthys pasionis do well with large poeciliids (very small ones are eaten under aquarium conditions) as well as with many other similar, non-aggressive but fast-moving fish. In spite of their cichlid aggressiveness, given the right size aquarium yellow meeki ignore fish that do not pose direct competition. Yellow meeki will greedily eat most foods offered, but although they are carnivorous, try to avoid offering them warm-blooded animal meat, which can typically cause them digestive problems that can lead to death.

Comments: The evolutionary history of Thorichthys pasionis is a whole complete mystery. The species must certainly have some kind of ecological relationship with the syntopic Thorichthys meeki, the firemouth cichlid, but what is it? Hard to tell without any possibility of studying them in the cloudy water of the habitat. What is it that prevents them from hybridization (assuming they don't) in the wild? What provided the grounds for two species to evolve sympatrically? If they did. There is, of course, the possibility that they evolved geographically separated from each other and later came to overlap, but this doesn't appear to be indicated by the paleogeography of their distribution. I have kept an 800 liters aquarium with these two species for several years and found that under aquarium conditions they do hybridize, although on just a few occasions. So what are the forces preventing this in the wild?.

References (8):

  • Coleman, Ron & A.P. Galvani. 1998. "Egg size determines offspring size in neotropical cichlid fishes (Teleostei: Cichlidae)". Copeia. 1988:209-213 (crc01251)
  • IUCN. 2002. "IUCN Red List of Threatened Species". International Union for the Conservation of Nature (crc01159)
  • Instituto Nacional de Ecología (INE). 2001. "NORMA Oficial Mexicana NOM-059-ECOL-2001". Mexico (crc01158)
  • Kullander, Sven. 1996. "Heroina isonycterina, a new species of cichlid fish from Western Amazonia, with comments on cichlasomine systematics". Ichthyological Explorations of Freshwaters. 7(2):149-172 (crc01223) (abstract)
  • Lyons, Tim J. 2019. "Thorichthys pasionis". The IUCN Red List of Threatened Species. e.T192915A2179855. DOI: 10.2305/IUCN.UK.2019-2.RLTS.T192915A2179855.en (crc11752) (abstract)
  • Miller, Robert Rush. 2005. "Freshwater Fishes of Mexico". University of Chicago Press, Chicago. 1-524 (crc01245)
  • Miller, Robert Rush. 1966. "Geographical distribution of Central American freshwater fishes". Copeia. 1966(4):773-802 (crc01105) (abstract)
  • Rivas, Luis Rene. 1962. "Cichlasoma pasionis, a new species of cichlid fish of the Thorichthys group, from the Rio de la Pasion, Guatemala". Quarterly Journal of the Florida Academy of Science. 25(2):147-156 (crc00275)


Artigas Azas, Juan Miguel. (Dec 11, 2005). "Thorichthys pasionis (Rivas, 1962)". Cichlid Room Companion. Retrieved on Mar 02, 2024, from: (crc10823)