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FMA2001 L12 Molluscs.pptx

  1. Principles of Aquaculture FMA2001 (2+1) LU 12: Molluscs culture
  2. Learning Outcomes 1.Preparation and management of mussels, cockles and oyster culturing
  3. Introduction • Molluscs are important phylum of invertebrate animals • They are mostly marine and near shallow waters • Major class: • Cephalopod  Squid, octopus, cuttlefish • Gastropods  snails, slugs, abalone • Bivalves  oyster, cockles, mussels
  4. Mussel • shells are solid, inequilateral • External shell consist of two shells/ valves • Normally cultured species: • Perna viridis (green mussel) • Mytilus edulis (blue mussel) • Modiolus metcalfei (brown mussel)
  5. • Found at the littoral zone / intertidal zone--> brackish to marine species. • Filter-feeder  plankton and detritus • Very short food chain (one link only) • Fast growth rate • Reach sexual maturity within 1 year and spawn with rising seawater temperature. • Two phase in life cycle planktonic or larval stage (2 weeks) & sessile adult stage.
  6. Measurement
  7. Preparation for culture Site selection: • well protected/ sheltered bay protect from wind and waves • Presence of natural mussel spatfall • Not recommended: areas as catchment for excessive flood waters. Water level, salinity and temperature not consistent.
  8. Preparation for culture Water quality • Rich in plankton (greenish colour); not too rich (harmful algal bloom) • Free from pollution (avoid industrial or domestic area) • Water depth 2 m • Temperature 27-30 °C • Salinity 27-35 ppt
  9. Natural seed collection • Seed depends on natural spat. • collect using polyethylene and palm-coconut fibre ropes. • Using ropes on rafts to collect seeds during peak spawning period. Can be collected at natural mussel bed during low tide. • Spat settled on ropes and grow to 30-40 mm • Transplant to fresh ropes to avoid crowding. • Rope 10m length and 70cm apart from other ropes. • 18-24 months to harvest
  10. Hatchery • produce consistent seed supply at an acceptable cost. • can produce polyploids, hybrids and selected strains. • hatchery use algal food and temperature shock for inducing spawning. • after spawning, larvae are fed ad libitum and allowed to grow until they are ready to set onto ropes (2 weeks) • mussels of 1 mm size are transferred to nursery to grow until they reach 10 mm size • then move outdoors into grow out system
  11. Culture method Mainly three types of culture method • Bottom culture (at the natural intertidal zone. Firm bottom) • Off bottom culture (at Inter-tidal and shallow water) • Deep water culture
  12. Intertidal and shallow water culture 1. Rack or tray culture: mussels cultured off bottom. At low tidal range areas. using bamboo or metal trays.
  13. Intertidal and shallow water culture 2. Hanging method: using ropes or strings for mussel to attach. 3. stake method: between rack and hanging. Using bamboo poles.
  14. Deep water culture Long line or raft
  15. Harvest • marketable size (about 40 mm, which takes 2 years) • Harvest should cause least stress to the mussels • Pulling or scrap the mussel  loss of moisture after harvest and physical damage early death. • Cut the byssal thread and leave it intact to the body • Exposure to the sun, bagging and transport also increase stress of mussels.
  16. Depurification • Mussels are filter feeders • Stomach filled with mud, sand, bacteria. • Keep in clean, sterilized and filtered seawater for 2 days to 2 weeks depending on harvesting location. • Ozone used for sterilization of water powerful oxidizing agent to kill bacteria and virus.
