1. General Principles and Aquaculture Systems

2. Aquaculture Production Systems
Definition: Aquaculture Production system may be conveniently divided into three interrelated aspects:
• cultured species
• culture facility
• husbandry.
Note that :
• the species cultured determines the culture facility
• the facility chosen limits the choice of species to be cultured
• species and facility together determine the husbandry practice

3. General Principles General Topics Culture system classification:
Type of structures used
Intensity of culture operations
Water management strategy
Site selection and economics
Hatchery systems
Selection of species for aquaculture
Development of new aquacultural species

4. General Principles Structures Ponds Tanks Raceways Cages Pens
Typically more than one structure will be used during the life span of a cultures species. Structures used in aquaculture include:
Ponds
Tanks
Raceways
Cages
Pens
Substrate

5. General Principles Structures
Ponds: usually earthen impoundments (including natural ponds)
Oldest aquaculture structure
Hole in ground, enclosed waterway, embankment
Used mainly in culture of fishes and crustaceans
Water input and discharge primarily by gravity
Impermeable soils
Soils that support pond ecosystems (this is important feature that determines productivity)

6. General Principles Structures Tanks
Second to ponds as most commonly used structure in aquaculture
Usually above ground on a solid base
Indoors or outdoors
Wide range of sizes
Flow-through or recirculating systems (more later)
Uses include culture of microalgae, macroalgae, various stages of fishes and invertebrates

7. General Principles Structures
Raceways: elongated tanks with canalized flow
Usually continuous water flow from one end to the other
Designed to keep unidirectional water flow along raceway
Suitable for fish such as salmonids that live in shallow streams swimming against current
Need source of good water quality and quantity (most raceways are flow-through)
Potential problem: deterioration of water quality along length
Typically used for high-value fishes

8. General Principles Structures Cages
Original cages: poles or stakes driven into sediment with netting stretched around them (now known as net pens or hapas)
Modern cages are floating structures with net suspended underneath
Square, rectangular or round of variable sizes
Typically used for grow-out phase (months or years)
Require maintenance but not water pumping
Require location with good water quality (protected inshore locations, large freshwater lakes and ponds)
Potential problems: net fouling , predators, diseases and parasites, algal blooms

9. General Principles Structures Pens or hapas
Used in shallow water, typically in ponds
Relatively small
Practiced typically in developing countries (low cost)
Credit: D. Little et al. (FAO)

10. General Principles Structures Substrates – racks, suspended culture
Used to provide attachment surfaces for bottom-dwelling (e.g., bivalves) and attached species (e.g., seaweeds) that are grown in the field for most of their culture

11. General Principles Intensity of culture operations
Definition: The term “intensity” describes the density of cultured organisms per unit volume or unit area. It is meaningful for comparing culture levels for a given species or related species. It is not very useful for comparing culture levels for different groups of organisms. Tilapia at 100 kg/m3 in recirculating systems is considered intensive, whereas shrimp at only 1-2 kg/m3 in ponds is considered intensive.
Energy (cost) considerations: Natural aquatic ecosystems consist of primary producers (primarily plants, including phytoplankton), various levels of consumers (primary or herbivores; secondary or carnivores; tertiary or higher level carnivores), and decomposers. These various trophic levels are arranged into a “food chain.” As a rule of thumb, the amount of energy that can be transferred from one level to the next in the food chain is only 10% (the remaining 90% is “lost” into metabolism, heat generation, waste, reproduction, etc.).

12. Contd..
Implications for aquaculture: The greater the intensity of culture operations, the greater the requirement for energy input into the system. For intensive operations, it is thus much more efficient and cheaper to grow organisms low on the food chain. Approaches differ between developed and developing countries.

13. General Principles Intensity of culture operations Classification
Intensive
Extensive
Semi-intensive

14. General Principles Intensity of culture operations Intensive systems
Requires high energy input (feeds, aeration, water filtration, water pumping, etc.)
No energy recycling (totally non-self-supporting)
All nutrition comes from introduced feeds, with no utilization of natural diets
Simple food chain: feed → cultured organism
Thus, low energy losses/high feed conversion ratios
High rearing densities and production yields (per unit volume or area)
Water quality requirements for target species determines level of stocking (stocking: ponds < cages < raceways/tanks).
Use of ponds, (shrimp), cages (marine fish), raceways (trout), tanks (eels) – but remember that usually different structures are used depending on growth stage of cultured species.
Can be outdoor or indoor

15. General Principles Intensity of culture operations Extensive systems
Relies on natural ecosystem processes for maintenance of water quality and provision of most nutrients
Thus, limited energy input is needed to maintain animal growth and survival
Low stocking densities
Common structures for extensive culture include ponds (“low value” fish – carp, tilapia) and substrate (bivalves, seaweeds)

16. General Principles Intensity of culture operations
Intensive versus extensive systems
Example: Feedlot cattle (intensive) versus free-range cattle (extensive)
Both can be profitable depending on difference between cost of production and value of product

17. Contd…

18. General Principles Intensity of culture operations
Semi-intensive systems
There is no clear line separating intensive from extensive culture
Middle ground = semi-intensive
Semi-intensive culture systems rely to some degree on natural processes and productivity, but there is also supplementation, such as
Aeration
Addition of fertilizers (organic or inorganic)
Addition of feeds (supplemental feeds)
Semi-intensive culture is almost exclusively applied in ponds and allows for increase in stocking density relative to extensive systems

19. General Principles Intensity of culture operations Polyculture
Used in semi-intensive and extensive systems
Refers to the deliberate culture of target and complementary species. Complementary species differ from target species especially in regards to their nutrition so as to minimize competition for resources (e.g., detritivores that “clean up” waste and maintain pond quality)
Polyculture increases production by maximizing utilization of nutritional niches within the pond
A relatively new approach to polyculture: culture of a second complementary species isolated from the main target species. For example, effluent from shrimp ponds (main target species) can be routed through separate ponds for culture of bivalves, plants, microalgae, etc. Second round of culture not only improves the quality of effluent water by removing waste but may also produce additional commercial crops.

