Delousing agent kept juvenile lobsters from finding shelter

Teflubenzuron is sometimes added to the feed of farmed salmon to treat sea lice infestations. The Institute of Marine Research has found traces of the chemical on the sea bed around fish farms, and it is therefore investigating how teflubenzuron affects other crustaceans, such as lobsters.

“If lobsters consume teflubenzuron through their food for an extended period, they develop stiff joints and antennae after changing their shell. They appear to get a kind of arthritis and find it difficult to walk around”, says marine scientist Ann-Lisbeth Agnalt.

In a recent experiment, scientists placed juvenile lobsters in an oblong tank with a shelter at the far end. They timed how long it took the lobsters to find the shelter and enter it. 19 lobsters were given feed containing teflubenzuron until two weeks before the experiment, and 19 had a normal diet (the control group).

Took small steps forwards and backwards

In the first run, the control group spent just over five minutes to take shelter on average. The lobsters given delousing agent spent over 18 minutes. Two never even found the shelter.

“The lobsters in the control group used their antennae to feel their way along the wall. They explored the whole space, found the shelter and walked straight in”, explains Alessandro Cresci, main author of the newly published article.

“But the lobsters on the diet containing delousing agent didn’t use their antennae actively in the same way. They took a few small steps forwards, before repeatedly turning around and going back to the starting point. They struggled to identify the shelter, entering it and exiting it again before finally settling down.

Practise didn’t make perfect

All of the lobsters were quicker when made to repeat the task, but even the third time around there was a significant difference between the two groups. 

A reduced ability to find shelter may affect the survival rate of lobsters, because it makes them more vulnerable to predators.

Relevant doses

In the experiment, the juvenile lobsters were fed teflubenzuron in concentrations that are found in the natural environment for a period of eight weeks. 

“Salmon are treated for seven days at a time, but salmon faeces and waste feed remain on the sea floor, so lobsters and other animals may continue to consume teflubenzuron for much longer. Teflubenzuron has been found on the seabed 1,100 metres away from fish farms”, says Ann-Lisbeth Agnalt. 

However, the researchers cannot say for sure whether the behaviour of the lobsters would have been the same in their natural environment. This is because they are simply unable to find juvenile lobsters in the wild.

“We don’t know where they are and how they live. The specimens used in the experiment are thus what we call ‘naïve animals’. We hatched them, and we cannot say for certain whether they behave in the same way as wild juvenile lobsters. But we must assume that the effects of teflubenzuron on their bodies are the same.

Harmful even when there are no visible effects

The experiment is part of a larger investigation of the impact of teflubenzuron on the European lobster. Several lobsters died during their exposure to teflubenzuron. The 19 that took part in this experiment were the ones that survived and which appeared to be physically fine. In other words, the scientists were measuring the “sublethal effects” – those that are not fatal. 

“We have done quite a bit of research on fatal doses for lobsters, but much less on how the lobsters that survive are affected. These important findings support the new limits on the use of teflubenzuron”, says Agnalt. (See fact box.)

“The effects of delousing chemicals on behavior, spatial orientation and cognitive abilities could involve several species living on the sea floor. We are therefore investigating the potential impacts of these chemicals in the wild”, her colleague Alessandro Cresci adds.

The institute of Marine Research is devoting more research into the effects of delousing chemicals in nature. See also: Hva vet vi om hydrogenperoksid (article in Norwegian)

Reference

Cresci, A., Samuelsen, O. B., Durif, C. M., Bjelland, R. M., Skiftesvik, A. B., Browman, H. I., & Agnalt, A. L. (2018). Exposure to teflubenzuron negatively impacts exploratory behavior, learning and activity of juvenile European lobster (Homarus gammarus). Ecotoxicology and environmental safety, 160, 216-221. https://doi.org/10.1016/j.ecoenv.2018.05.021