Management of monogenean parasites in sea-cage aquaculture

Transcription

1 Management of monogenean parasites in sea-cage aquaculture Slide Number 1 Presentation overview 1. Examples of monogenean parasite impacts 2. Monogenean lifecycles 3. Parasite management Monitoring Husbandry Treatment 4. Parasite management tool box Slide Number 2 1

2 Presentation overview 1. Examples of monogenean parasite impacts 2. Monogenean lifecycles 3. Parasite management Monitoring Husbandry Treatment 4. Parasite management tool box Slide Number 3 Examples of monogenean parasite impacts A common problem in warm-water sea cage aquaculture Species affected include sea bream, sea bass, barramundi, groupers, puffers, lutjanids, Seriola spp. There are numerous monogenean species with different impacts and host-specificities Economic impact can be severe; e.g. for Seriola spp., up to 20% of production costs Slide Number 4 2

3 Example of Seriola spp. (kingfish, yellowtail and amberjack) Seriola quinqueradiata (Japanese yellowtail, buri, hamachi) Seriola dumerili (amberjack, kanpachi) Seriola lalandi (kingfish, gold-striped jack, hiramasa) Slide Number 5 Example of Seriola spp. cont d Four monogenean species of concern Benedenia seriolae Neobenedenia spp. Herteraxine heterocerca Zeuxapta seriolae Consequences of infection mortality (can be very high if no intervention) poor growth poor FCR higher labour costs higher infrastructure costs Slide Number 6 3

4 Slide Number 7 Benedenia seriolae Skin flukes Neobenedenia spp. HOSTS: all cultured Seriola spp. SITE: body surfaces FEEDS ON: skin and mucous HOSTS: many fish species SITE: fins and body surfaces FEEDS ON: skin and mucous Slide Number 8 4

5 Heteraxine heterocerca Gill flukes Zeuxapta seriolae HOSTS: Seriola quinqueradiata SITE: gills FEEDS ON: blood HOSTS: SITE: FEEDS ON: S. dumerili, S. lalandi gills blood Slide Number 9 Presentation overview 1. Examples of monogenean parasite impacts 2. Monogenean lifecycles 3. Parasite management Monitoring Husbandry Treatment 4. Parasite management tool box Slide Number 10 5

6 Slide Number 11 Presentation overview 1. Examples of monogenean parasite impacts 2. Monogenean lifecycles 3. Parasite management Monitoring Husbandry Treatment 4. Parasite management tool box Slide Number 12 6

7 Parasite management Consider the entire parasite life cycle (eggs, larvae and adults) Focus on limiting the success of the parasite s lifecycle rather than reacting to epizootics Need to define single management units (i.e. sea cages with interacting parasite populations) Slide Number 13 Monitoring Compromise between cost (e.g. labour) and need (i.e. severity and persistence of parasite problems) Best approach is to remove parasites (with praziquantel or freshwater baths) and count them with a microscope Can determine recruitment by counting size classes (indicator of age) Data will allow refinement of parasite management strategies Slide Number 14 7

8 Husbandry methods 1. Fallowing and separation of age classes 2. Orientation of cages 3. Cage environment manipulation 4. Limiting stressors Slide Number 15 Husbandry 1. Fallowing Works when main source of infection is from the caged fish Fallow period may be short - for most monogeneans on Seriola spp days Is the most powerful management option greatly reduce requirement for treatment improved fish health and performance. Slide Number 16 8

9 Husbandry 1. Fallowing cont d Requires minimum of 2 sites, preferably 3 per farm (depending on production cycle) Sites may need to be separated by large distances - Worst case scenario (upper Spencer Gulf in South Australia) > 8km (see Chambers & Ernst 2005; Aquaculture 250: 60 69) Costs and logistical issues need to be considered Slide Number 17 Husbandry 2. Orientation of cages Orientation may influence interaction between cages Infections levels from a source may be lower at points perpendicular to the current than parallel to the current flow (see Chambers & Ernst 2005) Modeling of field data shows that cumulative parasite population growth (i.e. across all cages) is lower with cross current orientation Practical considerations e.g. mooring systems Slide Number 18 9

10 Husbandry 3. Cage environment Sea-cages trap monogenean eggs and probably (?) increase re-infection rates For B. seriolae eggs, the key factor in accumulation was presence of filamentous green algae (Cook 2001, Honours thesis University of Queensland) Antifoulants reduced the accumulation of B. seriolae eggs Net changes would also remove eggs from the environment Slide Number 19 Husbandry 4. Limit stressors Some studies have shown that monogenean populations may grow faster on immuno-suppressed fish However the impacts of stressors on monogenean infections in sea cage aquaculture are not well understood It s likely that immunosuppression affects parasite survival postsettlement Slide Number 20 10

11 Treatment Bath treatment Orally administered treatment Best to apply treatments strategically coordinating in time and space to break lifecycles Slide Number 21 Bath Treatments Bath treatments can have high efficacy Hydrogen peroxide and freshwater commonly used Bathing fish is very costly (labour and infrastructure) Slide Number 22 11

12 Oral Treatment Oral treatment is more efficient - no fish handling, equipment or extra personnel Efficacy generally not as high as bath treatments (fish need to eat a therapeutic dose) Praziquantel and fenbendazole approved in some countries Slide Number 23 Strategic Treatment Apply series of treatments to break the parasite lifecycles; or apply at times when parasite recruitment is low Aim is to suppress entire parasite population not just the adult worms on fish Treat entire management units Requires a good understanding di of parasite lifecycle l parameters to ensure treatment is timed correctly Slide Number 24 12

13 1. Many adult 4. No adult worms worms Many larvae Many eggs No larvae No eggs 2. No adult Juvenile worms worms only 3. Many larvae Many eggs 27 July, Marine Parasitology Copyright 2005 The University of Adelaide Few larvae Few eggs Slide Number 25 Repeat treatment for multiple cages 27 July, Marine Parasitology Copyright 2005 The University of Adelaide Slide Number 26 13

14 Strategic treatment of 26 sea-cages in Australia 17 days 47 days 20 August, Marine Parasitology Copyright 2003 The University of Adelaide Slide Number 27 Problems with strategic treatment Spatial coordination may be difficult Precise timing required Difficult for large farms with many cages Difficult for exposed sites or those with strong tides Effect of strong background infection (eg. wild fish) Very high treatment efficacy may be required Slide Number 28 14

15 Population models: effect of treatment efficacy 27 July, Marine Parasitology Copyright 2005 The University of Adelaide Slide Number 29 Presentation overview 1. Examples of monogenean parasite impacts 2. Monogenean lifecycles 3. Parasite management Monitoring Husbandry Treatment 4. Parasite management tool box Slide Number 30 15

16 Parasite management tool box 1. Monitoring program 2. Husbandry - Fallowing, separation of year classes - Orientation of cages - Net environment antifoulants, net changes - Consider and limit stressors 3. Treatments preferably access to both bath and oral treatments 4. Apply treatments strategically to break parasite lifecycles 5. Minimise sources of infection e.g. escapes Slide Number 31 Thank you Slide Number 32 16