21 Aquaculture
Patricia Corbett and Nikita Dubberley
Aquaculture is one of the fastest growing food sectors globally and contributes almost 50% of overall fish production (Md Noor and Harun, 2022; Verdegem et al., 2023). Aquaculture has been suggested as a possible alternative for fisheries towards mitigating food security problems and preventing the loss of wild fish supplies. This industry has increased tremendously over recent decades, with less than 19 million tonnes in 1950 to 122 million tonnes in 2020 (FAO, 2022). Although fish farming is often referred to a sustainable activity, it has been associated with a number of potential ecological consequences. These include eutrophication of aquatic ecosystems, intensive use of land and water, ecotoxicity of ecological systems through the use of chemicals, and invasion of non-native species (Peay et al., 2019). Hence, it is of the essential to evaluate present aquaculture methods and find the most environmentally acceptable aquaculture production systems that can help ensure global food security.
Text Attribution
This text is from “Towards Sustainable Aquaculture: A Brief Look into Management Issues” by Noorashikin Md Noor & Siti Norliyana Harun, which is licensed under CC BY 4.0, except for the introductory sentence, which has been added by Trish Corbett.
End Text Attribution
‘Underwater Photography of School of Fish’ by Harrison Haines used under a Pexels License
Most Common Marine Aquaculture (Mariculture) Systems
Open the sections below to learn about the most common mariculture systems.
Open aquaculture systems
Open aquaculture systems are where culture organisms are in the ocean. They may be in cages, on sticks, ropes, or racks. There are active or passive feeding systems.
Active feeding systems are those such as salmon cages where the fish are actively fed their diet, often in pelletised form specifically designed for optimal growth, nutritional benefits and taste of the species.
Passive feeding systems are those such as algal culture and filter feeding organisms like mussels that are not actively fed. They passively feed or gain their nutrition from the water column.
Often recirculating aquaculture systems or flow through systems are used in combination with cage culture systems as juveniles are hatched out and reared to a certain point before being taken to open cage systems.
If you are interested in learning more about cage culture, watch The Future of Seafood from ChangingSeasTV.
Recirculating Aquaculture Systems
Recirculating Aquaculture Systems are land-based aquaculture facilities. As the name suggests, they recycle the water in the system rather than continually getting it from an external source. The water is treated by a range of biological and mechanical treatments to ensure good water quality (VFA, 2023).
Watch the video below to explore Recirculating Aquaculture Systems further.
Flow through aquaculture systems
Flow through aquaculture systems are often used for culture of organisms such as abalone. These systems can include raceways, ponds and / or ponds. The water is taken, for example, from the ocean, run through the system and then passed back into the ocean with little or no treatment (VFA, 2023).
Impacts of Aquaculture
Aquaculture has many benefits, however while there is far greater efficiency and working to significantly reduce impact in advanced systems, there has traditionally been a number of impacts including increased nutrients causing eutrophication, escape, and habitat destruction.
Expand the section below to learn more.
Further impacts of Aquaculture
Further impacts of Aquaculture
Aquaculture utilises water as a culturing medium, hence, the survival of aquaculture organisms is dependent on the water quality—for example carbon dioxide (CO2), ammonia (NH3), pH, and dissolved oxygen (DO) (Noor & Das, 2019). Aquaculture activities have an impact on water quality due to the feed waste and excretion from the cultured organisms, which eventually affects the organisms being cultured. Different culture systems affect the environment in different ways because of the differing management practices and waste (faeces, indigestible solids, uneaten feed) (Noor & Das, 2019). Common practices include the release of materials—such as dissolved nutrients, uneaten food, faeces, and dead fish—to water bodies containing aquaculture cages. Cage aquaculture discharges untreated nutrients and toxins into water bodies, which has ecological consequences. Additionally, the escape of farmed fish from cages can pose genetic and ecology threats to wild fish populations though competition and interbreeding. It is risky for escaped farmed fish to reproduce in the wild because their offspring have a high mortality rate (Das et al., 2021). A typical aquaculture effluent includes dissolved or suspended particles, as well as nutrients such as nitrogen, which contribute to eutrophication commonly happened in the cage culture. In intensive culture systems involving high densities, substandard water quality might pressure the cultivated species, making them more prone to disease. Other than the above, antibiotics also contribute to a significant proportion of chemical waste which is able to deteriorate the water quality (Dauda et al., 2019).