  17. Disease and control Disease Agent Type Syndrome Measures Parasitic infection Marteilia maurini Protozoan Potentially lethal; haemocyte infiltration of digestive gland (connective tissue and epithelia); extensive destruction of the digestive gland in heavy infections No curative measure; prevention & site selection; monitoring mussel transfer Viral disease Picornaviridae-like virus Virus Heavy mortalities No curative measure; prevention & site selection; monitoring mussel transfer Vibriosis Vibrios Bacteria Not specified No curative measure; prevention & site selection; monitoring mussel transfer Rickettsiosis Rickettsia-like organisms; Chlamydia- like organisms Bacteria Microcolonies in the epithelial cells of the gills and digestive gland No curative measure; prevention & site selection Red 'worm' diseases Mytilicola intestinalis; Mytilicola orientalis Copepods Usually commensal but may retard growth No curative measure; decrease stocking density
  18. Disease and control Disease Agent Type Syndrome Measures Various parasitic infections Steinhausia mytilovum Micro-sporidian Infects cytoplasm of mature mussel ova; incites a strong haemocyte infiltration response No curative measure; prevention & site selection; monitoring mussel transfer Cliona Sponge Penetrates the periostracum forming holes in the outer surface and a tunnel network throughout the shell None Prosorhynchus sp Bucephalid trematode Mantles show abnormal colouration (patchy yellow-white) in heavily infected individuals; castration; weakness; gaping None Prosorhynchus sp Bucephalid trematode Mantles show abnormal colouration (patchy yellow-white) in heavily infected individuals; castration; weakness; gaping None Pea crab parasites Pinnotheres pisum Crustacean Reduces market value No curative measure; decrease stocking density
  19. Oyster
  20. Biological features • Shell solid, extremely rough, irregular shape, interior of shell is white. • habitat: estuarine species. attached to rocks. can be found on mud or sandy bottom. • salinity tolerance 20-35 PSU • marketable size around 30 months
  21. Crassostrea belcheri Crassostrea rivularis Saccostrea cucullata Ostrea folium
  22. Seed supply • normally from natural spat. Hatchery • Broodstock from commercial growout facility--> maintained at best possible condition • group of adults are collected during natural spawning season. • cultured in algae supplemented seawater. after 6 weeks in hatchery condition, induce spawning by thermal shock • larvae are grown in hatchery for 2-3 weeks using phytoplankton (Isochrysis galbana or Pavlova lutherii, Chaetoceros calcitrans or Thalassiosira pseudonana, Tetraselmis sp)
  23. Nursery • supplied with algae-rich water • density can be 100kg/m3 • from 1 mm to 15 mm then transferred to grow-out • Yields of 10- 15mm seeds for grow-out can reach 3 tonnes/ ha
  24. Grow-out • Entirely sea-based • Method: bottom, off-bottom, suspended culture method (depending on environment) • Growth best at 25°C & 30 PSU. • Depends greatly on natural phytoplankton availability • Takes around 2 years to reach market size (with shell 100g) • Extensive system with mixed growing phase will yield around 25 tonnes/ha/year • Separated growth phase farm can yield up to 70 tonnes/ha/year
  25. Bottom culture • Seed of 1-2g sown on intertidal zone at 400/m2 protected with net or fence from predators OR • 200/m2 unprotected  will require no further husbandry until the oyster reach marketable size.
  26. Suspended culture • Long lines & rafts • Attached to strings, wires, ropes, nets, mesh bags, plastic trays and suspended in the water vertically. • Normally used in deeper waters. • Need to check for fouling often, lines may sink due to fouling organisms
  27. Floating culture • Wooden/ plastic frame trays with mesh bases with floats
  28. Harvesting • Harvested at 100 g or shell length >75mm • Bottom culture: hand raking, picking, dredging. • Off-bottom culture: using small boats, detach using mechanical washing and grading machinery. • Beware of harvesting during harmful algal blooms (paralytic shellfish poisoning, diarrheic shellfish poisoning)
  29. Cockles
  30. Site selection • Shallow bay, sheltered from strong wind and strong wave action • Substrate: 6-10 inches depth mud flat with clay or silty clay substrate and mangrove forest cover • Water depth range around 1-2 meter (highest tide and lowest tide) • Land elevation: gradient of 5-15 degree. If gradient too small, culture area will be exposed during low tide and gradient too big cockles don’t grow well. • Water movement: slow water current 0.1 m/sec • Salinity: from 23 -30 PSU
  31. Seed preparation • Collect 1-2 mm size spat from the wild using baskets or mesh to filter the mud away • Collect using wooden mud sled on shallow-drift boat
  32. Culture techniques • Stocking density: for spat of 5000pcs/ kg 2000 pcs/m2 • As cockles grow, population will be thinned down • Larger cockles will be removed and resown at 300 pcs/m2 • After 4 months cockles should reach 480pcs/kg • Harvesting around 18 months after seeding or 50pcs/kg (4cm)
  33. Challenges and issues 1. Seed shortages – over harvest of spat from the wild 2. Predation - birds 3. Water quality – pollution from industrial waste 4. Biotoxins – harmful algal bloom – Paralytic shellfish poisoning & diarrhetic shellfish poisoning