Taxonomy & naming
Tlaloc portillorum was formally described by Matamoros and Schaefer in 2010, based on specimens collected from tributaries of the Río Calam in the upper Ulúa drainage, Department of Comayagua, Honduras. The original description appeared in the Journal of Fish Biology (volume 76, issue 6, pages 1498–1507). Eschmeyer's Catalog of Fishes is the authority for the valid name, and the authority is presented in parentheses because the species has been moved from its original generic placement. A 2024 range-extension study by Matamoros and colleagues documented 21 new collecting sites in the ríos Patuca and Choluteca, substantially expanding the known distribution.
The genus Tlaloc — pronounced roughly TLAH-lock — is named after the Aztec rain deity Tlāloc, a fitting eponym for a group of stream fishes dependent on highland rainfall and intact watersheds. The family Profundulidae, to which Tlaloc belongs, is a small Mesoamerican endemic lineage within the order Cyprinodontiformes; phylogenetic work places it as the sister group of the pupfishes and their allies. Tlaloc portillorum is the southernmost species in the genus, and its occurrence on both the Atlantic and Pacific slopes of Honduras is noteworthy from a biogeographic standpoint.
The species epithet portillorum honours D. and H. Portillo, who guided the senior author to the type locality in the Honduran highlands. The fish is non-seasonal — it does not undergo the annual lifecycle of egg diapause and adult die-off seen in many South American and African killifishes — and inhabits permanent or near-permanent highland streams rather than the ephemeral pools typical of annual species.
Morphology
Tlaloc portillorum is a small, slender killifish reaching a maximum recorded standard length of 3 in in males (FishBase). The species is distinguished from its congeners by a combination of meristic features: dorsal soft rays number 10–15 and anal soft rays 9–14. The eye diameter is relatively small, less than one quarter of head length, which differs from the proportionally larger eye seen in some related Profundulidae. Pectoral-fin ray counts are also lower than in most congeners.
Colour in life is not extensively documented in the available literature; the species is rarely encountered in the ornamental trade, and detailed colour descriptions from the original description focus primarily on meristic and morphometric data. The fish shares the laterally compressed, moderately elongate body plan typical of the genus, adapted for life in flowing highland streams over cobble and gravel substrates. Sexual dimorphism is likely present as in other Profundulidae, with males typically more vividly marked, but specific data for this species are sparse.
Habitat
The Uluan killifish is a highland stream specialist found in small tributaries between approximately 1,340 and 1,2152 ft elevation in the Honduran interior. The type locality in the Río Calam system is characterised by streams 10–16 ft wide and 8–15.5 in deep, with a cobble substrate, roughly 60% canopy cover from riparian vegetation, and emergent macrophytes in quieter sections. These are permanent, oxygen-rich, cool-water habitats — a very different environment from the warm lowland swamps or ephemeral seasonal pools occupied by many other killifish groups.
The fish has been recorded in association with Alfaro huberi, the introduced Nile tilapia (Oreochromis niloticus), and the catfish Rhamdia laticauda. The presence of Oreochromis niloticus in these drainages represents both an ecological impact and an indicator of human alteration to the watershed. The broader geographic range now documented from the Nacaome, Patuca, and Choluteca river systems suggests that T. portillorum tolerates some variation in substrate and flow conditions across the Honduran highlands, but it remains a stream-dependent species tied to intact riparian forest and reliable highland rainfall.
Feeding
No detailed dietary study of Tlaloc portillorum has been published in the available literature. Based on the ecology and body plan of the species and what is known of related Profundulidae, the diet is expected to be opportunistic and invertebrate-focused — small aquatic invertebrates, insect larvae, and other stream macroinvertebrates likely form the core of the wild diet in the cobble-bed highland streams the species inhabits. Emergent and terrestrial invertebrates falling onto the water surface may also be taken.
In aquarium conditions, Profundulidae generally accept a wide range of live, frozen, and dry foods. Small live or frozen bloodworm, daphnia, and artemia, as well as appropriately sized prepared foods, are likely to be accepted. Because the species inhabits cool, fast highland streams, water quality and oxygenation are probably more critical to husbandry success than dietary specifics.
