larvi 2013 Kari Attramadal 6th fish & shellfish larviculture symposium ghent university, belgium, 2-5 september 2013

Transcription

1 larvi th fish & shellfish larviculture symposium Control of the selective pressure on microbes in rearing tanks through manipulation of the incoming water increases survival of marine fish larvae Kari Attramadal ghent university, belgium, 2-5 september 2013

2 2 Control of the selective pressure on microbes of the incoming water increases survival of marine fish larvae Attramadal, K. a, Øie, G. b, Kjørsvik, E. a, Minniti, G. a, Skjermo, J. b, Bakke, I. c, Østensen, M-A. b, Olsen, Y. a, Vadstein, O. c a Department of Biology, NTNU, 7491 Trondheim, Norway b SINTEF Fisheries and Aquaculture, Department of Marine Resources Technology, 7465 Trondheim, Norway c Department of Biotechnology, NTNU, 7491 Trondheim, Norway

3 3 Marine fish larvae Period of rapid growth and development of organs The specific immune system not fully functional until after metamorphosis Sensitive to infections

4 4 Common (microbial) problems in larviculture? Often large tank to tank variations in survival despite same egg group, feed and physicochemical conditions Antibiotics increase reproducibility of survival The rearing water is an important source of bacteria for the larvae Microbial control of rearing water!

5 5 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!

6 6 Generally one out of two different strategies favoured: Ecological r/k-theory Carrying capacity (CC) = Max biomass/number of bacteria that can be maintained in the system over time 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

7 7 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

8 8 K-selection: Microbial maturation Effects on the microbial community composition of the incoming water: A more stable, even and diverse community dominated by slow-growing specialists Effect on the fish: Significantly higher survival Survival to day 60 ph (end of experiment) Survival to day 32 ph (live feed period) % Survival FTS 1 FTS 2 FTS 3 MMS 1 MMS 2 MMS 3

9 9 Incoming water Tank water Selection pressure Intake bacteria Disinfection Intake org.matter Particle removal Water exchange rate Feeding Faeces

10 10 Perturbances promoting r-selection in intensive aquaculture Organic matter supply Increase in supply of organic matter (carrying capacity) Carrying capacity Number of bacteria Feed K-selection Barrier against pathogens Disinfection K-selection r-selection Time/flow through the system r-selection

11 11 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

12 12 Closing the gap - gaining control K-selection/maturation of the microbial community of incoming water at a carrying capacity (CC) similar to that in the tanks 1. RAS 2. Feed the maturing unit (flow through) Reduce the use of disinfection inside the RAS 1. In the recycling loop 2. Before tanks

13 13 Closing the gap 1 Stability of microbial community composition RAS: incoming(moving water window ~ analysis) tank water 1.0 System water! FTS MMS RAS # bacteria in incoming water as % of that a in tanks 28 ± 3 19 ± 2 65 ± 4 Bacterial biomass production in incoming water a as % of that in tanks 1 ± 0 0 ± 0 29 ± Bray-Curtis similarity FTS: no maturation, 0.6 low CC of incoming water b compared to the CC of tanks lead to proliferation of bacteria in tank b 0.4 MMS: maturation, but at low CC compared to the CC in the tanks - may open for proliferation in tank 0.2 a RAS: maturation 0.0 at a CC comparable to that in the tanks lead to stronger buffer agains proliferation of opportunists in the tank FTS in MMS in RAS in K-selected FTS tanks MMS tanks Sign. higher stability of MC of rearing a RAS tanks CC in ~ CC tank

14 14 RAS 40 % Survival of cod larvae day 30 post hatching Coordinate RAS 1 FTS 1 RAS 2 FTS 2 RAS 3 FTS RAS FTS MMS Tank water microbial community composition more stable, diverse and even in the RAS Coordinate 1

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

16 16 Closing the gap 2 Feed the maturation filter (flow through) Microbial growth potential in tank water (3 days) 300 Growth in sample after 3 days incubation (%) No net growth Photo: T. Bardal Increased # bacteria after 3 days of incubation growth potential in the sample No growth potential: crowded environment resistant to invasion Time (days post hatch) In rearing tanks receiving water from fed biofilter In rearing tanks receiving water from unfed biofilter

17 17 Closing the gap 2 Feed the maturation filter (flow through) 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, diversity (Shannon's index H') and evenness (J') significantly higher in tanks in FED Larval performance Survival (27 dph): 5% in FED, 20% in UNFED Stress tolerance: significantly higher in FED Growth: significantly higher in FED* FED biofilter system UNFED biofilter system Photo: T. Bardal DGGE

18 18 Reduce the use of disinfection inside the RAS 1 In the recirculation loop Strong disinfection within the RAS loop may reduce the maturing effect of the microbial community: FTS: high disinfection efficiency on the incoming water lead to to proliferation of bacteria in tank RAS UV: high disinfection efficiency reduce abundance and activity of bacteria in incoming water and may open for proliferation in tank RAS O 3 : ozonation to 350 mv in protein skimmer results in low or no disinfection and an incoming water similar to the water in tanks

19 19 Reduce the use of disinfection inside the RAS 1 In the recirculation loop RAS O3 more mature and stable microbial community than RAS UV Incoming water microbial community composition more similar to tank water in RAS O3 compared to RAS UV and FTS: (a) Total bacteria cell counts ml -1 RAS UV RAS O 3 FTS RAS UV reservoir RAS O 3 reservoir FTS reservoir Time (days post hatching) Microbial activity (production of bacterial biomass) in tanks compared to inflowing water: O 3 RAS UV RAS FTS Total production of fish 30 dph (g) RAS UV 1 RAS UV higher 3.0 higher 17.5 higher RAS UV 3 RAS OZ 1 RAS OZ 2 RAS OZ 3 FTS 1 FTS 2 FTS 3

20 20 Reduce the use of disinfection inside the RAS 2 Before rearing tanks (From John Vegard Øien) Survival of lobster 14 dph 60 % survival Best survival in RAS with no disinfection Microbiota yet to be analysed 10 0 RAS 1 RAS 2 RAS UV 1 RAS UV 2 FTS 1 FTS 2

21 21 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 avoid it in the recirculation loop!

22 22 Recycle! Thank you for listening! Kari Attramadal