Ma. de Lourdes Lozano Vilano

The name killifish refers to the oviparous secondary freshwater fishes in the order Cyprinodontiformes. Killifishes are abundant in Mexico and are represented by four extant families, Rivulidae, Profundulidae, Fundulidae and Cyprinodontidae, comprising > 50 species in a wide variety of habitats. This paper reviews the current classification of the killifishes of Mexico, as well as aspects of their distribution, biology, ecology and current population conservation status.

This study represents a thorough analysis ofCodoma,a monotypic genus endemic to north‐western Mexico. A previous morphological analysis of the species concluded that there exists several morphological groups inCodoma ornata, suggesting diversity inCodomacould be underestimated. No studies have examined the genetic diversity inCodoma ornatato test this hypothesis and identify independent lineages. We present a phylogeographic analysis using one mitochondrial and two nuclear genes, and specimens from across nine major drainages in both the Chihuahuan Desert and the Sierra Madre Occidental of western Mexico. All genes and analyses recovered populations ofCodomain a well‐supported clade and sister toTampichthys, and this clade sister toCyprinella. Analyses of both mitochondrial and nuclear genes indicatedCodomais not monotypic and recover more diversity in the genus than currently recognized. The four (mitochondrial) and five (nuclear) genetically distinct lineages are consistent with those groups outlined in the prior morphological study of the genus. Composition and distribution of these major lineages is also consistent with prior biogeographic hypothesis for other fishes in the region, supporting an ancestral Rio Grande system extending south towards central Mexico. Fragmentation of this paleosystem was followed by allopatric speciation in the Chihuahuan Desert. These results suggest a scenario of long‐term isolation in four major regions (upper Conchos, lower Conchos, Nazas, upper Mezquital). Resolution of the diversity and biogeography of these lineages has many implications for various biological disciplines, especially for evolutionary and conservation studies.

Three new species of the genus Herichthys are described on the basis of chromatic, morphometric, and meristic characters. Herichthys pratinus sp. nov. from the Rio Salto in San Luis Potosi is characterized by a steep and shallow predorsal profile, a concavity before the eye, and adult males with a prominent forehead forming a nuchal hump, DXV–XVI, 10–11; and AV, 8–9. Herichthys pame sp. nov. from the Rio Tamasopo in San Luis Potosi is characterized by a gradual and acute predorsal contour, lack of concavity before the eye, and mouth angled slightly downward. Herichthys. molango sp. nov. from Laguna Azteca, Hidalgo is distinguished by small eyes and a slender (slightly broader than long), well-spaced, and indented lower pharyngeal plate with 2 rows of 8–9 medium-sized, lightly pigmented molars flanking the midline. We also provide redescriptions for three species of Herichthys, H. pantostictus, H. labridens, and H. steindachneri and a review of H. bartoni.

Variation in mtDNA (cytb sequences) and six microsatellite loci was used to assess the conservation genetics and taxonomy of a group of populations of Gambusia in tributaries of the Rio Grande in Texas (USA) and Coahuila (Mexico): G. clarkhubbsi in San Felipe Creek, Texas, and G. krumholzi. The latter has been considered endemic to the Río de Nava of the Río La Compuerta system, Coahuila, but we found it more widely distributed, both in the Río La Compuerta and outside that system, with a population in the Río San Diego, another Rio Grande in Coahuila. Our results, including reassessment of the morphological characters used to describe G. clarkhubbsi, suggest that G. clarkhubbsi is a junior synonym of G. krumholzi. The San Felipe Creek population (G. cf. clarkhubbsi) had only the common cytb haplotype of G. krumholzi, and none of the microsatellite loci was diagnostic of the two. However, the San Felipe Creek population is the most divergent of the known populations of G. krumholzi. Diversity attributable to among-population differences was six-fold greater when the San Felipe Creek population was included in the AMOVA than when it was excluded (38.5% versus 6.5%). A search for evidence of genetic introgression by G. speciosa as a factor in microsatellite divergence found only one F₁ hybrid and two first-generation backcross progeny. Based on the genetic structure and restricted distribution of G. krumholzi, the San Felipe Creek population and four populations in Mexico are recommended as management units for future monitoring. La variación en el ADNmt (secuencias cytb) y en seis loci microsatélites se utilizó para evaluar la genética de conservación y la taxonomía de un grupo de poblaciones de Gambusia en tributarios del Río Bravo en Texas (EEUU) y Coahuila (México): G. clarkhubbsi de San Felipe Creek, Texas, y G. krumholzi. Esta última ha sido considerada endémica del Río de Nava del sistema del Río La Compuerta, Coahuila, pero la encontramos más ampliamente distribuida, tanto en el río La Compuerta y fuera de ese sistema, con una población en el río San Diego, otro tributario del Río Bravo en Coahuila. Nuestros resultados, incluyendo la reevaluación de las características morfológicas utilizadas para describir G. clarkhubbsi, sugieren que G. clarkhubbsi es un sinónimo menor de G. krumholzi. La población de San Felipe Creek (Gambusia cf. clarkhubbsi) tuvo sólo el haplotipo cytb más frecuente de G. krumholzi, y ninguno de los loci microsatélites fue diagnóstico de los dos. Sin embargo, la población de San Felipe Creek es la más divergente de las poblaciones conocidas de G. krumholzi. La diversidad atribuible a las diferencias entre poblaciones fue seis veces mayor cuando la población de San Felipe Creek se incluyó en el AMOVA que cuando fue excluida (38.5% versus 6.5%). Una búsqueda de evidencia de introgresión genética por G. speciosa como factor de divergencia microsatélite encontró sólo un híbrido F₁ y dos progenies de la primera generación de retrocruzamiento. Debido a la estructura genética y la distribución restringida de G. krumholzi, se recomienda que la población de San Felipe Creek y cuatro poblaciones de México se mantengan como unidades de manejo para monitoreo futuro.

The genus Cycleptus is widely distributed in the Mississippi, Missouri, and Ohio rivers and in Gulf-slope drainages, including the Rio Grande. Recent genetic evidence suggests that Cycleptus in the Rio Grande is an undescribed species; however, there are few specimens from Mexico. These include two records from the Río Conchos, two from the Rio Grande and another from the Río Salado. In 1954, Cycleptus was reported in two localities in the Río Conchos: 1.6 km N Saucillo and 1 km above the confluence of the Rio Grande and the Río Conchos. After a purported absence of 51 years, it has been rediscovered in three localities in the state of Chihuahua: the mouth of the Río Conchos at Rio Grande, Cuchillo Parado, and Río Conchos at El Alamo. El género Cycleptus se encuentra ampliamente en los ríos Mississippi, Missouri y Ohio y en las cuencas que drenan hacia el Golfo, incluyendo el río Grande. Estudios genéticos recientes sugieren que los peces de Cycleptus en el río Grande son una especie no descrita, sin embargo hay muy pocos especímenes de México. Entre estos figuran dos para el río Conchos, dos para el río Grande y otro del río Salado. En 1954, Cycleptus fue reportado en dos localidades en el río Conchos: 1.6 km N Saucillo y otro de 1 km arriba de la confluencia del río Grande y río Conchos. Después de una supuesta ausencia de 51 años, este ha sido redescubierto en tres localidades en el estado de Chihuahua: la boca del río Conchos en el río Grande, Cuchillo Parado y río Conchos en El Álamo.