This document provides information on mollusc culture, including mussels, oysters, and cockles. It discusses the biological features and life cycles of these molluscs and outlines best practices for their cultivation, including site selection, seed collection and preparation, nursery and grow-out methods, harvesting, and issues to consider. The key steps involve natural seed collection or hatchery production, nursery culture, transfer to intertidal or subtidal grow-out using various suspension or bottom methods, and harvesting at market size, typically after 18-24 months. Disease prevention and control are also important considerations.

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

16. 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.

17. 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.

18. 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

19. 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

20. Oyster

21. 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

23. Crassostrea
belcheri
Crassostrea
rivularis
Saccostrea
cucullata
Ostrea folium

25. 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)

26. 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

27. 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

28. 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.

29. 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

30. Floating culture
• Wooden/ plastic frame
trays with mesh bases
with floats

31. 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)

32. Cockles

33. 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

34. 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

35. 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)

36. 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