Microbial control in land based aquaculture

Transcription

1 Microbial control in land based aquaculture Kari Attramadal

2 Marine fish larvae Period of rapid growth and development of organs The specific immune system not functional until after metamorphosis Sensitive to infections 2

3 Common (microbial) problems in larviculture? Often large tank to tank variations in survival despite same egg group/feed/physicochemical conditions Antibiotics increase reproducibility of survival The rearing water is an important source of bacteria Microbial control of rearing water! 3

4 Microbial control: Specific pathogens and opportunists Specific pathogens may be stopped by strong hygienic barriers into the system: BIOSECURITY! A lot of the problems in aquaculture caused by naturally occuring opportunistic bacteria that become pathogenic when the host is weakened by environmental stress It is possible to set up selection to outcompete the opportunists!

5 Generally one out of two different strategies favoured: Ecological r/k-theory Max biomass/number of bacteria that can be maintained in the system over time: Carrying capacity (CC) Depends on: Supply of available organic matter Selection Environment Substrate supply per bacteria Favoured ability r-selection Unpredictable/unstable, Empty niches High Rapid reproduction, Fast growth Opportunist K-selection Stable or predictable, crowded Low, Close to CC Competing on limited resources Specialist Colonising bacteria typically r-strategist Succession: bacteria with increasing ability to compete Opportunists gradually replaced by K-strategists 5

6 K-selection: Microbial maturation How? Wait for succession at a given CC Maturing unit = biofilter Low substrate supply per bacteria, favouring the specialists over the opportunists In Organic matter supply Opportunistic bacteria Specialist bacteria Matured water out Time or water flow through system Heterotrophic biofilter

7 K-selection: Microbial maturation Effects on the microbial community composition of the incoming water: A more stable, even and diverse community dominated by slowgrowing specialists Effect on the fish: Significantly higher survival Survival to day 60 ph (end of experiment) Survival to day 32 ph (live feed period) (Vadstein et al., 1993, Skjermo et al., 1997, Salvesen et al., 1999, Attramadal et al., 2012a,b) % Survival FTS 1 FTS 2 FTS 3 MMS 1 MMS 2 MMS 3

8 Incoming water Tank water Selection pressure Intake bacteria Disinfection Intake org.matter Particle removal Water exchange rate Feeding Faeces

9 Perturbances promoting r-selection in intensive aquaculture Organic matter supply Increase in supply of organic matter (carrying capacity) Carrying capacity Number of bacteria Feed Water in tank K selection Barrier against pathogens Disinfection Water in tank K selection r selection Time/flow through the system r selection

10 Closing the gap: K-selection/maturation should be carried out at a carrying capacity (CC) (organic matter supply) similar to that of the rearing tanks Increase CC in the matured inflowing water Reduce CC in the rearing tanks Organic matter CC intake CC intake CC intake CC fish tank CC fish tank CC fish tank 1. Recirculation (RAS) 2. Feed the maturation filter (flow through) 1. High water exchange rates 2. Efficient cleaning 3. Addition of clay instead of algae

11 Closing the gap 1 RAS: incoming water ~ tank water Sign. higher stability of MC of rearing System water! FTS MMS RAS # bacteria in incoming water as % of that in tanks 28 ± 3 19 ± 2 65 ± 4 Bacterial biomass production in incoming water as % of that in tanks 1 ± 0 0 ± 0 29 ± 6 FTS: no maturation, low CC of incoming water compared to the CC of tanks lead to proliferation of bacteria in tank MMS: maturation, but at low CC compared to the CC in the tanks - may open for proliferation in tank RAS: maturation at a CC comparable to that in the tanks lead to stronger buffer agains proliferation of opportunists in the tank K selected CC in ~ CC tank 11

12 Hydraulic retention time In FTS suspended bacteria growing slower than the water exchange rate will be washed out of the tanks: high water exchange rates selects for fast growing suspended bacteria In RAS the total system hydraulic retention time is much higher, dilution is low and keeps even the slow growing suspended bacteria in the system Even if the water exchange rate in tanks are high, the slow growing bacteria may return to the fish tank (as long as they are not disinfected on the way ) I ll be back!! 12

