Fish kill blamed on bacteria

A recent fish kill north of Broome was likely caused by local environmental factors which made fish susceptible to a naturally occurring bacterial infection, the Department of Fisheries has confirmed.

The DoF has been investigating a marine fish kill around 70 kilometres north of Broome since March 15.

A member of the public initially reported dead and dying fish on a beach in the Manari area.

Fish deaths were observed along approximately 60 km of coast, north to Cape Bertholet and south to Willie Creek, and also some distance off the Kimberley coast within an algal bloom.

Investigations included aerial, beach and vessel surveys, examination of local environmental factors, and testing and analysis of fish and water samples by specialist laboratories.

Testing included examination of water and phytoplankton samples for the presence of harmful or toxic algal species, and the screening of fish tissue samples for evidence of a broad range of algal and chemical toxins.

Scientists advised that the fish deaths were due to a systemic bacterial infection, which test results later confirmed was caused by the bacteria Streptococcus iniae.

This was consistent with the symptoms seen in dead and dying fish in initial reports.

Streptococcus iniae is a major fish pathogen implicated in fish kills around the world, in both wild and aquaculture fisheries.

The bacterium occurs naturally and is considered opportunistic, with serious infections arising mostly in stressed animals.

Scientists are confident that local environmental factors, including high water temperatures in particular, stressed the fish making them susceptible to the bacterial infection.

The DoF said the environmental factors were also likely to be associated with the observed algal bloom in the region, which tests indicated was not the cause of the fish deaths.

DoF biosecurity section leader, Victoria Aitken said the department greatly appreciates the assistance and support of the local community who provided helpful information throughout the incident.