Taxonomy & naming
Tlaloc candalarius was described by the American ichthyologists Carl L. Hubbs and Edward C. Raney in 1946. The Catalog of Fishes (Eschmeyer, CAS) records it as a valid species within the genus Tlaloc, family Profundulidae — the family that groups the endemic Mesoamerican killifishes, separate from the larger North American Fundulidae and from the South American aplocheiloids. The parentheses enclosing the authority name indicate that the species was not originally placed in the genus Tlaloc as it is circumscribed today.
The genus Tlaloc is named after the pre-Columbian Aztec deity of rain, water, and fertility — an evocative choice for a group of fishes whose distribution is tied to the mountain watersheds and highland streams of what was once the heartland of Mesoamerican civilisation. The specific epithet candalarius is a Latinised place-name or patronym referenced in the original description; the exact etymological intent is not recoverable from the sources available, but the naming pattern is consistent with many of Hubbs's geographic or dedicatory epithets.
Within the Profundulidae, Tlaloc is the smaller of the two recognised genera (the other being Profundulus). Relationships within the family, and the family's placement among Cyprinodontiformes, have been refined through molecular phylogenetic work published since the original description. The species is not known to have accepted synonyms in current use.
Morphology
Detailed morphometric data for Tlaloc candalarius are sparse in publicly available sources, and the following reflects what can be established from the Profundulidae literature and the Catalog of Fishes entry. Like other members of the genus, T. candalarius is a small killifish with the general body plan typical of the family: laterally compressed to subcylindrical, with the upturned mouth position characteristic of surface-oriented feeders, and a rounded to slightly pointed snout.
Size data are not firmly established in accessible sources, but Profundulidae members are generally small fishes in the range of 1–2.5 in total length at maturity, and T. candalarius is expected to fall within this range; more precise measurements would require access to the original description or museum specimens. Coloration details from the original description and subsequent revisionary literature are not reproduced in the cache sources available for this article. Users with access to the 1946 Hubbs and Raney paper or to ichthyological museum material will find the diagnostic morphological data there.
Habitat
Tlaloc candalarius is native to highland stream habitats in south-central Mexico, in the watersheds of the Sierra Madre del Sur and adjacent upland drainages. Members of the genus Tlaloc are associated with cool, clear, well-oxygenated streams and spring-fed waters at elevations substantially higher than those inhabited by most lowland killifish — conditions that set the Profundulidae apart ecologically from their relatives in the warmer lowlands.
Specific water-chemistry records for T. candalarius are not available in the sources underlying this article. By analogy with other Profundulidae from similar highland environments, the species likely tolerates or prefers cooler temperatures, moderate to neutral pH, and moderate hardness consistent with the calcareous geology of highland Mexican drainages, but these parameters should not be taken as verified for this species specifically without access to field-collected data.
The broader genus occupies clear, often fast-flowing to moderate-current streams with rocky or gravelly substrates, submerged vegetation, and overhanging riparian cover. Land-use change, deforestation in Mexican highland catchments, and extraction for agriculture and municipal supply are the principal pressures on this habitat type.
Feeding
No detailed dietary studies for Tlaloc candalarius appear in the accessible literature. The upturned mouth position common to the Profundulidae is consistent with surface and near-surface feeding on small invertebrates — aquatic insect larvae, terrestrial insects that fall to the water surface, zooplankton, and similar items. This feeding guild is typical of small-bodied killifish in lentic and slow-lotic habitats across Mesoamerica.
In an aquarium setting, comparable Profundulidae are usually willing to accept small live and frozen invertebrates (Artemia nauplii, Daphnia, chironomid larvae), and most will condition to small dried foods over time. Because the natural diet of this species has not been documented in accessible published sources, these observations are extrapolated from congeners and should be treated as provisional.
Mating
Tlaloc candalarius is a non-annual killifish: it inhabits permanent or near-permanent highland streams rather than seasonal pools subject to annual desiccation, and consequently reproduces as a plant or substrate spawner rather than burying diapausing eggs in sediment. In non-annual killifish of this type, pairs typically engage in courtship displays in which the male pursues and courts the female, culminating in a spawning clasp during which adhesive eggs are deposited individually or in small numbers on fine-leaved plants, submerged roots, algal mats, or other structures near the substrate or water surface.
Spawning in non-annual Mesoamerican killifish is not a single mass event but a protracted, intermittent process: a pair may deposit a few eggs each day over an extended period, with eggs incubating in water at ambient temperature without a diapause phase. Details of the mating display and any territorial or nuptial coloration for T. candalarius are not recorded in accessible sources.
Breeding
As a non-annual plant-spawner, Tlaloc candalarius produces adhesive eggs that adhere to vegetation or other surfaces and develop continuously in water — there is no obligate dry period or diapause, distinguishing this species sharply from the annual soil-burying killifish of seasonal tropical pools. Incubation period and fry size are not documented in publicly available literature for this species specifically.
In comparable non-annual Mesoamerican killifish, eggs typically hatch within one to three weeks depending on temperature, producing small but relatively advanced fry that can take Artemia nauplii or micro-worms from early on. The adults do not guard the eggs and may consume them if not separated. Maintaining a cooler water temperature consistent with the highland origin of the species is likely important for successful breeding in captivity, though confirmed thermal data for T. candalarius are not available in the sources reviewed here.
In the aquarium
Tlaloc candalarius is not an established aquarium fish. The genus Tlaloc and the family Profundulidae are essentially absent from mainstream hobby distribution; the species is largely unknown outside specialist killifish societies and ichthyological collections. No care sheets or dedicated husbandry accounts appear in the hobby sources reviewed for this article.
For aquarists who do obtain specimens — likely through specialist exchanges or field-collected material — the highland origin of the species suggests that cooler temperatures (perhaps 61–72 °F, based on altitudinal analogy with other Profundulidae) and well-oxygenated, moderately hard, neutral to slightly alkaline water would be appropriate starting conditions. A densely planted, covered aquarium with a gentle current would replicate the stream-margin microhabitat. Because of its rarity and the lack of a self-sustaining captive population, responsible husbandry should prioritise breeding and strain preservation. Any aquarist keeping this species is encouraged to connect with the American Killifish Association or equivalent regional body to share observations and support captive propagation efforts.
Conservation
Tlaloc candalarius has not been formally assessed by the IUCN Red List; no assessment record is available. This absence of evaluation is itself a conservation concern: the species' range is restricted to highland drainages in south-central Mexico, a landscape under sustained pressure from deforestation, agricultural expansion, water extraction for irrigation and municipal supply, and rural population growth. Small, range-restricted freshwater fishes in fragmented upland catchments are disproportionately vulnerable to localised extinction.
The Profundulidae as a family contain several species with restricted ranges and limited available data, and conservation attention to the group has historically lagged behind that given to more commercially prominent freshwater fishes. Tlaloc candalarius specifically requires field survey work to establish the current extent of its range, population trends, and the severity of threats — data that would support a formal IUCN assessment. The ongoing degradation of Mexican highland watersheds through land clearance and water-course modification makes such assessment and monitoring work urgent. In the absence of a formal status, the species should be treated as potentially at risk by any collector or holding institution.