CBH Group has confirmed half a tonne of canola grain was spilt into Cockburn Sound last month, as Fisheries experts continue to probe why more than 1,500 dead fish have washed up in Perth's south.

CBH Group has confirmed half a tonne of canola grain was spilt into Cockburn Sound last month, as Fisheries experts continue to probe why more than 1,500 dead fish have washed up in Perth's south.