Bioaccumulation of microcystins by fish associated with a persistent cyanobacterial bloom in Lago de Patzcuaro (Michoacan, Mexico)

Abstract

Lago de Patzcuaro is a historically important freshwater fishery in Mexico. The lake is presently characterized by a persistent bloom of cyanobacteria, specifically dominated by recognized producers of toxic microcystins (MCYSTs). We evaluated MCYSTs in sestonic and dissolved fractions of the water column, as well as representative fish species (silversides, Chirostoma spp.; Goodea sp.; and carp, Cyprinus carpio) obtained from local markets and small commercial catches during the bloom. Samples were evaluated primarily by enzyme-linked immunosorbent assay (ELISA), and secondarily by protein phosphatase (PPase) inhibition assay and liquid chromatography-mass spectrometry (LC-MS). Sestonic MCYST concentration (0.02-0.36 µg/L) generally correlated inversely with distance from the bloom, supporting the bloom as the source of the toxin. Several MCYST variants, including MC-LR, -LA and -LY, as well as didemethyl variants, were identified by LC-MS/MS analysis. All three species of fish bioaccumulated MCYSTs in relevant tissues, and toxin content correlated with trophic level, with highest and lowest levels measured in phytoplanktivorous and zooplanktivorous representatives, respectively. Detection of MCYST in silversides and Goodea sp. is particularly relevant because both are consumed in their entirety, including viscera (e.g., liver) known to primarily accumulate MCYST. These results indicate that Lago de Patzcuaro is indeed characterized by a toxigenic bloom, and that commercially important fish species from the lake accumulate toxic MCYST in tissues relevant to human consumption. As such, this system may represent an ideal model of the trophic transfer of MCYSTs and its relevance to human and environmental health.

Long term changes in the fish fauna of Lago de Patzcuaro in Central Mexico

“…Water depth has decreased >5 m, water volume has lost >150 Mm 3 and water transparency has decreased >3 m over the same period Orbe-Mendoza et al, 2002). Fisheries were one of the most important economic activities during the earlier (1900s to 1960s) decades (Berry et al, 2011) (Berlanga-Robles et al, 2002;Huacuz, 2002;Orbe-Mendoza et al, 2002).…”

“…It has a maximum depth of 12 m at maximum capacity and an average depth of 5 m. Water volume is determined by precipitation, evapotranspiration, and inflows from springs at the bottom of the lake and flows from small creeks in the watershed . The lake has experienced a 6 m water level decline since 1939 (Berry et al, 2011). Lago de Pátzcuaro is circadiomictic and is generally considered eutrophic ( Berry et al, 2011).…”

“…The lake has experienced a 6 m water level decline since 1939 (Berry et al, 2011). Lago de Pátzcuaro is circadiomictic and is generally considered eutrophic ( Berry et al, 2011). There are 26 urban areas surrounding the lake including one densely populated island (Isla Janitzio) in the southern part of the lake.…”

“…Lago de Pátzcuaro is located in the highlands of central México and has been subjected to several hydrological modifications: erosion and runoff from deforested uplands, loss of surface area, reduction of the water column (approximately 6 m and 166 Mm 3 in the past 70 years), lower water transparency (approximately 2 m in the past 40 years), hyper-eutrophication, and point source contamination from local communities throughout the lake (Alvarado-Díaz et al, 1985;Chacón-Torres, 1993;Berry et al, 2011). Lago de Pátzcuaro supports one of the best-studied, for the last three decades, inland fisheries in México; many of its endemic species have been intensively fished since long before the colonial times (De Buen, 1941;Orbe-Mendoza & Acevedo-García, 1995;OrbeMendoza et al, 2002).…”

“…Lago de Pátzcuaro supports one of the best-studied, for the last three decades, inland fisheries in México; many of its endemic species have been intensively fished since long before the colonial times (De Buen, 1941;Orbe-Mendoza & Acevedo-García, 1995;OrbeMendoza et al, 2002). However, fishery production from this lake has shown major fluctuations over the last 20 years and it is currently in sharp decline (Berry et al, 2011). Many of its fish populations are on the verge of collapse (Orbe-Mendoza et al, 2002).…”