Spatio-temporal variation of the ichthyofauna of a temporary river, in the Southern Mexican Pacific

Abstract

The Southern Pacific Coastal Plain of Mexico, particularly the Oaxaca-Chiapas region, is characterized by many permanent and temporary rivers and streams, most of which discharge into coastal lagoons and estuaries connected to the Pacific Ocean. The aim of this study was to analyze the taxonomic composition, abundance, and distribution of fish in relation to the environmental variables of a temporary river located on the Pacific coast of Chiapas. Four systematic samplings were conducted between September 2022 and January 2023, covering the rainy season (September–November), when the river maintained longitudinal connectivity, and the transition to the dry season (January), when surface flow persisted only at the uppermost site. A total of 1,901 specimens belonging to 7 species, 6 genera, 5 families, and 4 orders were collected. Significant differences in fish abundance were observed among sampling sites and months, highlighting the influence of environmental conditions. Poecilia sphenops and Poeciliopsis pleurospilus were the most abundant species at sites with higher temperatures and low dissolved oxygen (DO) concentrations, whereas Profundulus punctatus predominated at sites with lower temperatures, higher DO concentrations, and greater depth. Similarity analysis revealed the formation of two groups of sites along the river’s longitudinal gradient, reflecting differences in species composition and ecological affinity. The results indicate that the structure of the fish community in this temporary system is influenced by physicochemical gradients and hydrological connectivity, emphasizing the importance of remnant refuges for the conservation of fish diversity in the region.