Comprehensive Notes on Aquaculture Methods and Practices

Overview of Aquaculture Environments and Practices

Aquaculture reflects a wide variety of practices across three primary environments: freshwater, brackish water, and marine systems. These practices vary significantly depending on the culture organisms. Freshwater aquaculture is primarily conducted in fishponds, fish pens, fish cages, and occasionally in rice paddies. Brackish water aquaculture is centered around coastal fishponds. Marine culture, also known as mariculture, utilizes cages or substrates such as stakes, ropes, and rafts for farming mollusks and seaweed. The core practices involve mariculture, metahaline culture, brackish water culture, and freshwater culture.

Mariculture Techniques and Systems

Mariculture involves the culture of fish, prawns, and lobsters utilizing floating cages. For bivalves like mussels and pearl oysters, specialized methods such as racks, rafts, ropes, poles, and long lines are employed. Seaweed is typically farmed using nets or webbings. Cage culture is defined as an aquaculture production system featuring a floating frame, net materials, and a mooring system consisting of ropes, buoys, and anchors. These nets, which can be round or square, hold large populations of fish and are installed in reservoirs, rivers, lakes, or the sea. There are four distinct types of fish-rearing cages: fixed cages, floating cages, submerged cages, and moveable cages.

Raft culture serves as a commercially important method for intensive aquaculture, consisting of rectangular wooden frames, often made of bamboo, that float on the water using empty drums. The basic unit includes a long floating rope buoyed by numerous floats and anchored to the bottom. Rack culture is an advanced intertidal method where steel racks are placed in the sand or mud. Plastic mesh bags containing small culture organisms are laid on top of these racks, allowing the tides to surround them with water. Pole culture, also known as "Bouchot" or stake culture, is common in France. It uses oak tree branches or trunks between $4-6\,m$ in length, staked in rows approximately $0.7\,m$ apart in the soft mud of the intertidal zone during low tide.

Long-line culture provides an alternative to raft culture in areas prone to heavier wave action, using a cable or chain supported by floats and anchored at both ends. Bottom culture follows the traditional method of placing oysters or oyster shells directly on the bottom of a lease to catch wild stock. Lastly, artificial reefs are benthic structures made of natural or man-made materials designed to protect, restore, or enhance marine ecosystems.

Metahaline and Saltwater Pond Culture

Metahaline culture takes advantage of the off-season of salt manufacture by utilizing salt pans for fish culture. Specifically, the culture of brine shrimp, known as Artemia Salina, is performed in super-saline salt pans where salinity levels exceed $200\%$. The nauplii of Artemia are a protein-rich live food for finfish and shellfish. Furthermore, the dormant eggs or cysts produced under unfavorable conditions can be a valuable export. Saltwater ponds, also called marine ponds, are filled with sea water and contain similar species as the ocean. Salt marshes found at the edges of these ponds are home to coastal plants adapted to occasional seawater flooding.

Brackish Water and Tidal Pond Culture

Brackish water environments are rich in oxygen and plankton. Organisms in these areas, such as the mangrove crab (Scylla serrata), can be cultured in tidal ponds, pens, cages, or through rack, raft, and rope systems. Tidal ponds are shallow coastal inlets that fill and empty according to the tide, often associated with marshes and tidal flats. Pen culture involves raising fish in a volume of water enclosed on all sides except the bottom, which is formed by the natural lake or sea floor. This system allows for the free circulation of water and is considered a hybrid between pond and cage culture.

Freshwater Culture Methods

Freshwater culture focuses on raising and breeding aquatic animals like fish, shrimp, crabs, and shellfish, as well as aquatic plants, for economic purposes in inland waterways. Composite fish culture is a specialized system where five or six different fish species are grown together in one pond. Species are selected based on different feeding habits to ensure they do not compete for food, maximizing the utilization of pond resources. Air-breathing fish culture is used in shallow, low-oxygen waters for species like Channa, Clarias, and Heteropneustes. Predator-prey culture (such as murrel-tilapia) is another shallow-water practice where predators are farmed alongside their prey. Monosex culture involves producing either all-male or all-female populations, while monospecies culture focuses on a single individual fish species.

Open Water Systems: Mollusks and Seaweed

Sea farming is often low-cost and labor-intensive, making it ideal for coastal communities where municipal fisheries have declined. Mollusk culture, particularly bivalves, is highly productive in Asia and the Pacific. In $1984$, mollusks represented approximately $35\%$ of coastal aquaculture production by gross weight. Major species include oysters (Crassostrea spp.), mussels (Perna spp.), clams, cockles, and scallops.

Seaweed farming provides food and industrial colloids like agar and carrageenan. Eucheuma, a red algae, is a primary source of carrageenan. Caulerpa lentillifera, a green alga, is a nutritious salad dish containing calcium, potassium, magnesium, sodium, copper, iron, and zinc; it also serves as an anti-fungal agent and helps lower blood pressure. Gracilaria is cultivated in Taiwan for its agar extracts.

Fishpond, Cage, and Pen Technical Details

Fishpond culture is the earliest aquaculture form, dating to the Yin Dynasty ($1400-1137\,B.C.$). Standard ponds use stagnant water, but running water ponds are used in highlands. Cage culture originated in Kampuchea approximately $200\,\text{years}$ ago and was initially used for transporting live fish to markets. While the terms "cage" and "pen" are sometimes used interchangeably in North America, they are distinct: a cage is fully enclosed by mesh, while a pen uses the natural bottom of the water body as its floor.

Site Selection and Species Classification

Success in aquaculture begins with proper site selection, which dictates the project's design and management. Key factors include soil quality, land elevation, tidal characteristics, vegetation, water supply, water quality, accessibility, and the availability of manpower.

Species are categorized by environment:

• Freshwater: Carps, tilapia, catfish, snakehead, eel, trout, goldfish, gourami, pike, tench, salmonids, palaemonids, and the giant freshwater prawn Macrobrachium.
• Brackish Water: Milkfish (Chanos chanos), mullet (Mugil sp.), and various penaeid shrimps (Penaeus monodon, P. orientalis, P. merguiensis, P. penicillatus, P. semisulcatus, P. japonicus, and M. ensis).
• Marine: Sea bass, grouper, red sea bream, yellowtail, rabbitfish, and marine shrimps.

Questions & Discussion

1. Question: What is an aquaculture production system made of a floating frame, net materials, and mooring system? Answer: Cage culture.

2. Question: These are rectangular wooden frames floating on the water used for intensive aquaculture. Answer: Raft culture.

3. Question: What refers to small enclosures used for confinement or safe keeping of domestic animals? Answer: Pen culture.

4. Question: The culture of fish in meshed boxes placed in water is called? Answer: Cage culture.

5. Question: Fixed cages are installed in what kind of water? Answer: Running water.

6. Question: What is an enclosure system used to partition areas of an open aquatic body? Answer: Barriers (Nylon-Net barrier).

7. Question: What culture refers to the culture of either all male or all female populations? Answer: Monosex.

8. Question: Raising and breeding aquatic animals like fish, shrimp, and shellfish in reservoirs or lakes is called? Answer: Freshwater culture.

9. Question: What is a shallow coastal inlet that fills and empties as the tide rises and falls? Answer: Tidal ponds.

10. Question: What kind of saltwater ponds can be called marine ponds? Answer: Stagnant saltwater ponds.