‘Fish farm with ponds under colorful sky at sunset’ by Tom Fisk used under a Pexels License
Shrimp aquaculture has had a severe influence on coastal ecosystems due to the destruction of mangroves and the resulting changes in biodiversity such as control erosion, unfavourable water quality, and damaging the breeding sites for aquatic life (Ariffin et al., 2019; MS Schuler et al., 2020). Mangroves grow along estuaries and beaches in around 124 states with tropical or subtropical climate (Noor & Abdul Maulud, 2022). In the 25 years between 1995 and 2020, a total of 36,000 km2 of mangroves were lost throughout all five continents. These mangroves were deforested for recreation, tourism, infrastructure building, and aquaculture purpose (mainly for shrimp pond). The construction of shrimp ponds necessitates the destruction of mangroves, and past experience has shown that an excessive number of farms clustered along the coast leads to decreased productivity, disease outbreaks, and the failure of the projects. The removal of mangrove for shrimp aquaculture could lead to global warming (Hargan et al., 2020). Recruitment has been disrupted as breeding sites and nursery zones have been destroyed, and native aquatic species populations have either migrated or killed totally, making it difficult to transition from aquaculture to fishing as a means of survival (Ayyam et al., 2019). Therefore, these above-mentioned issues underscore the need to consider alternatives for survivability of coastal ecosystem by implementing sustainable aquaculture practices.
Another concerning issue with aquaculture and challenge to it being sustainable, is the widespread use of wild caught feed. In order for fish to get omega 3’s and other essential nutrients, they need to eat a food source that has them. Often, aquaculture feeds include small bony fish such as anchovy from wild sources. It is essential to find a food source which is not from wild fish stocks in order to be a sustainable industry.
Innovative aquaculture solutions including polyculture which combines multiple culture organisms such as fish, invertebrates and seaweed, to act as a circular system where waste is being utilised by other organisms, as well as other science solutions are required to further reduce impact from aquaculture and sustainably grown production to feed the world.
This text (‘further impacts of aquaculture’) is from “Towards Sustainable Aquaculture: A Brief Look into Management Issues” by Noorashikin Md Noor & Siti Norliyana Harun, which is licensed under CC BY 4.0, except for the last two paragraphs, which has been added by Trish Corbett.
Solutions to build sustainable aquaculture
There are a number of different types of organisms cultured around the world ranging from fish, to invertebrates and algae. As we have seen above, there may also be a number of impacts associated with aquaculture methods and culture organisms. There are a number of ways that sustainable aquaculture can be achieved to grow protein and nutrition production, to feed a growing planet. Solutions include:
Fish Nutrition
In the past, there has been significant issues with wild caught fish being used in aquaculture. Associate Professor David Francis and his team have been working on solutions to providing nutritious aquaculture feeds which utilise sustainable feed sources for the past 20 years.
Polyculture and Integrated Multi-Trophic Aquaculture (IMTA)
Polyculture is the culture of more than one organism. “Integrated multi-trophic aquaculture (IMTA) employs material excreted by one cultured species as intake for other cultured species under the same system. Consequently, the combination of cultured species which given feed in the right amount along with species which can synthesise feed via inorganic sources such as seaweeds would emerge a balanced feeding ecology, taking carrying capacity, site selection, and food safety into consideration (Resende et al., 2021). Integrating species of plants together with aquatic animals can greatly enhance the aquaculture sustainability.”
This text is from “Towards Sustainable Aquaculture: A Brief Look into Management Issues” by Noorashikin Md Noor & Siti Norliyana Harun, which is licensed under CC BY 4.0
“IMTA system aims to achieve sustainable aquaculture development, by recycling aquaculture wastes such as food resources through co-cultivating the targeted species with others having different feeding habits in different trophic levels, and improving the efficiency and productivity of intensive monoculture systems.” (Zhang et al., 2019)
Image Text Version
Figure 1. Integrated multi-tropic aquaculture (IMTA) system; in tanks (A), in ponds (B) and in coastal waters (C).
