Since 2002 a new skin condition in farmed rainbow trout (Oncorhynchus mykiss) in England has been recognised by fish health inspectors. This has became known as puffy skin disease (PSD). In a recent study, PSD was reported on 37% (n=49) of rainbow trout sites, located in 28 river catchments across England and Wales (Peeler et al. 2014). In the water, affected fish appear grey in colour and on closer inspection affected areas of skin, normally on the flank, show excessive mucous and dermal hyperplasia.
In order to elucidate if the PS condition is caused by an infectious agent, 20 naive rainbow trout of between 300-500 g were exposed to PSD by cohabitation with 15 fish collected in the field showing the condition. By 15 days post challenge (dpc) some naive fish started to show irregular ‘flashing’ swimming behaviour. Naive fish showing PS symptoms were sampled at 23 dpc with between 25 to 80% of their skin affected, together with scale loss. The challenge was terminated after 41 days. All of the remaining naive fish sampled at that point, presented with varying degrees of PS-like symptoms, with between 10-60% of their skin surface affected.
The causative agent was not detected by conventional bacteriology, histological or virological analyses. In conclusion, we have initial evidence that PSD is a transmissible disease.
