Cynolebias myersi (Carvalho, 1971); Nematolebias myersi (Carvalho 1971)
The genus Simpsonichthys was coined by Antenor Leitão de Carvalho in 1959, as a tribute to his friend Charles J. Simpson from California, U.S.A. The name is a combination of Simpson’s surname and the Ancient Greek word ἰχθύς (ikhthus), meaning ‘fish’.
Similarly, the species myersi is named after Dr. George Sprague Myers, an American ichthyologist who lived from 1905 to 1985.
- Order: Cyprinodontiformes
- Family: Rivulidae
The species is found in several minor river basins within the eastern Brazilian coastal plains, specifically between the rio Jucuruçu in southern Bahia state and rio Doce in Espírito Santo state.
The type locality is a temporary pool located approximately 18 km from Conceição da Barra, Espírito Santo, Brazil, along the road to Itaúnas, at coordinates about 18°30’S 39°40’W.
The population inhabiting the rios Doce and Barra Seca may correspond to Simpsonichthys izecksohni (Da Cruz, 1983), which is of uncertain taxonomic status as noted in the literature.
The species occupies ephemeral, shallow depressions, pools, and swamps that are sustained by rainwater and may experience complete desiccation for several months each year, primarily from July to November.
Adult individuals do not survive during this period, while the eggs enter diapause and await the return of rain (refer to ‘Reproduction’).
Maximum Standard Length
Male individuals can attain a length of 35-40 mm, while females are comparatively smaller.
To ensure optimal living conditions, a minimum aquarium size of 45 x 30 cm or greater is recommended for even a single pair, unless they are temporarily isolated for breeding purposes.
For optimal environmental conditions, it is recommended to utilize a dark substrate, and a few clusters of floating vegetation would be appreciated by the fish and provide a refuge for subordinate individuals.
Other decorative elements can include a plastic tub with a layer of spawning medium (refer to ‘Reproduction’). In case of filtration, an air-driven sponge-type unit is sufficient.
Due to their tendency to jump, a securely fitting cover should be considered essential for Simpsonichtys species.
- Temperature: 20 – 27 °C
- pH: 5.5 – 7.0
- Hardness: 18 – 90 ppm
A suitable diet for this species should consist of small live or frozen foods such as Daphnia, Artemia, whiteworm, mosquito larvae, etc. as they are natural micropredators.
It is recommended to avoid feeding excessive amounts of high protein or fatty foods to adult individuals.
Behaviour and Compatibility
To mitigate aggression, it is recommended to keep this species in a species-specific arrangement with at least 2-3 females per male.
Male individuals of this species attain slightly larger sizes than females and develop filamentous extensions on their dorsal and anal fins as they mature. Conversely, females only possess relatively short filamentous rays on the posterior margin of their anal fins.
The male colour pattern consists of 10-15 dark crimson to dark brown vertical bars against a brownish yellow to greenish blue background.
Females display 9-12 broad dark brownish grey bars on a pale brown background, usually with 1-3 vertically elongated to roundish black blotches on the anterior portion of their flanks and 1-3 small grey to black spots on the posterior edge of their caudal peduncle.
During the dry season, when the natural habitats of this species become desiccated, adult fish perish, leaving behind fertilized eggs that have a thickened, drought-resistant outer layer and are encased within the substrate.
The eggs remain in a state of diapause until the return of rains, which typically takes 4-5 months. Upon the arrival of rains, the eggs start to hatch, and the fry grow rapidly, reaching sexual maturity in as little as 3-4 weeks under favorable conditions.
Most breeders deposit eggs into soft substrates, utilizing a shallow plastic container filled with coconut fiber or peat moss (although the latter is environmentally damaging). Eggs should be stored at a temperature of 70-77°F/21.1-25°C for 2-4 months before being wetted.
The typical lifespan of this species in an aquarium is 6-16 months.
This particular species has a taxonomic history that remains somewhat perplexing, and its conspecific status with S. izecksohni (Da Cruz, 1983) is currently unresolved.
While Costa (2007) has considered S. izecksohni to be a synonym of S. myersi, the majority of authors have not accepted this conclusion, and both species are generally regarded as valid.