Mating
Tlaloc portillorum is a non-annual killifish that reproduces by depositing adhesive eggs on fine-leaved plants, submerged roots, or similar vegetation rather than burying eggs in substrate peat. This plant-spawning mode is characteristic of Profundulidae and contrasts sharply with the annual, soil-spawning strategy of many South American and African killifishes that inhabit ephemeral pools. The species' permanent highland stream habitat and comparatively long adult lifespan reflect this non-annual life history.
In plant-spawning killifishes generally, a conditioned pair will engage in courtship displays alongside vegetation or a spawning mop, with the male driving and displaying to the female before the pair press together briefly to deposit one or a small number of eggs at a time. This egg-by-egg process is repeated over days or weeks, with eggs adhering individually to the spawning medium rather than being broadcast or buried en masse. Specific courtship descriptions for T. portillorum are not available in the published literature, but the general Profundulidae pattern is well established.
Breeding
Eggs of plant-spawning Profundulidae are adhesive and incubate in water at the ambient stream temperature; there is no diapause phase, and development proceeds continuously. Incubation duration depends on water temperature — in the cool highland streams where T. portillorum lives, incubation is likely to be somewhat longer than in warm lowland species. Fry are relatively large at hatching compared to annual killifish and begin feeding on small live foods soon after absorbing the yolk sac.
In the aquarium, spawning can be encouraged by providing fine-leaved plants (java moss, hornwort) or synthetic spawning mops, clean cool water, and a varied diet of small live or frozen invertebrates. Eggs should be removed to a separate hatching vessel to protect them from the adults. The species has no diapausing egg requirement and does not need wet-storage or peat conditioning — eggs hatch directly in water. Because the fish is rarely if ever available in the ornamental trade, breeding accounts from hobbyists are essentially absent, and the above reflects the general Profundulidae reproductive pattern rather than species-specific observation.
In the aquarium
Tlaloc portillorum is not a species that appears in the mainstream ornamental fish trade, and captive maintenance is essentially undocumented outside of specialist herpetological and killifish conservation circles. Its status as an Endangered Honduran endemic means any captive-held individuals are likely to be ex-situ conservation stock rather than commercially bred ornamental fish.
For hobbyists interested in the Profundulidae or in maintaining conservation-relevant killifish, the husbandry requirements can be inferred from habitat data: the species needs cool, well-oxygenated water reflecting its highland stream environment, moderate current, a cobble or gravel substrate, and ample plant cover or refugia. It should not be kept in the warm, still-water conditions suited to most tropical ornamentals. A species tank or a tank with similarly sized, peaceful stream fish would be appropriate. The species is non-aggressive in the manner of most small killifishes, though males may compete with one another for territory or females.
Conservation
The IUCN Red List assessed Tlaloc portillorum as Endangered (EN) under criterion B1ab(iii) in February 2020. The extent of occurrence is estimated at 1,79 mi², the species is known from only three locations in the IUCN sense, and there is continuing decline inferred in the quality of its freshwater habitat. No protected areas encompass its known range, and no active conservation measures were documented at the time of assessment.
The threats are those familiar to highland freshwater fish throughout Central America: agricultural encroachment on riparian corridors, deforestation and the associated increase in sediment load and flashy hydrology, and the introduction of non-native fishes. Specifically, the IUCN assessment flagged the presence of an invasive Asian fish tapeworm (Bothriocephalus acheilognathi) confirmed in the Nacaome River system, as well as established populations of Nile tilapia (Oreochromis niloticus) in drainages within the species' range — both representing direct biological threats to a small, sedentary stream fish.
The 2024 range extension documenting 21 new collecting sites across the Patuca and Choluteca river systems is a meaningful update that may eventually lead to a reassessment of the species' extent of occurrence, though it does not by itself reduce the pressure from habitat loss and invasive species. The southernmost Profundulidae species, and one of the most narrowly highland-restricted, T. portillorum is a conservation priority within Honduras and for the wider Mesoamerican freshwater biodiversity programme.