A fisherman rows a boat in the bay of Melinka, about 1200 km (754 miles) south of Santiago, March 24, 2008. The main source of income in Melinka, an island in the Aysen Region, is from the salmon industry and harvest of sea urchins. REUTERS/Ivan Alvarado

SANTIAGO (Reuters) - Salmon producers in Chile, under pressure from international buyers to reduce the amount of antibiotics they put into their fish, intensified their use of the substances in 2015 from the previous year, government statistics showed on Friday.

The government, under legal pressure from environmental groups, also published the amount of antibiotic use per company for the first time ever in its annual report, revealing significant differences between producers operating in the world’s No. 2 salmon exporter.

The new statistics could heap pressure on Chile’s salmon industry, which faces calls to clean up its environmental act and has suffered huge losses in 2016 due to algal blooms.

According to the report, preliminary figures show the proportion of antibiotics to tonnes of salmon produced increased to the highest levels since at least 2007, even though the total amount of antibiotics dropped to 557,200 kilograms (1.23 million pounds) in 2015 from 563,200 kilograms (1.24 million pounds) in 2014. Salmon production was down, which accounts for the higher proportion.

Among large seafood companies, Australis Seafoods reported the most intense use of antibiotics, using 1,062 grams per metric ton of fish. Cermaq, owned by Japan’s Mitsubishi Corp, reported the lightest use, with 391 grams per metric ton.

Last year, Reuters revealed that high antibiotic use among Chilean salmon producers was driving some U.S. retailers, including Costco Wholesale Corp, to turn to antibiotic-free Norwegian salmon.

This year, a massive red tide algal bloom and subsequent disruptive protests from disgruntled fishermen, have caused hundreds of millions of dollars in additional losses.

The publication of antibiotic use per company comes nine days after environmental group Oceana won a suit against Chile’s fisheries regulator demanding that such information be made public.

In addition to Australis and Cermaq, Chilean companies AquaChile, Blumar, Camanchaca, Multiexport Foods, Invermar, and the local unit of Norway’s Marine Harvest have salmon farming operations in the nation.