Figure 1 presents a three-part flow diagram, with A demonstrating IMTA in tanks, B demonstrating IMTA in ponds and C demonstrating IMTA in coastal waters. Each is described below under A, B and C headings.
Figure 1, flow diagram A
Figure 1, flow diagram A shows a tank environment, with fish, suspended seaweed and a sandy floor which contains rooted seaweed and invertebrates. Fish feeds engage the fish culture, where fish produce both organic wastes and inorganic wastes, with their own pathways. In the organic waste pathway, organic wastes include carbon, is ingested by suspension feeders, such as oysters, entering the invertebrate culture. The invertebrate culture excretes inorganic P and N, which joins other inorganic waste in the inorganic waste pathway. In the inorganic waste pathway, inorganic wastes from the fish culture, including PO43-, NH3-N and NO2-N, alongside P and N produced in the organic waste pathway, enter the seaweed culture.
Figure 1, flow diagram B
Figure 1, flow diagram B shows a pond environment, carved into the soil with grass on either side. There are vegetables growing on floating trays above water, various fish and water column feeder species including planktivorous and piscivorous (perch and carp), microalgae, zooplanktons, submerged plants anchored to the ground and, on the sea floor, bivalves and other molluscs. Fish feeds enter a contained fish system, where fish produce both organic wastes and inorganic wastes, with their own pathways.
In the inorganic waste pathway, fish excrete inorganic wastes (such as NH3-N), which is used by vegetable, microalgae and aquatic plants, such as zooplankton, which produce NO2-N, processed into PO43-, which is used by vegetables growing on floating trays in the pond. These vegetables will also extract inorganic wastes (PO43-, NH3-N, NO2-N and PO4-P) which are used by microalgae and aquatic plants.
In the organic waste pathway, Organic wastes (such as faecal material, uneaten fish feed) are extracted by molluscs, entering the bivalve culture.
Figure 1, flow diagram C
Figure 1, flow diagram C shows a marine environment, where fish are contained in aquaculture. The environment features suspension extractive aquaculture with seaweed and shellfish close to the surface, and deposit extractive aquaculture with invertebrates and both deposit and suspension feeders close to the sea floor.
Fish feeds enters a contained fish aquaculture, there are two pathways: fish excretion and fish egestion.
In the fish egestion pathway, particulate organic carbon from fish egestion may sink to the ocean floor and either become resuspended in water or get ingested by deposit feeders, like sea cucumbers or suspension feeders, like sea urchins. Suspension feeders and deposit feeders may either push their excretions into the excretion pathway or egest matter into the ocean floor.
In the fish excretion pathway, inorganic phosphorous and nitrogen are suspended in the ocean – either via fish excretions, excretions from deposit feeders or suspension feeders or resuspension (or release) of materials from the ocean floor. Inorganic phosphorous and nitrogen (as NO3-N and NH3-N) may enter uptake pathways by nutrient absorbers as PO43-, like seaweed.
End Image Text Version
This image and its associated caption is from “Water quality management in aquaculture” by © Fatimah M. Yusoff, Wahidah A. D. Umi, Norulhuda M. Ramli and Razif Harun, 2024. Published by Cambridge University Press, is licensed under CC BY 4.0.
Watch the video below to hear about an example of IMTA Vertical ocean farming.
Aquaponics
Aquaponics is a sustainable and innovative agricultural method that combines aquaculture and hydroponics in a mutually beneficial system. It’s a closed-loop system that allows the symbiotic relationship between fish and plants to create a self-sustaining ecosystem. The majority of aquaponics utilise freshwater systems and plants.
Activity: Aquaponics
Listen to Antonio Paladino discuss Aquaponics in Action on the Aqua Culture Podcast to learn more about how these systems work!
Ecologically beneficial outcomes possible via aquaculture
Sustainable aquaculture does not only have the potential to help solve the global food crisis, it may also have a number of other ecological benefits. New research from Overton et al. (2022) has indicated there are at least 12 ecologically beneficial outcomes able to be achieved through aquaculture. If you are interested to learn more, explore the article by Overton et al. below.