13 RAS 40 % Survival of cod larvae day 30 post hatching RAS 1 0 FTS 1 RAS 2 FTS 2 RAS 3 FTS Coordinate 1 Coordinate RAS FTS MMS Tank water microbial community composition more stable, diverse and even in the RAS Multidimentional analysis of the similarity between bacteria profiles in different water samples

14 Influence on the microbiota of larvae Multi Dimensional Scaling of DGGE-fingerprints of Atlantic cod larval microbiota (day 17 post hatch) Different feed Rotifers fed Rhodomonas Rotifers fed bakers yeast and Marol E Copepods fed Rhodomonas Different water FTS = Flow through system tanks MMS = Microbially matured intake water system RAS =Recirculation aquaculture system (inflowing) (inflowing) (inflowing) w.f L.FTS w.m L.MMS (Bakke et al., 2013) L.RAS w.r Thi My Hanh Truong

15 Closing the gap 2 Feed the maturation filter (flow through system) FED biofilter Fish tanks UNFED biofilter Fish tanks

16 Closing the gap 2 Feed the maturation filter (flow through system) Photo: T. Bardal Increased # bacteria after 3 days of incubation growth potential in the sample No net growth No growth potential: crowded environment resistant to invasion In tanks receiving water from fed biofilter In tanks receiving water from unfed biofilter

17 Closing the gap 2 Feed the maturation filter (flow through system) Microbial community composition Tank water sign. more similar to intake water in FED Replicate tanks sign. more similar in FED Stability in tanks over time, species richness and diversity (Shannon's index H') significantly higher in tanks in FED

18 Closing the gap 2 Feed the maturation filter (flow through system) Microbial community composition of larvae

19 Disinfection UV and ozonation >700 mv most common Efficient on intake water biosecurity! Disinfection of recirculating water is a challenge because of the contents of particles and colour: shaddowing effects/consume of oxidant result in low efficiency: Not really a secure barrier if 5% gets trough and starts proliferating! Ozonation changes the microbial composition (Interdonato, 2012) Regrowth following disinfection changes the microbial composition (Hess-Erga et al., 2010) 19

20 Risk in RAS

21 Action Disinfection before the biofilter Disinfection in the loop at normal production The tank with problems emptied and disinfected Disinfection

22 Disinfection in the RAS treatment circuit Significantly different microbiota in tanks (Attramadal et al. 2012) RAS without disinfection RAS with efficient disinfection Flow through system Multidimentional analysis of the similarity between bacteria profiles in different water samples Total production of fish 30 dph (g) RAS UV 1 RAS UV 2 RAS UV 3 RAS OZ 1 RAS OZ 2 RAS OZ 3 FTS 1 FTS 2 FTS 3

23 Risk Disinfection

24 Action Disinfection Disinfection before tanks Disinfection in the loop at normal production NB!! Problematic because selecting for opportunists!

25 Disinfection in RAS: before rearing tank (John Vegard Øien et al., unpublished) Multidimentional analysis of the similarity between bacteria profiles of different water samples In RAS UV Water treatment only difference RAS tanks RAS UV tanks FTS tanks UV-reactor only difference between RAS and RAS UV The microbial composition significantly different in the three systems In RAS In FTS Microbiota of tanks more similar to that of the incoming water in RAS Microbiota of the rearing water of replicate tanks more similar in RAS

26 Disinfection in RAS: before rearing tank (John Vegard Øien and Elisabeth Kristensen et al., unpublished) Survival of lobster larvae (%) RAS UV RAS UV RAS RAS FTS FTS 80 Survival of lobster larvae (%) Time (days post hatching) Time (days post hatching)

27 Action Physical separation in several independent units No disinfection in the loop at normal operation (simpler, cheaper) Selects against opportunists! The RAS that have problems is emptied and disinfected Unproblematic if contamination in other units than the fish tank

28 Conclusions Similarity of the selective conditions for the microbes in the incoming water and in the rearing water is a key to microbial control in the fish tanks, and opens for optimization of water treatment of the incoming water to benefit larviculture Controlling the microbial carrying capacity in the different components of the system is a very good idea! Using strong disinfection on the incoming water can be smart (biosecurity), but the disinfected water should be microbially matured before it is used for the fish 28

29 Vielen Dank! Recycle! 29