The latest mass escape from a B.C. fish farm has led to renewed calls from the NDP to change how the farms are run.

About 40,000 Atlantic salmon escaped last Friday from a Marine Harvest Canada farm off the northern tip of Vancouver Island.

The NDP is demanding the Liberals replace open net pens with closed containment systems to protect wild salmon from fish farms but Agriculture Minister Steve Thomson won't make any commitments.

He says the government takes the escape very seriously and will investigate fully.

NDP environment critic Rob Fleming also demanded that Thomson promise not to issue more fish farm licences before B.C. gives up jurisdiction over the farms to the federal government next February.

Thomson wouldn't make such a promise, saying B.C. retains the right to regulate the farms until February.