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Fish in freshwaters of the world. Because freshwater systems often act as a sink for ... fish back into the population, the local proliferation of pest fish species, and clear ...

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Freshwater ecosystems and fish

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freshwater ecosystems and fish
Freshwater ecosystems and fish






Geographic distribution



Human caused Impacts in freshwater fish

Ecological integrity

eduardo d sendra research biologist
Eduardo D. SendraResearch Biologist
  • Fresh water lakes and rivers of central Argentina
  • Biodynamics
  • Ecology of Fish Populations

Institute of Limnology Dr. Raúl A. Ringuelet

Florencio Varela, Buenos Aires, Argentina

the water resource
The water resource
  • Water is needed by all living organisms: plants use it in photosynthesis, humans and other animals drink it, and aquatic plants and animals live in it. Water also plays an important part in many natural and human processes and is a critical component of countless physical and chemical reactions. It also supports many economic activities. Yet freshwater is so common and so abundant, that we rarely give it a thought, that is, until our water supply is threatened or water becomes less fit for our use.
water users
Water users
  • Humans use about half disposable surface water. These needs are for agriculture, electricity, industry, sewage and sanitation, fisheries and aquaculture. The other half is for nature to use for sustaining biodiversity and ecological functions. It is thought that by 2025 human will probably be using about ¾ of disposable surface water.

Nature organizes life in ecosystems, communities of organisms and the environment functioning together as a whole. A pond or a coral reef is good examples.

analytical viewpoints
Analytical viewpoints
  • Man for practical reasons has decided to artificially subdivide ecosystems in components or categories. Terrestrial, freshwater or marine are examples. Producer and consumer organisms are subdivisions taking in account other criteria.
ecology considerations
Ecology considerations

Surface waters sustain freshwater biodiversity (FB) and ecological functions (EF) while serving for human needs.

FB benefits: Fisheries, Aquaculture, Recreation, Crops, Medicines. FB importance: 25 % of Phyla are found in freshwaters. 40 % of the fish are from freshwaters.

Geographic distribution of organisms is uneven. For fish species from temperate regions it is lower than for tropical regions. Three richest areas: northern South America, central Africa and Southeast Asia (RAINFORESTS).

Threats to FB: habitat loss (agriculture, forestry, dams and urbanizations), Pollution, Introduction of exotic species and over harvesting. Main effects are responsible for modification of hydrological cycle. Erosion, flooding, siltation.

EF from different processes: i.e. Nitrogen fixation, habitats, oxygen generation, and recycling of nutrients.

landscapes and catchments
Landscapes and catchments
  • Lentic ecosystems are in negative landscapes.
  • Lotic systems mainly conduct production to lentic systems or to the ocean.
  • Terrestrial are in positive escapes.
sustainability of the resources
Sustainability of the resources
  • Surface waters sustain freshwater biodiversity and ecological functions while serving for human needs.
  • All human activities will impact on the environment
environmental impact assessment
Environmental Impact Assessment
  • It is a management decision to set thresholds acceptable to society. Environmental impacts usually lie within the realm of science to determine and the discipline that determines the probability of negative impacts to the environment is called ecological risk assessment.
  • Three components make up EEA:

Chemical criteria, Laboratory toxicity bioassays and Environmental effects monitoring.

fish in freshwaters of the world16
Fish in freshwaters of the world
  • Because freshwater systems often act as a sink for contaminants, receiving a variety of anthropogenic compounds from both point and non-point sources, we chose to study fishes, as they represent the species most likely to be exposed to contaminants. Methods in order to evaluate potential adverse effects of pollution on fishes in their natural environment are needed.
what are the risks
What are the risks
  • Assessment of environmental effects can be performed at different levels of biological organisation. As a general rule, as biological organisation increases in complexity, the environmental relevance increases. These results in a higher level of uncertainty linked to the complexity of the systems. As the level of biological complexity decreases it is easier to attribute the cause of the observations that are being made.
main problems to fish
Main problems to fish
  • Runoff from agriculture: pesticides, fertilizers, manure, and sediments.
  • Runoff from urban areas: municipal and industrial discharges.
  • Dams block migrations and change flows and temperatures.
  • complete absence of a keystone fish species
  • complete failure to recruit young fish back into the population
  • local proliferation of pest fish species
  • clear signs of over fishing
impacts observed in freshwater fish
Impacts observed in freshwater fish

At those sites where pollution impacts are known to exist, one may observe changes in a number of biological and chemical indicators of pollution stress. Less obvious is as the presence of a number of potentially serious impacts on fish populations. Such observations included the complete absence of a keystone fish species, complete failure to recruit young fish back into the population, the local proliferation of pest fish species, and clear signs of over fishing. Recent research has led to the hypothesis that thermal pollution, or elevations from natural temperature, could have dramatic effects on biodiversity because these changes greatly favour a number of warm water pest species.

ecological integrity
Ecological integrity
  • Maintaining livestock density in the watershed ; along with sewage and agricultural runoffs control phosphorous imports.
  • Protecting healthy wetlands nearby for control of nutrient oversupply.
  • Maintaining riparian areas with forests and grassland, control erosion and attenuate nutrient inputs.
  • Making periodic regulated extractions of natural production to prevent eutrophication (fisheries, aquaculture, etc.)
  • Maintaining healthy indigenous biological communities (no introductions).
  • Taking a more spiritual and less materialistic viewpoint at nature and agriculture.

Integrity to maintain adaptive communities with biological or functional organizations comparable to natural unpolluted waters of the area.Thank you for your attention.