What exactly is Aquaculture?
‘Aquaculture’ is a rather self-explanatory word — it refers to the culturing of aquatic species. Some believe that aquaculture is the solution to global wild fish decline, while others believe aquaculture exacerbates wild fish conservation. Are there preferred types of aquaculture? And why is aquaculture so controversial?
Aquaculture involves the rearing, breeding and harvesting of aquatic species for different purposes. This might include food consumption, restoration of threatened species and ornamental uses.
Aquaculture is essential for global food security. Currently, 52% of the fish we consume are derived from aquaculture. Asia is by far the biggest producer of farmed aquatic species, in 2018, 73 million tonnes of fish aimed for consumption was reared in Asia, which amounts to 89% of the world’s total.
Many countries have turned to aquaculture to prevent overfishing. Aquaculture is also more efficient than land agriculture, since it mostly depends on existing water environments (ponds, lakes, oceans) for farming, reducing the need to clear land. Further, specific forms of aquaculture such as Bivalve and Seaweed Farming can sequester carbon and clean up waterways. Due to these factors, the Food and Agriculture Organisation (FAO) claims that aquaculture is “probably one of the fastest growing food-producing sectors.”
How is aquaculture practiced?
You may conjure the visual of fish in sectioned nets when you hear the word ‘aquaculture’, but caged systems are only one of the many types of aquaculture being practiced.
Aquaculture is practiced in three main environments, namely Freshwater, Brackish Water and Seawater.
Freshwater Aquaculture occurs in lakes or ponds and is usually carried out in fish ponds, fish pens or fish cages. Species commonly raised in freshwater include Tilapia, Catfish and the Giant Freshwater Prawn.
Brack Water is water that is less saline than the ocean, but more saline than freshwater. Water bodies close to the coast usually contain brackish water — this includes estuaries, mangrove swamps and certain ponds or lakes. Milkfish and Mullet are two common fish species reared in brack water.
‘Marine Aquaculture’ occurs in oceans, mainly in coastal areas or on man-made rafts. Fish cages or sectioned nets are used for seawater fish farming, while substrates* are used in the case of Bivalve or Seaweed farming. Popular fish species farmed in seawater include Sea Bass, Grouper and Yellowtail.
[*Substrates: In Biology, a substrate is the base on which an organism lives. Examples of substrates include mud, sand and cobble]
Fun Fact: How is Salmon farmed?
As an anadromous fish**, Salmon are born in freshwater, mature at sea, then return to freshwater streams during spawning season. Fish farms take different approaches when rearing salmon, with some farms raising them entirely in freshwater or seawater, while others move the species from freshwater to seawater as they mature.
[**Anadromous fish: Fish species which divide their lives between fresh and seawater. Anadromous fish are born in freshwater, spend most of their lives in seawater, then return to fresh water during spawning season.]
What are the main types of aquaculture?
Many varieties of aquaculture are practiced; some aquaculture farmers choose to take an ‘integrated aquaculture’ approach to mimic natural systems.
Bivalves are aquatic molluscs with a hinged shell. Oysters, Mussels and Scallops are all examples of Bivalves. Due to its ecological benefits, Bivalve farming has captured the attention of researchers and entrepreneurs alike.
Bivalves have significant eutrophication potential. Eutrophication occurs when fertilisers are washed into waterways, causing algae blooms. Since Bivalves consume excess algae, they help to clean up waterways and oceans plagued by eutrophication, playing an important part in water clarification.
Bivalves’ low maintenance is another advantage; as they ‘consume’ organisms such as algae and other chemical compounds in the water, they do not require additional feed. Bivalves are therefore highlighted by food institutions such as Cambridge Global Food Security as a more sustainable, low-impact protein source compared to animal meat. Relative to the 340 tonnes of Greenhouse Gas (GHG) per tonne of edible beef, Bivalves only emit 11 tonnes of emissions per tonne of Bivalve protein.
Finally, they are also a nutrient-dense protein source, high in Omega-threes, protein and key minerals.
Bivalves such as Clams or Oysters are grown directly on the beach, in protective netting or in bags buried under the sediment. Other methods of Bivalve farming involves rearing them on long underwater lines suspended from rafts — this is a method that is commonly used for farming Mussels.
Seaweed Farming is another type of aquaculture that has garnered significant attention because of its environmental benefits. Not only does Seaweed have impressive carbon sequestration abilities, it also releases Oxygen and can help to deacidify the oceans. Seaweeds are estimated to sequester 200 million tonnes of Co2 every year (an amount that equals the total emissions of the state of New York).
Seaweed is grown via a method called vertical or 3D Farming, where they are harvested on long lines suspended 4–8 feet below the water surface.
Fish farming refers to the breeding of fish for the purpose of consumption. There are many types of fish farming, three of the most common methods include: open pen systems, raceways and recirculating aquaculture systems.
Open Pen or Caged Systems
Fish are cultured in large mesh cages or sectioned off in nets in freshwater or seawater. This system has raised significant environmental and hygiene concerns. One of the biggest concern is the spread of disease and parasites to wild populations. Another concern is the risk of ‘escaped fish’ interbreeding with wild populations, thereby causing species decline.
Raceways or Flow-Through Systems
Raceways are artificial rectangular channels with an inlet for natural water sources and an outlet for wastewater. Raceways are common in areas where electricity is scarce, but a reliable source of water is available. Freshwater species are often cultured in raceways.
Recirculating Aquaculture Systems (RAS)
RAS systems are touted as one of the most environmental forms of fish farming. It involves closed chambers where electricity is used to filter culture water through a treatment pump, such that the water can be used continuously
The main benefits of RAS systems include water conservation and hygiene. However, RAS systems have high operating costs and also increase emissions due to its electricity consumption.
Integrated Multi Trophic Aquaculture (IMTA)
Also known as ‘Polyculture’ or ‘Integrated Aquaculture’, IMTA is a flexible system that can be adapted to open-water, land-based or tropical farming systems.
Based on natural ecological principles, IMTA leverages the synergy between aquatic species to create a self-sustaining system where each species plays a provisionary or regulating role.
For example, farmers cultivate fed fish such as Fin Fish or Shrimp with extractive species such as molluscs, which recycle fish waste and clean the water by processing waste into nutrients. In China, Puffer Fish is farmed with Shrimp. The system designed to prevent outbreaks of diseases, where Puffer Fish play a ‘regulating role’ by preying on weak shrimp, thus eradicating disease outbreaks.
With 2022 being hailed as the year of ‘Ocean Conservation’, many institutions are looking to aquaculture to relieve wild fish stocks and to stabilise ocean environments. Despite this, aquaculture farming is also wrought with controversies. Read more about aquaculture’s controversies this article.
This article will be followed by an additional part covering the key benefits, detriments and controversies in Aquaculture.