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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 mg/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.

This study provides an assessment of the carrying capacity of water bodies in the area of Zacapu, Michoacan for
extensive and semintensive aquaculture with carp (Cyprinus carpio) by means of experimental trials in 27 ponds. A 3 x 3
factorial analysis with three densities (DB = 0.5 orgs. • m-2, DM=1 orgs. • m-2 and DA= 2 orgs. • m-2) and three feeding regimes (R0 = without fertilization, RF = fertilization and R+ = farming by-products) included nine combined treatments between densities and feeding regimes with three replicates for each case. The combination of low density and natural food, analog to an extensive aquaculture in small water reservoirs, attained a maximum yield equivalent to 5,000 orgs. • ha-1.
Empirical trials accomplished at seven temporary basins (<10 ha) under conditions of different stocking densities from
1,500 to 6,000 orgs. • ha-1 lead to fairly similar yields to those obtained in the ponds. Thus, the general index used in Mexico
for extensive aquaculture of 1 org. • m-2 overloads the regional temporary ecosystems and only the possibility of supplying
additional food allows rearing of a double amount of organisms and improves the results of this productive activity.

The present research focused on the functional role of the phytoplankton of an economically important endorheic tropical lake from the perspective of algal growth bioassays. The algal growth potential of the lake water was compared for littoral and pelagic sites during the wet and dry seasons. Algal growth potentials at open waters reached minimum and maximum values following the seasonal alternation of dilution (by rain) and concentration (by evaporation) respectively. Conversely, at southern littoral stations high algal growth responses related to the availability of nutrients from point contamination sites. There was no such effect at nearby offshore sites or elsewhere in the lake which suggests filtration and competitive interactions for these nutrients between phytoplankton and littoral macrophytes. Nitrogen and phosphorus both acted consistently as limiting nutrients at open waters by colimitation. Nitrogen to phosphorus ratios seemed to approach equilibrium where limitation easily shifted to one element or the other temporally and spatially.

In this paper, a basic question is asked about a well-documented case study in Mexico: how well do we know Lake Patzcuaro? We address water balance as fundamental to the question. Past studies provide ambiguous explanations about the role of either underground infiltration and/or runoff, relative to the lake-level fluctuation. Thus, our suspicions over the database reliability led us to inspect historic records on water levels and climatic variables; check out the altitude of ground references, and analyze traces of runoff watercourses over the terrestrial basin by means of GIS. By making data re-arrangement and corrections, it became evident that the lake is subject to longterm cycles with ca. 40-year peaks, including short-term seasonal cycles within. Sensitivity to climatic conditions was determined, as well as the active influence of runoff as an important hydrologic component that contributes to cause serious damage to the land surface by erosion. Rearrangement of raw data highlights the occurrence of past misinterpretations founded on biased information.

Historical aerial photography over closed basins enables the observation of lake surfaces at variable water levels and climatic conditions. Thus, the assessment at the landscape level of subtle variations in inundated areas depends on a suitable framework for processing historical imagery, frequently available at different scales and resolutions.

This study provides an assessment of the carrying capacity of water bodies in the area of Zacapu, Michoacan for extensive and semintensive aquaculture with carp (Cyprinus carpió) by means of experimental trials in 27 ponds. A 3 × 3 factorial analysis with three densities (DB = 0.5 org. · m–2, DM=1 org. · m–2 and DA= 2 orgs. · m–2) and three feeding regimes (R0 = without fertilization, RF = fertilization and R+ = farming by–products) included nine combined treatments between densities and feeding regimes with three replicates for each case. The combination of low density and natural food, analog to an extensive aquaculture in small water reservoirs, attained a maximum yield equivalent to 5,000 orgs.· ha–1 . Empirical trials accomplished at seven temporary basins (&lt;10 ha) under conditions of different stocking densities from 1,500 to 6,000 orgs.· ha–1 lead to fairly similar yields to those obtained in the ponds. Thus, the general index used in Mexico for extensive aquaculture of 1 ...

This paper reports on the algal growth-limiting nutrients of five lakes located on Mexico’s Mesa Central - a topic poorly known in the regional limnology of Mexico. The five case studies involved three contiguous watersheds of Michoacán State and provided a trophic state variation from mesotrophic to hypereutrophic; the case studies included Lakes Zirahuén, Pátzcuaro, Teremendo, Cuitzeo and the Cointzio Reservoir. The fieldwork involved the collection of physical and chemical data (including nutrients) from each case study during the dry and rainy seasons of 2010. Additionally, water samples (1 L) were obtained and filtered (0.45 µm) in the laboratory to keep the nutrient content available for bioassays. The chemical analyses suggested a phosphorus (P) limitation in the Cointzio Reservoir, Lake Teremendo and Lake Zirahuén relative to an N:P&gt;16:1. There was a nitrogen (N) limitation at three sampling stations of Lake Pátzcuaro, with an N:P&lt;16:1. As result of the bioassays condu...

Homogeneity of water quality in a shallow endorheic lake in Mexico, Lake Patzcuaro, was studied through the analysis of 13 physical and chemical variables at 10 sampling stations monthly between January 1998 and January 1999. Principal components analysis associated most temporal and spatial variance with two variables: total residue and conductance. Spatial analysis discriminated between limnetic and littoral areas, and among shallow stations. Temporal analysis segregated four time intervals: cold/dry, warm/dry, rainy, and highest rainfall. Even though Lake Patzcuaro is a continuous warm polymictic lake, our results show its environmental heterogeneity; the lake is a physical and chemical mosaic.

El presente documento aborda el tema de la objetividad, un aspecto fundamental de la filosofia positivista aun imperante en las ciencias naturales que exige &quot;datos duros&quot; representativos de una realidad externa al ser humano, como una &quot;verdad&quot; a descubrir detras de la informacion. Un meta-analisis sobre las aportaciones en torno a la limnologia del lago de Patzcuaro, conlleva las siguientes preguntas: ?Como percibe el ser humano la realidad que le es ajena, en este caso la estructura y funcionamiento de un ecosistema acuatico? ?Los trabajos publicados en el caso de Patzcuaro acaso son ajenos a los intereses, deseos e inclinaciones del investigador? ?Cual es la aplicacion practica de la investigacion en torno a este caso de estudio? La revision de referencias sobre el tema comprenden las publicaciones existentes desde finales de la decada de los 1930s hasta la fecha.

El presente documento trata sobre las bases históricas, psicológicas y culturales que fundamentan la lucha social en las comunidades purépechas de Michoacán hacia una organización política de gobierno por “usos y costumbres”; es decir, un cuarto nivel de gobierno.

Resumen: El presente caso de estudio ecosistémico centrado en el lago de Pátzcuaro trata aspectos-ambientales, políticos, económicos y sociales-entrelazados-. La versión científica de la realidad desde el paradigma positivista sobrevalora los "datos duros" obtenidos en instalaciones frecuentemente apartadas del contexto histórico y social de las comunidades indígenas. La ganancia en "objetividad" desde una visión de "expertos" lleva implícito el costo de la inefectividad práctica para revertir el impacto humano sobre el ambiente lacustre.