Image Text Version
Figure 2: The 12 ecologically beneficial outcomes that can be achieved through aquaculture
Figure 2 is a diagram entitled ‘The 12 ecologically beneficial outcomes that can be achieved through aquaculture. A particular aquaculture activity may deliver several of these outcomes at once’. These outcomes are:
- Habitat protection
- Ex situ conservation
- Wild harvest replacement
- Habitat rehabilitation
- Removal of overabundant species
- Habitat restoration
- Coastal defense
- Bioremediation
- Assisted evolution
- Climate change migration
- Species recovery
- Biological control
End Image Text Version
“Achieving conservation and restoration outcomes through ecologically beneficial aquaculture” by Kathy Overton, Tim Dempster, Stephen E. Swearer, Rebecca L. Morris, & Luke T. Barrett is licensed under CC BY 4.0
The Australian National Aquaculture strategy aims to: “double the current value of the current value of Australia’s aquaculture industry to $2 billion per year by 2027”. To do this, Australian aquaculture production needs to grow by 7 percent between 2017 – 2027 (Department of Agriculture and Water Resources, 2017).
This text is from “National Aquaculture Strategy (September 2017)” by © Commonwealth of Australia, which is licensed under CC BY 4.0
Activity:
Type your exercises here.
Activity Text Version
Activity: Test your Knowledge
This exercise invites readers to answer questions to test their knowledge, based on the aquaculture information above. Questions and answers are listed below.
Question 1
Recirculating Aquaculture Systems (RAS):
Select the best option from:
- involves cages in the ocean where the fish circulate around the cage and are fed a pelletised feed
- involves a series of tanks on land where water is continually recycled through the system and is treated by a range of biological and mechanical methods to ensure the water in the facility is clean as it recirculates through the system
- involves organisms that filter feed on the water coming in from the ocean. The water is passed through the system and then released back into the ocean as more water comes in and is circulated between the ocean and the RAS facility
- are a series of ponds that use water from the ocean and discharge it back to the ocean after it has passed through the system
Answers to question 1
- involves a series of tanks on land where water is continually recycled through the system and is treated by a range of biological and mechanical methods to ensure the water in the facility is clean as it recirculates through the system
Question 2
Active feeding systems are open ocean systems:
Select the best option from:
- where multiple organisms are cultured together so that waste is circulated and utilised by other organisms
- where filter feeding organisms like mussels are not actively fed and instead gain their nutrition from the environment
- where organisms such as salmon are cultured and fed their diet, often in pelletised from
- where fish are freely released into the ocean to breed and grow to be caught later
Answers to question 2
- where filter feeding organisms like mussels are not actively fed and instead gain their nutrition from the environment
Question 3
Historically, there have been a number of impacts of aquaculture on the environment. Select all impacts below that are related to aquaculture.
Select all that apply from:
- excess nutrients from excess feed and waste products from the cultured organism, resulting in eutrophication
- clearing of habitat such as mangroves
- feed produced from wild caught fish
- cadmium poisoning
Answers to question 3
- excess nutrients from excess feed and waste products from the cultured organism, resulting in eutrophication
- clearing of habitat such as mangroves
- feed produced from wild caught fish
Question 4
Which of the following best describes Integrated multi-trophic aquaculture
Select the best option from:
- multiple species are farmed in a recirculating aquaculture system
- utilising a single species to filter feed excess nutrients from the environment
- multiple species of different trophic levels are cultured together in a 3D circular system where wastes are recycled as a food resource by another organism
- using multiple fish species in one cage ranging from benthic feeders to pelagic
Answers to question 4
- multiple species of different trophic levels are cultured together in a 3D circular system where wastes are recycled as a food resource by another organism
End Activity Text Version
References
Ariffin, F. D., Halim, A. A., Hanafiah, M. M., Awang, N., Othman, M. S., Azman, S. A. A., & Bakri, N. S. M. (2019). THE EFFECTS OF AFRICAN CATFISH, CLARIAS GARIEPINUS POND FARM’S EFFLUENT ON WATER QUALITY OF KESANG RIVER IN MALACCA, MALAYSIA. Applied Ecology & Environmental Research, 17(2).