S. myersi can be distinguished from other members of the genus, except S. izecksohni, by its unique combination of characteristics, including the presence of filamentous rays on the posterior margin of the anal fin in females, a lanceolate and asymmetrical caudal fin with an expanded ventral portion in males, and a color pattern comprising a bar on the posterior portion of the caudal peduncle, extending posteriorly over the dorsal and ventral margins of the caudal fin in males.
The genus Simpsonichthys has undergone a somewhat unstable taxonomic history, beginning with its first proposal by de Carvalho (1959) and later its synonymization with Cynolebias Steindachner by Parenti (1981).
Afterward, Cynolebias was divided into four genera, including Spectrolebias Costa & Nielsen, Nematolebias Costa, Austrolebias Costa, and Megalebias Costa, while Simpsonichthys was reestablished (Costa, 1996). All of these genera remain valid, with the exception of Megalebias, which is now considered a synonym of Austrolebias.
Costa (2006) further split the genus Simpsonichthys into five subgenera, which are Simpsonichthys, Spectrolebias, Xenurolebias, Ophthalmolebias, and Hypsolebias, based on their morphology and phylogenetic relationships.
S. myersi and S. izecksohni were the only two species included in Xenurolebias based on the unique characteristics of S. myersi.
Costa (2007) then provided an extensive taxonomic revision of Simpsonichthys, which included descriptions, distributions, identification keys, and a revised taxonomy for all five subgenera and fifty species.
Although subgenera are not commonly used in modern systematics, the results of the revision did not significantly affect higher taxonomy, and all species remained within Simpsonichthys, typically referred to as Simpsonichthys (subgenus) species, such as S. (Xenurolebias) myersi.
Finally, in a study of the historical biogeography of the Cynolebiasini, a hypothetical tribe within the Rivulidae family, Costa (2010) considered Spectrolebias, Xenurolebias, Ophthalmolebias, and Hypsolebias to represent separate and distinct genera.
However, since no additional criteria or characters were provided to support this decision, the split and upgrade of subgenera to the generic level is not considered valid by the majority of authors, given that the assemblages are distinguished only by minor morphological details, and molecular studies are still lacking.
Thus, while Simpsonichthys may eventually prove to be genuinely paraphyletic and require splitting, the absence of concrete evidence makes the continual changes in taxonomy unstable. As an example, Spectrolebias was previously established as a valid genus, then considered a subgenus of Simpsonichthys, and finally revalidated as a genus within just thirteen years.
In conclusion, we maintain all species within Simpsonichthys on this platform, pending future studies.
- Costa, W. J. E. M., 2007 – Zootaxa 1669: 1-134
Taxonomic revision of the seasonal South American killifish genus Simpsonichthys (Teleostei: Cyprinodontiformes: Aplocheiloidei: Rivulidae).
- Costa, W. J. E. M., 2010 – Journal of Biogeography 37: 1995–2004
Historical biogeography of cynolebiasine annual killifishes inferred from dispersal–vicariance analysis.
- Costa, W. J. E. M., 2006 – Neotropical Ichthyology 4(1): 1-26
Descriptive morphology and phylogenetic relationships among species of the Neotropical annual killifish genera Nematolebias and Simpsonichthys (Cyprinodontiformes: Aplocheiloidei: Rivulidae).
- Costa, W. J. E. M., 1996 – Journal of Comparative Biology 1(3/4): 129-140
Phylogenetic and biogeographic analysis of the Neotropical annual fish genus Simpsonichthys (Cyprinodontiformes: Rivulidae).
- de Carvalho, A. L., 1959 – Boletim do Museu Nacional do Rio de Janeiro, Zoologia, Nova Série No. 201: 1-10
Novo gênero e nova espécie de peixe anual de Brasília, com uma nota sôbre os peixes anuais da Baixada Fluminense, Brasil (Pisces – Cyprinodontidae – Fundulinae).
- Murphy W.J. and G. E. Collier, 1997 – Molecular Biology and Evolution 14(8): 790-799
A molecular phylogeny for aplocheiloid fishes (Atherinomorpha, Cyprinodontiformes): the role of vicariance and the origins of annualism.
- Parenti, L. R., 1981 – Bulletin of the American Museum of Natural History v. 168 (art. 4): 335-557
A phylogenetic and biogeographic analysis of cyprinodontiform fishes (Teleostei, Atherinomorpha).