La Mintzita is a wetland located in the Southwest of the city Morelia, Michoacán. It is recognized as a Protected Natural Area and RAMSAR site due to its importance for the conservation of native flora and fauna. La Mintzita is the second most important wetland area in the state of Michoacán because it supplies the state capital, Morelia, with a third of the water consumed by its citizens. La Mintzita has reports for 13 fish species, nine of them native and four exotic.


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Fish diversity
Practice objectives

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Biological diversity is composed of all life forms existing on Earth, including ecosystems, animals, plants, fungi, microorganisms, and genetic diversity. According to the Convention on Biological Diversity, signed in 1992 at the Earth Summit in Rio de Janeiro, biodiversity is ‘the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species, and of ecosystems’. Thus, biodiversity includes all the ecological and evolutionary processes occurring at gene, species, ecosystem and landscape level.

It has been estimated that there are approximately 8.7 million species of plants and animals, of which only 1.2 million have been identified and described. This means that millions of organisms and biodiversity are yet to be discovered. 

Some countries such as Brazil, Colombia, Indonesia, China, and Mexico are considered the most biodiverse on the planet. The areas with extremely high levels of biodiversity are called ‘hotspots’. In these areas it is common to find endemic species, which have a restricted distribution to a reduced geographic region, and are not found in any other place on earth.   


Freshwater ecosystems, such as springs and wetlands, represent an important biodiversity reservoir and fulfil key ecological functions to provide society with ecosystem services. Fish are the vertebrate group with, by far, the most estimated number of species; from these around half are freshwater species. Mexico holds in its territory 6% of the world’s firewater fish species, or 60% of North American’s; that would be 506 species belonging to 47 families. The majority of these species are concentrated in Central Mexico.


Despite being among the most important biodiversity reservoirs, freshwater ecosystems are also between the most altered and invaded in the world. From all the North American fish extinctions of the 20th century two thirds are associated with introduced species. Freshwater ecosystems are vulnerable due to their geographic isolation and high rates of endemism. As it happens in islands, species inhabiting freshwater bodies are unable to exploit resources outside of them.


The establishment and population growth of invasive species alters native communities and ecosystem functions. Invaders are responsible for structural and compositional changes in ecological communities, through predation, competition, disease transmission, habitat degradation, and others. These changes lead to a disruption in the productivity and nutrient availability cycles within the habitat, which influence trophic structure and population dynamics. In some cases, invaders cause a radical alteration in the species composition of the place they had invaded which may ultimately lead to native species loss and wildlife homogenisation. Indeed, invasive species are the main cause of bird species going extinct and the second main cause of the extinctions of fish and mammals.


Due to the constant biodiversity loss associated to anthropogenic activities, it is necessary to employ tools that are able to measure how biodiversity changes in space and time. 


Methods to measure biodiversity

Ideally, to evaluate biodiversity at a global or regional scale, it would be necessary to measure the abundance of all organisms in space and time, using taxonomy (e.g., the number of species present), functional traits (certain species characteristics that allows them to perform different functions such as nitrogen fixation), and the interactions among species that can affect their function (e.g., predation, parasitism, competition).


The easiest way to measure biodiversity is to count species number or richness in a given area. There are 1) methods based on the quantification of the number of species present, and 2) methods based on community structure. Among the former, it is possible to calculate species richness (S, which is based only on the number of species present, without taking into account their importance value), or indices such as Margalef’s (which is based on the relationship between S and the total number of individuals observed). Among the latter are found the indices of proportional abundance, for example indices of dominance such as Simpson’s and indices of equity such as Shannon-Wiener’s. 


It must be taken into account that it is also important to quantify sampling effort, which can be measured as the number of collected individuals, or number of samples, traps, days, or any other measure of area or time. This is necessary to estimate the minimum effort that has to be invested sampling, according to the species accumulation curves. 


Rank-abundance curves are obtained by hierarchically ranking all the species present in the sample unit. Species abundance is represented on the Y axis, generally in a logarithmic scale. Species rank is represented on the X axis. The species of highest abundance is represented first, and following this order, an abundance profile by rank is obtained. These curves allow to identify how many species are the most abundant, how many species are rare, and what are the difference in abundance among all the sampled species. 

La Mintzita, Michoacán

La Mintzita is a spring and wetland in the outskirts of the city of Morelia, in Central Mexico, that provides the city with 33% of the water needed to supply its population. La Mintzita is also home of four species belonging to the Goodeidae family, which is endemic of Central Mexico, including the biggest goodeid species (Allophoros robustus). The Goodeidae family is composed of ca. 45 species, of which 15 are listed as endangered and at least two are considered extinct in the wild. Thus, this spring and wetland is of importance for both society’s supply of ecosystem services and biodiversity conservation. One of the threats La Mintzita’s fish community faces is the invasion of two species of poeciliid fishes that are known to be very successful invaders, Xiphophorus hellerii and Poecilia reticulata. The objective of this practice is to make a snapshot fish diversity survey of the viviparous fish species present in La Mintzita’s basin shore, where most viviparous fish concentrate, to evaluate the viviparous fish species richness and abundance, as well as how invaded and/or dominated this community is.


To assess the number of species present in La Mintzita we will use traps and a hand net, and to assess the relationship between number of species and their abundances we will use only the hand net during 60 minutes.



Scoop net
Fall traps

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Con la guía de identificación, identifica las especies a las que pertenecen los peces de las siguientes fotografías. Construye una tabla de especies y abundancias, ajustando las abundancias por especie de acuerdo con el número de individuos que hay por foto. Toma en cuenta que más de una fotografía puede identificarse  con la misma especie. 






The report must include the following sections:


Biodiversity – freshwater ecosystems – native and invasive species – Mexican viviparous fish communities– La Mintzita – Objectives

This section must have relevant in-text references.


  • Field work methods

    • To know the number of species and to asssess its abundances in the community (hand net and fall traps)

  • Data analysis methods (Dominance and diversity indexes)



  • Include a table with númber of species and their abundances

  • Include a rank-abundance graph

  • Calculate the Simpson’s Index value, including the formula path to get it with the numbers gathered from the practice

  • Calculate Shannon’s Index value, including the formula path to get it with the numbers gathered from the practice


Discuss results, including the following points:

  • How even is the distribution of fish species abundances in La Mintzita?

  • How invaded is the site?

  • What do the indices’ values mean in respect to the fish diversity of this community?


Moreno, C. E. (2000). Métodos para medir la biodiversidad. Volumen 1. Manuales y tesis SEA. 





Dr Morelia
Camacho Cervantes

Invasive species and animal behaviour.

 Instituto de Ciencias del Mar y Limnología, UNAM.

Dr. Nicoletta Righini


and nutritional ecology.

Instituto de Investigaciones en Comportamiento Alimentario y Nutrición, Universidad de Guadalajara.

Dr. Ek del Val de Gortari

Invasive species and

biotic interactions.

Instituto de Investigaciones en Ecosistemas y Sustentabilidad, UNAM.

LL.M. Gloria M. Huerta Ramírez


social research

and economic valuations.

Instituto de investigaciones Económicas y Empresariales, Universidad Michoacana de San Nicolás de Hidalgo.

Dr. Roberto Lindig Cisneros

Environmental restoration.  Instituto de Investigaciones en Ecosistemas y Sustentabilidad, UNAM.