Up to 50,000 infected fish have been slaughtered and movement restrictions have been put in place along the River Ouse catchment area in Yorkshire.

The outbreak of viral haemorrhagic septicaemia (VHS) at the trout farm in the Yorkshire Dales is being investigated by Defra scientists.

Fish farms in the area and others which may have had contact with the infected premises have been inspected.

No human risk

But none so far have shown evidence of disease, officials said.

The affected farm has been cleared of all fish and plans are in place to disinfect the site.

VHS affects mainly farmed rainbow trout and can cause up to 80% death rate.