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Possibility of disease control by ambient dissolved oxygen level Masashi Maita Tokyo University of Marine Science and Technology Japan Counter measures against infectious diseases in Aquaculture Food safety issues by drug residues Chemotherapy Vaccination Probiotics Feed additives Concept of disease outbreaks in farmed fish Host Vaccination Feed additives Probiotics Etiologic agent Environment DO levels Disease outbreaks (Snieszko, 1974) Hypoxia and infectious diseases • Hypoxia (including Low Oxygen uptake by gill damage) are extremely common in aquaculture systems. • Low dissolved oxygen in water has brought high mortality due to infectious diseases. (Fukuda et al. 1997; Walter & Plumb 1980; Mqolomba & Plumb 1992; Caldwell & Hinshaw 1995). Author and year Finding Fukuda, Maita et al. 1997 Influence of dissolved oxygen concentration on mortality of yellowtail experimentally infected with Enterococcus seriolicida Scapigliati et al.,1999 Hyperoxygenation of sea water resulted in a two-fold increase of immunoglobulins of sea bass compared to running seawater. Barton, 2000 Hypoxia is strong enough to alter homeostatsis of fish, more energy in fish body might be allocated for maintain integrity and less will be remain for immunity Boleza et al.,2001 Hypercapnic hypoxia compromises bactericidal activity of fish anterior kidney cells against opportunistic environmental pathogens Cecchini and Saroglia, 2002 Specific antibody response of sea bass against human-γglobulin was reduced after hypoxia exposure than fish in hyperoxia or normoxia Welker et al., 2007 Sub lethal hypoxia compromises immune response of channel cat fish and increase susceptibility to Enteric septicemia Choi et al., 2007 Acute hypoxia compromises immunity of fish In human, it is well known that the oxygen-dependent bactericidal activity plays an important role to protect from bacterial infection (Johnston et al. 1975) and decreased environmental oxygen inhibits the NBT reduction activity, production of reactive oxygen species and the respiratory burst of leukocytes (Jarstrand et al. 1989; Gabig et al. 1979). Objective of this study To investigate the effects of Hypoxia , Hypoxia –reperfusion on mortality and immune response in fish and find the possibility of disease control by ambient oxygen management. Notify: In this study Hypoxia is defined as “low oxygen level (50% DO saturation) where no physiological or behavioral changes could observe” HDO tank LDO tank 110~120% DO-saturation 40~50% DO-saturation Challenged with pathogens Challenged fish and non-challenged fish were cohabited in same tank. Cumulative mortality (%) 110~120% DO-saturation 40~50% DO-saturation c 20 c 15 b 10 5 0 a Non-challenge Challenge In HDO In HDO Challenge In LDO Non-challenge In LDO Mortality due to experimental challenge in LDO was significantly higher. Horizontal transmission was easy to occur in moderate hypoxic condition. 110~120% DO-saturation 40~50% DO-saturation All groups of fish were challenged with pathogens H-H L-H H-L L-L L-L: ■ H-L: ● L-H:□ H-H: 〇 Mortality of infected fish that were transferred to the hyperoxic condition were significantly lowered. Infected fish reared in hypoxic condition would cause high mortality but the mortality could lowered by transfer to hyperoxic condition. HDO tank LDO tank 110~120% DO-saturation Decrease 40-50% saturation 40~50% DO-saturation Challenged with pathogens Increase 40-50% saturation Both group of fish were reared at normoxic tank (80~90% saturation). Survival rate (%) 100 80 Control 60 LDO before challenge HDO before challenge 40 20 0 0 5 10 Days after challenge If the dissolved oxygen level after infection maintain higher than acclimated level, the mortality could be decreased. Partial pressure of venous blood oxygen tension (mmHg) 60 50 40 30 HDO LDO 20 10 0 0 10 20 30 40 50 Days The partial pressure of venous blood were decreased by hypoxic condition and were acclimated by 2 weeks. Phagocytic activity In HKL 100 (%) 80 60 40 20 0 HDO LDO ** 0.1 Reactive oxygen production in HKL (O.D. at 540 nm) 0.08 0.06 0.04 0.02 0 HDO LDO The partial pressure of venous blood oxygen (mmHg) 70 60 50 control LDO 40 30 20 10 0 0 10 20 30 Days 40 50 Cumulative mortality of rainbow trout challenged with Vibrio anguillarum 100 Cumulative mortality (%) LDO→HDO LDO→LDO 80 control 60 * 40 20 0 0 5 Days after the challenge 10 Recommendation • The dissolved oxygen levels in rearing water should monitor frequently to know the oxygen levels that fish are acclimated. • If a few diseased fish are found, oxygen should be supply into the water. Awaiting solution • Optimum farm management procedure on dissolved oxygen should be established. • Suitable equipment of oxygen supply should be developed. Practical use of oxygen generator