Taxonomy & naming
Austrofundulus myersi was described by the Colombian zoologist Jorge Dahl in 1958, with the type locality recorded as Sincelejo, a city in the Sucre Department of northern Colombia. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid combination as Austrofundulus myersi Dahl, 1958, placing the species in the family Rivulidae, subfamily Rivulinae. The American Killifish Association classifies the genus as Class 3 South American Annuals, reflecting the diapausing-egg annual life strategy shared by all members.
The genus Austrofundulus is a small Neotropical group currently comprising around seven species — including A. limnaeus, A. transilis, A. guajira, A. leohoignei, A. leoni, and A. rupununi — all restricted to northern Colombia, northern Venezuela, and the western Guiana region centred on the Lake Maracaibo basin and lower Orinoco drainage. Within this assemblage A. myersi occupies one of the most northwesterly and geographically restricted distributions.
The specific epithet myersi honours Dr George Sprague Myers (1905–1985), the American ichthyologist whose foundational contributions to Neotropical fish systematics continue to underpin much of the family-level classification used today.
Morphology
Austrofundulus myersi is a moderately sized annual killifish reaching a maximum of 3 in standard length (FishBase; It Rains Fishes). Published meristics from It Rains Fishes give mean dorsal fin ray count of 16.4, anal fin rays 18.0, the dorsal-to-anal origin ratio 4.5, and a longitudinal scale count of approximately 32.8 — a meristic profile consistent with other members of the genus.
The body form is the typical stocky, somewhat laterally compressed shape shared by robust annual killifishes suited to shallow, often turbid floodplain pools. Males of Austrofundulus species typically carry vivid iridescent colour patterning — blue, green, and orange — while females are more cryptically coloured in browns and tans, a pattern of strong sexual dichromatism consistent with the open-pool, polygynous mating system of the genus. Detailed colour descriptions specific to A. myersi in the literature are limited by the scarcity of specimens and field observations.
Habitat
Austrofundulus myersi is endemic to seasonal floodplain savannas in the lower Magdalena River system of northern Colombia, in the corridor between Cartagena and Barranquilla on the Caribbean coast. The species inhabits temporary pools and shallow seasonal wetlands that form during the wet season over the savanna floodplain and contract or disappear entirely during the dry season — the defining environment for all annual Rivulidae.
Daytime water temperatures in these exposed savanna pools can reach 95 °F, dropping to around 77 °F at night, giving an unusually warm temperature range compared with many killi habitats (It Rains Fishes). The pools are typically shallow, with soft substrates of clay, mud, leaf litter, and organic detritus into which the fish spawn. The extent of occurrence for the species has been estimated at approximately 4,62 mi² and the population is known from only two to five locations — an extremely limited footprint that makes the species highly vulnerable to any localised habitat event.
Feeding
In common with other small annual killifishes of open floodplain pools, Austrofundulus myersi is presumed to be an opportunistic carnivore, feeding on invertebrates, small crustaceans, insect larvae, and zooplankton available in the seasonal pool environment. It Rains Fishes describes the species as a heavy feeder in captivity, accepting live, frozen, and dry prepared foods with equal readiness.
The fast growth rates typical of annual killies demand a high-protein diet, and captive specimens condition quickly on Daphnia, Artemia, bloodworm, and similar fare. Ensuring dietary variety and sufficient feeding frequency supports the rapid maturation that characterises the annual life strategy.
Mating
Austrofundulus myersi is an annual killi that mates in the substrate — the pair dive together into the soft sediment and deposit eggs directly into the mud, clay, or peat of the pool floor. This substrate-spawning behaviour is the defining reproductive character of the South American annual-killi guild and is fundamentally different from the surface or plant-spawning of non-annual killies.
