Farmer loses 5000 fish after the use of chemicals in fishing

How a farmer lost over 5000 fish due to chemicals normally used during fishing

Mkulima today farmers are faced with different challenges from every angle. With the aim of boosting production during this period when fish populations are declining some farmers have been using unconditional methods. Farmer loses 5000 fish after the use of chemicals in fishing.

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Use of chemicals in fishing

While it might lead to better production and earnings it comes with negative effects on the fish population and the consumers.

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Kenya is endowed with various aquatic resources from the lakeside to the highlands and ocean.

Species of fish available in these resources include but not limited to

  • Trout
  • Tilapia
  • Mudfish

Before setting up that pond you have dreamt of all your life make sure

  • The land has a slight slope of about 11 percent
  • Steep slopes aren’t ideal since most of the water might flow away

The use of chemicals in fishing is illegal in several countries but remains to be one of the most used methods of fishing globally.

The system is used because of its quick ability to capture large quantities of fish to meet the high demands of the market.

As a result of poor enforcement and unavailability of simple, fast, and cost-effective chemical confirmatory test methods.

The technique poses serious dangers to fishermen, consumers, and the environment due to its effects on non-targeted organisms and indiscriminate killing of the targeted population.

Risks of use of chemicals in fishing

The use of chemicals in fishing pose huge risks to the health of the consumer like you and I.

Some of the chemicals used in fishing include sodium/potassium cyanide, gun powder, pesticides such as DDT (Dichlorodiphenyltrichloroethane), carbide, powdered detergents, petrol, and diesel, and plant extracts like rotenone.

Chemical fishing is destructive. For the sake of cyanide, it discolors and destroys coral reefs while DDT has the ability to accumulate in the fish and passed on to the consumer threatening their health.

In one case a farm manager reported to one of the vet labs that all their over 5000 fish in their pond had died overnight.

An investigator confirmed the huge losses with all the fish floating on one end of the large fish pond and was used for tilapia fish farming for a period of five years.

The clinical history of the case was that the fish were active and healthy on Sunday through Monday but were found dead on Tuesday morning.

As a result of a pump failure, they had been unable to pump water from the borehole into the fish pond.

Immediately the lack of oxygen (anoxia) or poisoning was suspected for the cause of death. The next thing to check was if the deaths were accidental or intentional.

The team investigated some of the dead fish, fish feed, and the water from the pond. They took their own samples plus those that were provided by the farm manager. They also poured some of the water on the grass to test for herbicides.

After some time there was no effect on the grass an indication of luck of herbicides in the pond water and the post mortem on the fish didn’t indicate anything either.

Flies were buzzing on the dead fish an indication that the cause of death was not as a result of an insecticide and the greenish coloration on the pond was as a result of algae growth.

Aflatoxin

The aflatoxin B1 level in the fish feed was 43.72ppb which is above the maximum allowable limit of 10ppb in animal feeds but lower than the tolerable levels of 100ppb for tilapia.

Aflatoxin, therefore, was ruled out as the cause of death for the fish.

Oxygen

The dissolved oxygen (DO) in the water was between 0.25mgl-1 and 3.25mgl1 but tilapia can tolerate DO levels of as low as 0.3mgl-1.

The conclusion is the DO levels might have caused the deaths but it is not the reason for the 100 percent mortality rate experienced in the pond.

No organophosphates were detected in the water, but a cyanide level between 2.48mg/100ml and 4.43mg/100mls (24.8-44.3mg/l) in the water was detected.

Cyanide levels of 0.01-0.02mg/l are normally lethal to fish. Although the investigations did not identify the culprit, it was concluded that having used a chemical that is used during fishing was the cause of death of the fish population.

It was concluded that the death was a result of an overdose of cyanide. This might have been facilitated by the lack of freshwater into the pond as a result of the farmer’s pump breakdown during the weekend.

The tests served as a reminder that fish require high water quality with consistent parameters such as

  • DO
  • Turbidity
  • Color intensity
  • Temperature
  • pH and others that affect their growth and survival.

Other materials that are not harmful to the fish like feeds and fertilizers normally affect the quality of the water and therefore should be well managed.

Take care of the items used on your farm in order to avoid losses not only the use of cyanide but also others like sodium metabisulphite that is used in meat preservation in the country.

Credits: Dr. Mwirigi

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