20. Contd…
Traditional Chinese polyculture system

21. General Principles Intensity of culture operations
Integrated agri-aquaculture systems (IAASs)
Polyculture is based on the integration of target and complementary aquaculture species in single or separate bodies of water
Integrated agri-aquaculture systems involve traditional agricultural crops (plants, animal) and aquaculture. In these systems plant and animal waste is used to fertilize ponds, but sometimes aquacultural animals (fish and freshwater crustaceans) are grown directly in plant fields (e.g., rice fields)
IAASs are typically applied in the setting of semi-intensive operations, but intensive operations can also be incorporated into an IAAS. For example, when using aquacultural effluent from an intensive pond system for the irrigation of plant crops
Modern aquaculture has moved toward disintegration of aquaculture into monoculture systems, but problems of limited water availability seems to be reversing this trend in some places

22. Contd…
Tierra Mojada Trout Farm, Chihuahua, Mexico

23. General Principles Water exchange/flow systems Classification Static
Open
Semi-closed
Recirculating (closed)

24. General Principles Water exchange/flow systems Static systems
Static system is one in which there is no water replacement during the growth of an organism (except for water added to offset evaporation)
Static pond culture is usually extensive because of difficulties in maintaining water quality
Most global aquaculture occurs in ponds using static systems

25. General Principles Water exchange/flow systems Open systems
The open environment (lake, ocean, etc.). There is no artificial circulation of water through or within the system.
Structures used in this system include cages, racks, etc.
In some cases, such as salmon culture in cages, the open system is intensive (high density of fish with artificial feeds)
In other cases, such as bivalve culture in racks, the open system is extensive (bivalves feed on plankton)
Operation costs of open system is usually low since no pumping is required
Capital costs are high for open intensive systems and low for open extensive systems.
Problems: (1) lack of control over water quality, so site selection is a very important consideration; (2) predation and disease.

26. General Principles Water exchange/flow systems Semi-closed systems
Systems where culture water is confined in discrete units and some degree of water exchange occurs are defined as semi-closed systems. These systems fall between static (no exchange) and open (in the open environment) systems in terms of water exchange.
Ponds, tanks and raceways where significant exchange of water are carried out are considered as semi-closed systems.
Since the farm is not located in the natural environment, there is some control over water quality by regulating the amount exchanged.
In large semi-closed systems with semi-intensive to intensive culture, water flow is generally high (5-10% per day for semi-intensive ponds and 30-40% per day in intensive ponds)

27. General Principles Water exchange/flow systems
Recirculating (closed) systems
Systems are characterized by minimal water exchange, but unlike static systems the water flows internally, usually through waste removal, biofilter, and disinfection units to help maintain water quality.
Costs of construction and operation are high, but yield and product value can also be high and offset costs.

28. Contd….

29. General Principles Hatcheries
So far we have discuss information primarily associated with the grow-out or production aspects of aquaculture (e.g., farming operations)
Hatcheries are those aquaculture facilities associated with reproduction, larval rearing, and supply of juveniles to farms
Considerations for hatcheries (site selection, etc.) are similar as those for nursery and grow-out facilities
General design requirements
Area for holding broodstock
Spawning area
Food production area (plankton, etc.)
Larval rearing area
Early nursery area
Hygiene is major concern. Must be designed to minimize possibility of disease transfer between different areas.
Water quality and feeding regimen are important management considerations

30. General Principles
Selection of species – balance between biology and economics
Biology
Water temperature and quality requirements
Growth rate (fast or slow growing species?): rule of thumb, more than 2 years to market size = not good (rule may be modified according to risks and final value of product)
Feeding habits and cost: 3 phases
Hatchery/nursery
Juvenile
Grow out (usually similar to juvenile in fishes)
Reproductive biology: reliable source of juveniles or “seed” is very important. Wild sources of feed sometime used (table oysters, milkfish in Asia) but availability can be unpredictable and affect aquaculture operations.
Hardiness: adaptability to captive environments is important. Domesticated lines are very useful.

31. General Principles
Selection of species – balance between biology and economics
Economics
Production objectives
Industrial products
Pharmaceutical products
Aquaculture products
Ornamental species
Wild stock enhancement (usually of concern to public agencies)
Marketing: is there a market for the product being considered?
Cost-return analysis (computer software available)

32. General Principles Development of new aquaculture species
If culture techniques are already established for target species, especially if the species is already cultured in the region, the establishment of an aquaculture operation is made easier.
If culture is desired for new species not previously raised in captivity, basic culture techniques need to be developed first.

33. General Principles Development of new aquaculture species
Stages in the development of new culture species
Screening stage
Collection of available information about species – life history, ecology, husbandry. Consider information obtained in relation to the characteristics of proposed aquaculture site.
Legal considerations
Market considerations: local, global demand?
If market does not currently exist, can it be developed?
Economics
Research: biology and husbandry (water quality requirements, optimal stocking densities, reproductive physiology and broodstock management, nutrition and growth)
Pilot trial: semi-commercial validation of aquaculture potential using small culture units and animal numbers
Commercial trial: full-size culture units and larger number of animals; identifies production costs and profits and problems of husbandry of large numbers of animals; preliminary market development
Full-scale production: uses full number of commercial size culture units.

34. General Principles Development of new aquaculture species
Time scale for development – could be well over 10 years
Screening stage: up to 2 years
Research: no less than 5 yeas for species not previously studied
Pilot trial: at least 2 growing generations
Commercial trial: at least 2 growing generations