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The larvae of the Chilean rock crab were all killed in tests involving recommended doses of lice treatments. Photo: Wikimedia Commons
The larvae of the Chilean rock crab were all killed in tests involving recommended doses of lice treatments. Photo: Wikimedia Commons

Four of the most commonly used anti-parasitics against sea lice proved to be lethal at low concentrations for crab larvae, Chilean scientists said.

In four different experiments, scientists from various Chilean institutions evaluated the effects of cypermethrin, deltamethrin, azamethiphos and hydrogen peroxide on larvae of the Chilean rock crab (Metacarcinus edwardsii), the most important commercially exploited crab in the country.

The study investigated the toxic effects on the larvae (zoea I) of seven different concentrations of the four chemicals mentioned above (based on manufacturers' recommendations (CRM) for the treatment of C. rogercresseyi); and chronic exposure for two weeks to two of these four pesticides.

100 per cent mortality

The experts tried to recreate what happens in the industry when they are carried out in situ treatments with diverse chemical compounds that later can be downloaded to the marine ecosystem.

"The concentrations and exposure times recommended by the manufacturers of the four compounds have a lethal effect on zoea I under acute exposure, producing 100 per cent mortality," explained the authors in their results, and said that all larvae were dead or died after 30 minutes of exposure to cypermethrin and after 40 minutes to deltamethrin at concentrations 100 and 20 times lower than the CRMs.

With respect to the other compounds, azamethiphos affected all larvae at a concentration 10 times lower than CRM and hydrogen peroxide had the lowest detrimental effects, but even so, a 100 per cent mortality rate was observed.

Water column

The scientists concluded that "the parasitic control can cause a greater damage in other species than previously thought. In addition, several centres may be treated in a relatively small area, which increases the potential for repeated or chronic exposure", and "direct lethal effects of pyrethroids (cypermethrin and deltamethrin) on larvae are probably restricted in time and space with respect to the point of application, but the action of azametines may affect a larger area of the water column".

Regarding the effects on plankton and accumulation in the marine sediment of these chemicals, the researchers mentioned that additional studies are needed to understand the implications in the pelagic and benthic communities.

The abstract of the paper entitled " Lethal and sub-lethal effects of commonly used anti-lice formulations on non-target crab Metacarcinus edwardsii larvae ", can be reviewed here.