Norwegian institutes chlorinate salmon river Driva to remove gyro-parasites: “Good effect”

Salmon markingPhoto: Gorm Kallestad / NTB

A major experiment with chlorine treatment of the river Driva got rid of all the parasites on the fish. 

The entire stretch of river of just over 20 kilometers from the fishing barrier and out to the fjord was treated in the second half of August. The Norwegian Institute for Water Research (Niva) was in charge of the assignment, together with the Norwegian Institute for Natural Research (Nina) and the Veterinary Institute in Oslo and Trondheim.

The purpose of the experiment was to find out if chlorine could replace the more toxic rotenone, which – in addition to killing the parasites – also kills all fish in the rivers. 

According to the Norwegian Salmon Rivers Association, the amount of chlorine required is lower than the amount added to waterworks to disinfect drinking water in Norway.

The experiment showed that the salmon was not harmed. But chlorine is toxic to fish and other life in the rivers in high concentrations. Therefore, it is very important to measure the actual chlorine concentration in the river water during treatment.

All the parasites were gone

In the main river Driva, fishing vessels with gyro-infected salmon had been released. Before starting the dosing, the total infection on these fish amounted to 21,000 parasites. 

After a week of treatment, the number was reduced to 110 parasites, and after 11 days, no parasites were detected on the fish at all, according to a press release from Niva.

“We are very pleased to see that we got such a good effect against the parasite down the entire river course, even with some days where the chlorine concentration was lower than desired due to high water flow and demanding conditions. This tells us that the method is perhaps even more robust than we envisioned,” Tobias Holter (Nina) noted.

General test

This year’s chlorine treatment is described as a general test before full-scale eradication treatment, where the main goal was to test logistics, equipment, and dosage effects.

“We look forward to reporting to the Norwegian Environment Agency and hope and believe that this year’s experiences are important in the fight against Gyrodactylus salaris,” project manager Anders Gjørwad Hagen (Niva) stated.

The fight against the parasite in Norwegian rivers has been going on for a long time. In total, the parasite has been detected in 50 Norwegian rivers, but today only the Drivavassdraget and Drammensvassdraget are infected among the large watercourses.

Source: © NTB Scanpix / #Norway Today / #NorwayTodayNews

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