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Pesticides Killing Fish: A Sad “Tail”


Want to learn more about the importance of sourcing food from ethical and sustainable sources? Start doing so today, by equipping yourself with the knowledge about pesticides killing fish...

Every year, millions of fish in fish farms, lakes, rivers, and seas are killed by pesticides. These slippery friends die from pesticides if they’re applied to the land, but mostly from rainfall, causing the pesticides to drift downhill towards water streams.

The economic value of these fish, which are killed annually by pesticides, has now reached £8 to 21 million! What’s more, with the difficulty of tracing these deaths, this number is most likely underestimated.

At the Leisure F&B Expo, we want to keep those within the food industry informed on the latest issues, providing tips for future reference. That's why we offer FREE tickets to our show; to make sure all food and beverage coorindators, from all sectors, can stay in the loop! This August has been the home of International Fishing Month, so what better time to inform you of the problems with pesticides killing fish, and what we can do about it.

A pile of colourful sardines lined up side-by-side, lying still with their eyes open

Why are Pesticides a Problem For Fish?

Yes, pesticides can cause fish deaths, in large quantities. That said, it’s not just deaths that are caused. In fact, with prolonged, but minimal, exposure, the effects on fish can be noticeable.

A biological opinion drafted by the National Marine Fisheries Service (NMFS) in 2012, was shown to the Environmental Protection Agency (read more about this, from the EPA, here). It concluded that agriculture herbicides—oryzalin, trifluralin, and pendimethalin—pose a direct threat to around 50% of some endangered fish species. These include the Puget Sound steelhead species and Pacific salmon.

Not only this, but these herbicides will directly affect their habitat, which can cause biological changes in the fish. For example, the inhibition of certain enzymes within the fish can cause a delay in their growth (click here to read about these biological changes). Generally, this can cause major problems within the food chain, as well as in the economical value of fish.

Symptoms of Pesticide Poisoning

1. Lethargy.

2. Loss of equilibrium, or inability to maintain an upright position.

3. Hemorrhaging in dorsal fin muscles, which look a dark-reddish colour.

4. Hypersensitivity, with uncoordinated movements, perhaps erratically moving in a circle.

5. Tremors or convulsions.

6. Involuntary pectoral fins or opercula extension.

7. Curvature of the spine.

8. Death.

The most common cause of death in fish is a DO (dissolved oxygen kill), where a lack of dissolved oxygen in the water causes them to suffocate. With deaths like these, larger fish will die off first.

However, with pesticide exposure, it’s the smaller fish that will die off first, which is a good way to identify these deaths. What’s more, other semi-aquatic animals, that don’t rely on dissolved oxygen to survive, will die from pesticides too. For example, birds, frogs, turtles, invertebrate insects, crabs, and shrimp may be affected.

Otherwise, though, death is almost undetectable, as the water will remain normal in colour and odor, compared to with DO deaths.

Fish bones against a black background, which looks as though it's swimming

How to Prevent Pesticides Killing Fish

There are a number of alternatives methods to pesticides, which could be a better avenue to endorse, when purchasing within the food industry.

Natural Pesticides and Insecticides

Natural oils can be a great, natural method of protecting your plants, without harming the environment. A cheap plant spray consists of a simple mixture of essential oils, lemongrass, and citronella.

This method can be used in home gardening, and agricultural, large-scale farming. Just test a section of your plants before spraying them all, to make sure they don’t burn, and this could be your new best friend.

Biological Pest Control

This can be done in two ways:

  • By using bacteria in the soil to control pest behaviour.

  • Utilising natural predators to ward off pests.

The latter is the much more common method of doing this. It’s mainly done through trap plants, or companion planting, which is the method of increasing biodiversity in a specific area of your plot of land to lure pests away from your agricultural plants. For example, by planting more nectar-producing flowers, which attract pollinators, these work as fantastic predators for the smaller pests which destroy.


A really brilliant method, which has recently been established, is using a drone to spot wasted crops. By targeting the areas where plants are becoming damaged by pests or animals, farmers won’t have to spray pesticides all over their field, but just specifically targeted areas.

Crop Rotation

This is a pretty well-established method of farming. However, it can really help with reducing pests, too. By getting the pests used to feeding on certain plants, and then moving the plants around, they will attempt to travel to the other plants, most likely dying on the way!

A dead fish lying in a pond from pesticides, with lots of weeds and bracken surrounding it

What to do if You Think Pesticides are Killing Fish

The first thing to do? Notify the Department of Pesticide Regulation (DPR), or alternative organisation, immediately.

Things to Note, and Tell the DPR

1. Time of day the deaths began.

2. Types and sizes of fish present.

3. Number of fish killed.

4. If there have been fish deaths in adjacent bodies of water.

5. If fish kills have happened before in the same body of water.

6. If you think you’ve witnessed the use of pesticides near the water source.

7. The weather conditions at the time of the fish kill, and over the past 24 hours leading up to this.

8. For fish production ponds: the number of fish in the pond, what and how much they’re being fed, and when it was stocked.

By alerting the correct authorities, an investigation can be put forth to decide the source of the pesticides, and tests can be done. Water conditions change rapidly, and modern pesticides won’t last long in the water source. Once measurements are taken, the pH can be stabilised quickly, hopefully reducing further losses.

Dead fish from pesticides, lying on the sand, completely motionless

Something Fishy is Going on...

It may seem as though there’s a lot to take into account when it comes to pesticides killing fish. That said, these facts and figures are important, especially when you’re part of the food and agricultural world.

If you’re looking to explore the world of sustainable products, come along to our Leisure F&B Expo, for absolutely FREE!

Otherwise, perhaps you have a food product which sources fish, keeping pesticides in mind? The Leisure Food and Beverage Expo on 6th-7th November 2019, at the NEC Birmingham, will be a great platform to showcase what you offer, at an exhibitor stand. Our Event Director, Oliver Hayes, would be more than happy to set you up with a stand, so email, or call +44 (0)117 929 6087 to get involved.

Become part of the largest exhibition of its kind in the UK!

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