Journal of Fish Diseases: Vol 37, Issue 8 (August 2014) Seasonal increase in sea temperature triggers pancreas disease outbreaks in Norwegian salmon farms
A STENE; BB JENSEN; O KNUTSEN; A OLSEN; H VILJUGREIN Pancreas disease (PD) is a viral disease causing negative impacts on economy of salmon farms and fi sh welfare. Its transmission route is horizontal, and water transport by ocean currents is an important factor for transmission. In this study, the effect of temperature changes on PD dynamics in the
fi eld has been analysed for the fi rst time. To identify the potential time of exposure to the virus causing PD, a hydrodynamic current model was used. A cohort of salmon was assumed to be infected the month it was exposed to virus from other infective cohorts by estimated water contact. The number of months from exposure to outbreak defi ned the incubation period, which was used in this investigation to explore the relationship between temperature changes and PD dynamics. The time of outbreak was identifi ed by peak in mortality based on monthly records from active sites. Survival analysis demonstrated that cohorts exposed to virus at decreasing sea temperature had a signifi - cantly longer incubation period than cohorts infected when the sea tem- perature was increasing. Hydrodynamic models can provide information on the risk of being exposed to pathogens from neighbouring farms. With the knowledge of temperature-dependent outbreak probability, the farmers can emphasise prophylactic management, avoid stressful operations until the sea temperature is decreasing and consider removal of cohorts at risk, if possible.
Aquaculture International: Vol 22, Issue 4 (August 2014) Effect of oxidation-reduction potential on per- formance of European sea bass (Dicentrarchus
labrax) in recirculating aquaculture systems X LI; JP BLANCHETON; Y LIU; S TRIPLET; L MICHAUD The direct impact of oxidation-reduction potential (ORP) on fi sh welfare and water quality in RAS is poorly documented. Here, the effects of the fi sh size (S-1, S-2, S-3) and ORP level on the performance of European sea bass (Dicentrarchus labrax) were investigated. Three size fi sh were distributed into two RAS (RAS and RAS O-3). Ozone was injected into RAS O-3 to increase the ORP level. The ORP was stabilised to four successive levels: 260-300, 300-320, 320-350, and 300-320 mV in fi sh tanks during four periods (P1-4). At the last day of each period, the hematological parameters, plasma protein and mortality of sea bass were analysed. Two-way ANOVA revealed that several hematological parameters, including pH, hematocrit, concentrations of oxygen, carbon dioxide, glucose (Glu), ionized calcium, kalium, and hemoglobin, were signifi cantly infl uenced by the increased ORP levels over the experimental period. The alteration in blood Glu and plasma protein concentration showed that ORP around 300-320 mV started to stress sea bass. Once the ORP exceeded 320 mV in the tanks during the P-3 period, mortality occurred even when total residual oxidants/ozone-produced oxidants was only 0.03-0.05 mg L-1 in the fi sh tanks. At the same time, plasma protein decreased notably due to appetite depression. After the decrease in ORP during the P-4 period, mortality continued. In conclusion, the results strongly suggest that for European sea bass in RAS, the ORP should not exceed 320 mV in the tanks. Once ozonation damaged fi sh, the effect seemed to be irreversible. However, how ORP affected related hematological parameters still need the further investigations. FF
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