Abstract:The Grijalva River basin is one of the largest hydrological systems in Central America. Despite its importance, an inventory of its ichthyofauna remains incomplete. We provide a systematic checklist of fishes recorded in the Grijalva River basin based on surveys performed from 2002 to 2015. The systematic list includes 92 species, belonging to 13 orders, 25 families and 50 genera, of which 83 species are native and nine are exotics. This checklist includes three range expansions (Profundulus hildebrandi, Poecilia sphenops and Paraneetroplus hartwegi). Fifteen species are endemic to the basin. The most diverse families are Cichlidae and Poeciliidae with 25 and 23 species, respectively. Secondary freshwater fish diversity is high with 65.1%, the remaining species are primary freshwater (13.3%) and peripheral (21.7%) fishes.

REBIEN), durante un periodo comprendido de 2004 a 2009. El elenco sistemático consta de 153 especies, que se incluyen en 2 clases, 20 órdenes, 52 familias y 107 géneros. Se registran por primera vez 9 especies para los ambientes continentales del estado de Chiapas, 4 en hábitat estuarino-lagunar en México: Cathorops cf. fuerthii, Trichiurus nitens, Guavina micropus y Gobionellusliolepis, las 2 últimas con distribución ahora extendida para el Pacífico mexicano. Destaca la presencia del cíclido exótico Oreochromis niloticus. Las familias más representativas fueron Carangidae (14 especies), Sciaenidae (11), Gobiidae (10) y Ariidae (9). Por su origen ecogeográfico, 4 especies (2.6%) son dulceacuícolas primarias, 13 (8.5%) dulceacuícolas secundarias y 134 (88.9%) periféricas; del conjunto periférico,3 especies (2%) son catádromas, 11 (7.2%) residentes estuarinas, 56 (36.6%) marinas eurihalinas y 66 (43.1%) marinas estenohalinas. Desde el punto de vista biogeográfico, 91.2% de las especies se distribuyen en el Pacífico oriental, de las cuales el 47.7% se encuentran en la Provincia Californiana, 65.4% en la Provincia de Cortés, 80.4% en la Provincia Panámica y 41.2% en la Provincia Peruviana. La REBIEN contiene una riqueza íctica comparativamente mayor a la registrada en ambientes estuarino-lagunares de otras regiones costeras del Pacífico mexicano.Palabras clave: peces estuarinos,

ABSTRACT1. Profundulus hildebrandi, the San Crist ! o obal pupfish, is a small cyprinodontiform fish endemic to the closed basin of San Crist ! o obal de Las Casas, a fast-growing city in highland Chiapas, Mexico. This study constitutes the first population study of this endangered taxon.2. In order to judge its conservation status, its distribution and habitat were described, and its population size was estimated through a capture-recapture technique. To the extent possible, present conditions of its habitat were compared with historic information, mainly old city maps and photographs.3. Introduction of largemouth bass (Micropterus salmoides) coincided with local extirpation of P. hildebrandi. Other risk factors related to urban growth include pollution of streams, as well as habitat destruction, fragmentation, and modification; about 60% of the original pupfish habitat is heavily polluted by sewage.4. Although its population size is apparently large (probably more than 8000), its very restricted distribution, its shrinking habitat and the increasing risk factors provide justification to consider P. hildebrandi as an endangered fish, according to the Mexican Official Norm and the Red Book of the IUCN.

Summary The effect of the preserver on the length‐weight relationship and condition factor were estimated using 50 specimens of Tlaloc labialis; a small stream fish from the Grijalva River basin, México. They were measured at different stages of preservation: freshly collected, fixed in 10% formalin and preserved in 70% ethanol for over a 2 years period. All fish decreased in weight and condition factor, with very significant differences compared to the fresh material. The value of the coefficient (b) increased and stabilized from the second month of preservation in ethanol.

Mangrove forests of Mexico have been threatened by the effects of anthropogenic activities during the last decades, mostly related to aquaculture, agriculture, livestock and urban development. Genetic diversity and fine-scale genetic structure of two generations of the black mangrove Avicennia germinans (L.) Stearn were investigated in perturbed and preserved sites from three lagoon systems in Sinaloa, Mexico. Genetic diversity and overall genetic structure were similar between perturbed and preserved sites. However, lower levels of fine-scale spatial genetic structure were observed in two of the younger (sapling) generations. We attribute this to differences in local dynamics of each lagoon system, their status of conservation and levels of fragmentation. Also, low connectivity and the effects of disturbance could restrict the movement of pollinators and seed dispersal capabilities, resulting in low levels of genetic diversity and signs of inbreeding. Perturbed populations of A. germinans may play an important role in in situ conservation of this complex ecosystem.