Males establish dominance and court females in the shallow pool, driving rival males away. When a female is receptive, the pair press together and plunge briefly into the substrate, fertilising and burying a small number of eggs with each dive. The process is repeated across multiple substrate-spawning bouts over weeks to months until the pool dries. Males are typically more brightly coloured and larger than females, and the intense sexual selection of the brief aquatic season produces the strong dichromatism seen across the genus. The American Killifish Association records a collection code of COL 2006-01 associated with this species, indicating locality-traced hobby strains are in circulation.
Breeding
The eggs of Austrofundulus myersi are buried in soft substrate and enter diapause — a state of arrested embryonic development — that allows them to survive the dry season entirely without water. Development time in storage ranges from approximately 30 days to 12 months depending on how the eggs are kept, with humidity, temperature, and the substrate medium all affecting the timing (It Rains Fishes). When seasonal rains refill the savanna pools, the rehydrated substrate triggers hatching and the fry emerge into a world that has replenished its food supply.
In captivity the standard approach is to spawn the fish on peat fibre, coir, or maërl (It Rains Fishes notes that straight peat can be too acidic for this species; coir is preferred). The spawning medium is removed periodically, lightly dried, and sealed in a bag for the diapause period. Re-wetting the medium after the appropriate storage window prompts hatching, typically beginning within 30 or more days. Fry are relatively large and well-developed at hatching by annual-killi standards and accept Artemia nauplii from the start. Growth to sexual maturity takes only four to six weeks — the compressed timeline of a fish whose entire lifespan may be shorter than a single rainy season. A tank of at least 15 US gal is recommended for a breeding group of one male and two or more females.
In the aquarium
Austrofundulus myersi is a rewarding but specialist subject. The species requires the annual-killi husbandry skill set: a spawning medium in the tank (peat fibre or coir on the bottom or in a separate container), periodic removal and drying of the medium, and the discipline to store eggs through the diapause period before re-wetting. For killifish hobbyists already familiar with this workflow the fish is straightforward; for newcomers the technique has a learning curve.
Tanks of 15 US gal or more are appropriate, and It Rains Fishes suggests a ratio of one male to at least two females to distribute male attention. The warm savanna-pool origin means this is not a cold-water species: maintaining temperatures in the 77–86 °F range is appropriate, matching the natural night-to-daytime cycle of the floodplain pools. Floating plants and surface cover reduce stress. The species is not widely available in trade given its rarity and conservation status, but the American Killifish Association documents active hobbyist engagement through JAKA journal coverage and the COL 2006-01 locality strain circulating in collections.
Given the IUCN Endangered listing and the extremely small wild range, hobbyist breeding of documented locality strains contributes directly to ex-situ preservation of genetic diversity. Responsible record-keeping of collection codes and parental lines is especially important for a species known from so few wild specimens.
Conservation
The IUCN Red List assesses Austrofundulus myersi as Endangered (EN) under criterion B1ab(iii), assessed in October 2014 and published in 2016 (assessment by Jimenez-Segura et al.). The extent of occurrence is approximately 4,62 mi², the species is known from only two to five locations, and fewer than sixteen museum specimens have been documented — among the smallest datasets behind any Rivulidae assessment. The qualifier 'ab(iii)' denotes continuing decline in the quality of its aquatic habitat.
The primary driver of decline is the conversion and degradation of floodplain savanna wetlands in the lower Magdalena catchment by extensive cattle ranching. Livestock impoundment, drainage of seasonal pools for pasture, and modification of the natural flood pulse that sustains these ephemeral habitats all directly remove or degrade the breeding habitat of a fish whose entire life cycle — including egg storage — depends on the seasonal pool existing as a functioning system. No formal conservation measures for the species were in place at the time of the last assessment, and the IUCN recommended further research on distribution, population size, and threats as the first necessary step toward effective management.
The narrow geographic range, the complete dependence on a single threatened habitat type, and the near-total absence of population monitoring data make Austrofundulus myersi one of the more vulnerable freshwater fishes in northern South America. Hobbyist ex-situ breeding of documented wild-caught strains represents the only current conservation safety net.