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Scientist from Fera Science identifies current threats to freshwater fish

Freshwater fish are the most endangered group of animals on the planet, with more than a third of species at risk of extinction. Dr Rachael Benstead, senior aquatic ecotoxicologist at translational science and research organisation, Fera Science Ltd. identifies the current threats to freshwater fish.

The International Union for Conservation of Nature (IUCN) estimates that out of the 45 per cent of all fish species found in freshwater habitats, 200 of the 522 (38 per cent) of European freshwater fish species are threatened with extinction and 12 are already extinct.

Humans are hugely dependant on fish populations for food and income. In Africa alone, more than 7.5 million people rely on freshwater fish for both nutritional and monetary sustenance. Yet, it is human activity that is threatening fish populations the most with overfishing, pollution and construction.

Construction

Construction projects, such as canals, roads and dams, cause blockages that were not in place previously. A paper published in Science in 2016, explored the unprecedented boom in construction of hydropower dams in the world's most biodiverse river basins. The Amazon, Congo and Mekong contain one third of the world's freshwater fish. While the planned construction of 450 new dams will meet the need for clean energy generation, has the impact on freshwater biodiversity been considered?

The authors of this paper propose that in order to maximise societal benefit and minimise environmental degradation, more comprehensive and rigorous impact analyses must take place prior to commissioning a new dam, not only to protect fish populations, but to lessen the effects of economic losses faced by communities.

Food sources

Pollution comes in many forms, including detergents, food processing waste and chemicals. However, it's not necessarily the direct exposure of pollutants to fish that can cause population depletion, but the exposure to their main food source — invertebrates.

If invertebrate populations have been reduced or even eradicated from a habitat due to pollution, this can have detrimental effects on the entire ecosystem. Therefore, freshwater invertebrates play a direct role in fish wellbeing, and one that needs to be carefully considered.

Under pressure

As the agricultural sector aims to meet growing food demand, there is a heavier reliance on plant protection products to defend plants from pests, often near to aquatic habitats. This could reduce invertebrate populations, and in turn freshwater fish populations, if the product isn't applied as per label instructions.

Additionally, an increased use of pesticides furthers problems of resistance, meaning more products will need to be brought to market to replace redundant alternatives. But, fundamentally pesticides must be assessed effectively, but fairly, to protect freshwater populations and to ensure the industry has a safe selection of products available.

Fera, in partnership with the Centre of Crop Health and Protection (CHAP) and Innovate UK recently launched the E-Flows mesocosm, Europe's largest and most advanced, fully flow-through mesocosm.

This outdoor experimental system allows research to take place on invertebrates (and aquatic plants) in highly realistic conditions, due to the large water volume it can support and its fully flow-through capabilities. This means the effects of pesticide exposure on invertebrates can be predicted, and, in turn, freshwater fish can be protected.

While freshwater fish are the most endangered group of animals on the planet, it's important to consider the entire ecosystem, including invertebrates, when predicting the effects of construction and pollution. As the global hydropower boom continues, and demand in agriculture increases, effective research will remain vital to predict effects to aquatic populations.

For more information on the E-Flows mesocosm, or to register to use these facilities, e-mail david.phillips@fera.co.uk.

For further information about Fera contact: Claire Boston-Smithson, Fera Science, National Agri-food Innovation Campus, Sand Hutton, York YO41 1LZ

Telephone: +44 (0)1904 462227

www: www.fera.co.uk/

e-mail: claire.boston-smithson@fera.co.uk

Twitter: https://twitter.com/FeraScience

LinkedIn: https://www.linkedin.com/company/fera-science