Farm Intake Water Treatment (FIWT) project FRDC 2017/231 – start July 2018 ‘Water treatment to control influent water biosecurity risk on Australian prawn farms. Effectiveness and impacts on production ponds.’ David Mann Co-invest. Paul Palmer Tom Gallagher Stephen Wesche Bribie Island Research Centre DAF
Project context Enhancing farm biosecurity • Intake water is a significant potential vector • 2018/19 farms in the Logan River Region operating in the white spot control zone Filtration to remove disease vectors is a common biosecurity measure • alone or in combination with a following disinfection step • rotating drum filters – best tech. for high flow volume
Project context “From a biosecurity standpoint, WSSV risk decreases with screen size.” Responsible Aquaculture Foundation / World Bank. 2013. Case Study…Mozambique and Madagascar: Impacts and Management Recommendations. Intake water filtration • Farms now screen pond inflow water • This project is about the next level of protection • requires large farm investment • Need to optimise the cost:benefit • Fine filtration (sub-100µm) as well as water disinfection will impact plankton bloom dynamics • Need to manage adverse impacts
Project results Part 1. Farm monitoring • Performance of commercially operated rotating drum filtration system • Impact of filtration on downstream plankton composition Part 2. Filter mesh size tests • Direct comparison of different filter sizes (20-150µm) Outcomes • What do the results mean for farm biosecurity and operations
Results: Part 1. Farm monitoring Gold Coast Marine Aquaculture Hosted project monitoring activities over the whole 2018/19 production season Operating parameters • two filters in parallel at start, third installed later • nominal 80µm mesh • estimated 5 ML/h flow rate
Results: Part 1. Farm monitoring Farm intake water filtration What it did do… 1. removed large quantities of small crustaceans • in raw water and backwash water - not in filtrate • amphipods, shrimp, crab and other decapod larvae • filter feeders, scavengers, predators • large proportion of these in the 0.3 to 4mm range 2. potentially obstructed entry by Penaeid prawns • very few non- P. monodon prawns within the farm • different from previous years
Small crustaceans in filter backwash
Results: Part 1. Farm monitoring Farm intake water filtration What it didn’t do… 1. Did not greatly affect the copepod population 2. Did not stop glass shrimp ( Acetes sp) from colonising the farm • passage of larval stages? 3. Did not stop barnacles • heavy colonisation occurred within first few weeks Copepods Barnacles on pond liner Glass shrimp
Results: Part 1. Farm monitoring Copepods at different points within the farm • no statistically significant differences • Adult copepods of number / m 3 the four groups present • Some larger adults restricted - Calanoids
Results: Part 1. Farm monitoring Nauplii at different points within the farm • no statistical differences within water supply system number / m 3 • Nauplii not affected by filtration • No difference in body size pre- and post- filter
Results: Part 1. Farm monitoring Plankton much larger than the Acartia sp. copepod 80µm nominal mesh size pass through the filters • copepods over 200µm width • almost all nauplii (to 340µm) Barnacle nauplii HOW? 1. Plankton tend to be bendy, squishy and variably shaped 2. Filter mesh actual pore size and shape
Results: Part 1. Farm monitoring Nominal 80µm mesh – [absolute 125µm] 167µm 167µm ̴166µm ̴250µm Plain weave Weft Warp
Results: Part 2. Mesh size tests Location Bullock Creek Prawn Farm Pumicestone Passage
Results: Part 2. Mesh size tests Mesh size comparison... 1. Tested range (20, 40, 80,150µm), nominal pore size greatly affects copepod population • 20µm retains virtually all copepods and nauplii • 150µm retains around half of copepods and nauplii 2. All copepod groups pass through 40µm & above 3. Copepods and nauplii passing through 40µm are viable 4. Rotifers can pass through 20µm • small species? ; eggs?
Results: Part 2. Mesh size tests Testing set-up • Inshore estuarine water • prawn farm standard • Scaled down drum filter • Reparator Pty. Ltd (manuf. by Adriyatic) • Stainless woven mesh • 20, 40, 80, 150µm, (raw) • 80µm same weave as GCMA • 21 tank array • plankton mesocosms to assess animal viability
Results: Part 2. Mesh size tests Copepod density post-filter Initial Day 14 # / m 3 # / m 3 • Comparatively large restriction step from 150 to 80 µm • Copepod size did not follow same pattern as abundance
Results: Part 2. Mesh size tests All nauplii density post-filter Initial Day 14 # / m 3 # / m 3 • 150µm mesh restricts ̴50% of nauplii, 40µm ̴25% • Average body size of filtrate nauplii same for all mesh sizes
Outcomes 1. Logan River plankton and glass shrimp samples WSSV negative (intake and in farm; over the season). 2. Drum filtration at nominal 80µm effectively excludes higher WSSV risk organisms at practical flow rates. 3. Nominal 80µm stainless filter has a low impact on pond bloom. • time to peak copepod density delayed but main groups present to form normal productive pond bloom 4. To prohibit barnacle entry need 40µm or less filter mesh. • larval stages of crustaceans still enter (lower risk?) 5. Nominal 40µm stainless filter would allow some copepod entry but retard pond population development. 6. Filtration alone lowers probability of vector intrusion. • chemical disinfection – high protection
What next… This project • sampling completed • final report will have more detailed analyses
What next… Future work on water biosecurity… 1. Continue farm monitoring and testing • performance and impacts of the re-developed systems being implemented on farms this season – ‘Growing together’ theme – sharing information 2. Optimise chemical disinfection for high water biosecurity • options – oxidants, eg ozone, other oxidants; trichlorfon • conditioning of disinfected water important 3. Creating healthy pond systems • water/pond biome management • adapting overseas innovations to the Australian context
Acknowledgements • FRDC and DAF funded the project • Gold Coast Marine Aquaculture opened their Logan River farm to regular sampling and assisted on farm activities • Frank Coman and Julian Uribe Palomino (CSIRO) assisted pond sampling method development and conducted training of DAF staff in zooplankton identification • Bullock Creek Prawn Farm allowed use of hatchery and intake facility and assisted in systems set-up • Reparator Pty. Ltd supplied the fully equipped drum filter and different size mesh screen replacements for tests
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