• Gill damage to Atlantic salmon (Salmo salar) caused by the common jellyfish (Aurelia aurita) under experimental challenge

      Baxter, E.J.; Sturt, M.M.; Ruane, N.M.; Doyle, T.K.; McAllen, R.; Harman, L.; Rodger, H.D. (PLoS ONE, 2011)
      Background: Over recent decades jellyfish have caused fish kill events and recurrent gill problems in marine-farmed salmonids. Common jellyfish (Aurelia spp.) are among the most cosmopolitan jellyfish species in the oceans, with populations increasing in many coastal areas. The negative interaction between jellyfish and fish in aquaculture remains a poorly studied area of science. Thus, a recent fish mortality event in Ireland, involving Aurelia aurita, spurred an investigation into the effects of this jellyfish on marine-farmed salmon. Methodology/Principal Findings: To address the in vivo impact of the common jellyfish (A. aurita) on salmonids, we exposed Atlantic salmon (Salmo salar) smolts to macerated A. aurita for 10 hrs under experimental challenge. Gill tissues of control and experimental treatment groups were scored with a system that rated the damage between 0 and 21 using a range of primary and secondary parameters. Our results revealed that A. aurita rapidly and extensively damaged the gills of S. salar, with the pathogenesis of the disorder progressing even after the jellyfish were removed. After only 2 hrs of exposure, significant multi-focal damage to gill tissues was apparent. The nature and extent of the damage increased up to 48 hrs from the start of the challenge. Although the gills remained extensively damaged at 3 wks from the start of the challenge trial, shortening of the gill lamellae and organisation of the cells indicated an attempt to repair the damage suffered. Conclusions: Our findings clearly demonstrate that A. aurita can cause severe gill problems in marine-farmed fish. With aquaculture predicted to expand worldwide and evidence suggesting that jellyfish populations are increasing in some areas, this threat to aquaculture is of rising concern as significant losses due to jellyfish could be expected to increase in the future.
    • Histological examination of the gills as a method of detecting asymptomatic carriers of A. Salmonicida in Atlantic salmon (Salmo salar)

      McArdle, J.F.; Dooley-Martyn, C.; McKiernan, F. (European Association of Fish Pathologists, 1986)
    • Management and control of proliferative kidney disease (PKD) in a freshwater Atlantic salmon (Salmo salar L.) farm in Ireland: a case history

      Quigley, D.T.G.; McArdle, J.F. (Fish Veterinary Society, 1998)
      During July 1992, an acute clinical outbreak of proliferative kidney disease (PKD) was experienced in two strains (‘Irish’ and ‘Norwegian’) of juvenile (age 0+) Atlantic salmon (Salmo salar L.) held at two adjacent freshwater sites on the River Lee in southern Ireland. Various management strategies (including reduced stocking densities, handling, feeding rates and increased oxygenation), and treatment regimes (involving malachite green and fumagillin DCH) were used to control the disease. A total of 1·3 million juveniles died during the PKD outbreak, representing 61·6% and 54·6% of the Norwegian stock at the two farms respectively. The Irish stock appeared to be more resistant to the disease and only 15·6% died. The weekly prevalence of PKD fluctuated throughout the summer but seemed to disappear by mid-August. Although PKD was detected again during 1993, no clinical outbreak occurred. In conjunction with the management strategies adopted in 1992, seven consecutive weekly prophylactic bath treatments with malachite green (1·6 ppm for 40 minutes) administered prior to mid-July appeared to control the disease. During August 1993, a ten day course of fumagillin (6 mg/kg bodyweight per day) reduced the prevalence of the PKD parasite in a trial batch of juveniles from 24% to zero. The results of this study demonstrated the effectiveness of various management strategies and treatment regimes in controlling PKD.