Ayyam, V., Palanivel, S., & Chandrakasan, S. (2019). Mangroves and sustainable development of the coastal region. In Coastal Ecosystems of the Tropics-Adaptive Management (pp. 529-550). Singapore: Springer Singapore. https://link.springer.com/chapter/10.1007/978-981-13-8926-9_23
Das, S. K., Tou, W. X., Noor, N. M., De, M., & Samat, A. (2021). Length-weight relationship, condition factor, and age estimation of commercially important trawl species from Mersing coastal waters, Johor, Malaysia. Sains Malaysiana, 50(1), 1-7.
Dauda, A. B., Ajadi, A., Tola-Fabunmi, A. S., & Akinwole, A. O. (2019). Waste production in aquaculture: Sources, components and managements in different culture systems. Aquaculture and Fisheries, 4(3), 81-88. https://www.sciencedirect.com/science/article/pii/S2468550X18300352
Department of Agriculture and Water Resources. (2017). The National aquaculture strategy. The Commonwealth of Australia. https://www.agriculture.gov.au/agriculture-land/fisheries/aquaculture/national-aquaculture-strategy
FAO. (2022). Fishery and Aquaculture Statistics. Global Aquaculture Production 1950–2020 (FishStatJ). In FAO Fisheries and Aquaculture Division; FAO: Rome, Italy, 2022.
Hargan, K. E., Williams, B., Nuangsaeng, B., Siriwong, S., Tassawad, P., Chaiharn, C., … & Los Huertos, M. (2020). Understanding the fate of shrimp aquaculture effluent in a mangrove ecosystem: Aiding management for coastal conservation. Journal of Applied Ecology, 57(4), 754-765. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.13579
Md Noor, N., & Harun, S.N. Towards Sustainable Aquaculture: A Brief Look into Management Issues. Appl. Sci. 2022, 12, 7448. https://www.mdpi.com/2076-3417/12/15/7448
Noor, N. M., & Abdul Maulud, K. N. (2022). Coastal vulnerability: a brief review on integrated assessment in Southeast Asia. Journal of Marine Science and Engineering, 10(5), 595. https://www.mdpi.com/2077-1312/10/5/595
Noor, N. M., & Das, S. K. (2019). Effects of elevated carbon dioxide on marine ecosystem and associated fishes. Thalassas: An International Journal of Marine Sciences, 35(2), 421-429. https://link.springer.com/article/10.1007/s41208-019-00161-3
Peay, S., Johnsen, S. I., Bean, C. W., Dunn, A. M., Sandodden, R., & Edsman, L. (2019). Biocide treatment of invasive signal crayfish: successes, failures and lessons learned. Diversity, 11(3), 29. https://doi.org/10.3390/d11030029
Resende, L., Flores, J., Moreira, C., Pacheco, D., Baeta, A., Garcia, A. C., & Rocha, A. C. S. (2021). Effective and low-maintenance IMTA system as effluent treatment unit for promoting sustainability in coastal aquaculture. Applied Sciences, 12(1), 398. https://doi.org/10.3390/app12010398
Schuler, M. S., Hintz, W. D., Jones, D. K., Mattes, B. M., Stoler, A. B., & Relyea, R. A. (2020). The effects of nutrient enrichment and invasive mollusks on freshwater environments. Ecosphere, 11(10), e03196. https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.3196
Verdegem, M., Buschmann, A. H., Latt, U. W., Dalsgaard, A. J. T., & Lovatelli, A. (2023). The contribution of aquaculture systems to global aquaculture production. Journal of the World Aquaculture Society,54(2), 206–250. https://doi.org/10.1111/jwas.12963
Zhang, J., Zhang, S., Kitazawa, D., Zhou, J., Park, S., Gao, S., & Shen, Y. (2019). Bio-mitigation based on integrated multi-trophic aquaculture in temperate coastal waters: practice, assessment, and challenges. Latin american journal of aquatic research, 47(2), 212-223.
