Lumpfish (Cyclopterus lumpus L.) develop amoebic gill disease (AGD) after experimental challenge with Paramoeba perurans and can transfer amoebae to Atlantic salmon (Salmo salar L.)

Abstract

Cleaner fish such as lumpfish (Cyclopterus lumpus L.) and ballan wrasse (Labrus bergylta A.) are increasingly used to delouse farmed Atlantic salmon (Salmo salar L.). In 2014, >20 million cleaner fish were placed into net-pens with farmed salmon in Norway. Amoebic gill disease (AGD), caused by the opportunistic, parasitic amoeba Paramoeba perurans, is emerging in salmon farming in Northern Europe. The amoeba displays low host specificity as it has been isolated from a range of fish species in addition to salmonids, such as wrasse and lumpfish cohabitating with farmed salmon. It is, however, not known to which degree lumpfish respond to P. perurans challenge, to which extent lumpfish may develop AGD, and if they can function as a vector for the spread of P. perurans to salmon. The present study shows that lumpfish can be infected with P. perurans under experimental conditions and develop AGD. However, lumpfish are more resistant and the development of pathology is slower compared to salmon. It is also shown that lumpfish can act as carriers and transmit parasitic amoebae to Atlantic salmon. Importantly, it is demonstrated that the gill lesion score system extensively used for evaluating AGD in Atlantic salmon is less suitable for lumpfish infected with P. perurans as the disease develops more slowly in lumpfish and because lumpfish may be non-symptomatic carriers. Statement of relevance1)The last few years, lumpfish have been used as cleaner fish in order to delouse farmed Atlantic salmon. However, nothing is yet known about its susceptibility to the parasitic amoeba P. perurans.2)Currently, nothing is known about amoebic gill disease (AGD) development in lumpfish and the possibility that amoeba may be transferred from lumpfish to salmon.3)There is currently little information about the pathology (macroscopic and histological changes) in lumpfish.4)We have found that the commonly used gill scoring system for salmon is not applicable for lumpfish, and we recommend that the lumpfish is screened, not scored before transfer to net-pens with salmon.