Erick U. Vazquez Cano, Texas A&M International University

Investigating the Cause of Dead Fish Washed Ashore on an Artificial Lake in South Texas

Abstract: Hundreds of dead fish washed ashore were reported during the month of January 2018 on an artificial lake in South Texas. Locally referred as Bartlett Pond, the 4.5-acre waterbody is part of a soccer complex located near the Laredo International Airport. The purpose of this study was to determine a cause for the drastic decimation of the fish. Hypothesizing that water conditions were not suitable for aquatic life, water and soil samples and several fish carcasses were collected and subjected to analysis. Parameters of pH, temperature, electric conductivity, total dissolved solids (EC/TDS), and dissolved oxygen were taken in situ, but these measurements were found to be normal. High levels of phosphate and abundant algae in the area confirmed the phenomenon of eutrophication. However, normal levels of dissolved oxygen indicated that oxygen depletion was not responsible for the mass decimation of the fish. Spectroscopic data revealed the putative presence of microcystins, hepatotoxins produced by certain types of freshwater cyanobacteria. In parallel, results of heavy metal analysis indicated the presence of arsenic in extremely high concentrations in sediments and fish tissue. It is thought that the combination of these deleterious factors led to the mass decimation of fish. The eutrophic lake, with abundant algae, might have promoted the accumulation of microcystins. The fish, which were particularly debilitated by the extremely high levels of arsenic, became particularly susceptible to the hepatotoxicity of the microcystins, resulting in death. Current research focuses on confirming the presence of microcystins and their concentration in the fish.

Presentation Author(s):
Erick U. Vazquez*, David I. Marquez, Virginia M. Morales, and Estefania Padilla

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