Sustainable diets to support the growth of shellfish aquaculture industry – MIDSA

In this case study you will learn about:

1. The challenges with current aquaculture bivalve shellfish diets and why it’s preventing industry growth
2. Why microencapsulated algal diets provide an excellent replacement solution
3. The features and benefits of the new microcapsule diets designed for mussels and oysters arising from an EIT Food supported project

Many shellfish farmers are looking for methods to reduce bivalve production costs and increase production output, while contributing to the continued growth of the bivalve aquaculture industry. We introduce a new nutritionally enhanced microencapsulated bivalve shellfish diet that supports bivalve growth, is cost-effective and is sustainably produced from organic waste streams.

The challenge – producing bivalve for aquaculture uses live algae as feed which can be expensive and unreliable

Bivalve shellfish such as clams, scallops, oysters, and mussels offer several benefits to human health and provide a high protein content with a rich source of essential fatty acids and micronutrients. Their production also has a lower environmental footprint compared with other land-based animals and many crop plant (1). As a result, many of us are including more shellfish in our diets.

While shellfish production has traditionally taken place in coastal intertidal zones, sustainable shellfish farming is now driving the implementation of offshore aquaculture, which can support a faster growth of farmed fish and shellfish species (2).

In fact, the global bivalve industry now accounts for approximately 25% of aquaculture and was worth over USD $29.8 billion in 2020. However, growth in the bivalve industry is lagging behind other areas of aquaculture such that production increased just 2.7% per year over the last decade, compared to 8.4% for finfish aquaculture (3). This slow growth is due to production issues associated with suboptimal feeding procedures, disease control and low-quality product and taste.

Originally, juvenile bivalves, also known as “spat”, were captured from natural areas in the wild to supply hatcheries. However, overexploitation of this process has led to a reliance on a supply of juveniles produced by adult broodstock in hatcheries (4).

In terms of dietary requirements, bivalves need a range of dietary proteins (13-20%), carbohydrates (5-20%) and essential fatty acids for them to grow and survive (5). While some commercial bivalve feeds such as powders or emulsions are available, often they have an inadequate nutrient profile and limitations as a delivery system. Therefore, broodstock produced in most hatcheries are fed live microalgae.

However, production of live microalgae is a highly inefficient regarding the use of land and energy. For example, typical hatcheries require 400 square meters of algal tanks to maintain just 400 broodstock, and they require high-intensity artificial lighting and climate control systems to support algal growth (6,7). Additionally, algal cultures are difficult to maintain, vary in quality, and prone to loss caused by contamination and disease, resulting in disrupted supplies. Also, there is an increased disease risk for the cultured bivalves.

The solution – formulated algal-derived microencapsulated powdered diets provide a sustainable alternative

New advances in algal and microencapsulation technology have enabled the manufacture of a powdered artificial feed, thereby removing the requirement of hatcheries to produce their own live algae feed. Importantly, nutrients that are used in these novel diets can come from micro- and macroalgae grown on low-cost food waste or organic side streams of existing aquaculture systems. These algal feeds are more sustainable because they are produced through a circular economy approach, which is a central goal in the current strategies of “blue growth” of global aquaculture.

This EIT Food’s project (MIDSA) demonstrated that the microalgae Schizochytrium sp can be grown from effluents of existing aquaculture systems or the macroalgae Undaria pinnatifida (wakame) can be cultured using low-cost food industry organic side-streams and then further processed to create microencapsulated inert nutritional-rich particles (8,9). Learn more about the project below.

Schizochytrium and Undaria pinnafida were selected to produce the microencapsulated diets as they have different but complementary nutritional profiles to attain bivalve nutritional requirements, so can therefore be combined if required. For example:

• Schizochytrium provides key nutrients such as the omega-3 fatty acids including eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), the latter exceeding 20% dry weight, over twice the abundance of DHA in hatchery-grown algae.

• Undaria pinnatifida is rich in dietary fibers, has a good protein quality in terms of amino acids composition and contains elevated C-18 polyunsaturated fatty acid precursors.

The new microencapsulated diets were tested with mussel (Mytilus galloprovincialis) spats against commercial algal feeds (10). They demonstrated excellent results in growth and survivorship, improved bivalve nutritional status and an acceptable taste.

The findings indicated that a viable product could be produced at commercial scale.

• A microencapsulated Schizochytrium algae diet was produced on an industrial scale for $1.50 per kg, using low-cost food waste and organic side-streams as inputs. This bivalve feed provides a 140-fold/significant saving on the current cost of $220 per kg associated with growing live algae to feed broodstock.

• Viability analysis demonstrated that encapsulated products achieved desired results on mussel spat whilst costing 10 times less than the market leading alternative (Reed Mariculture Shellfish Diet 1800).

• Compared to fish farming it was estimated that every tonne bivalve protein produced spares 9 hectares, 67 tonnes of CO2, and 40,000 litres of freshwater.

Microencapsulation technology offers advantages over live algal feeds or alternative artificial inert diets. Examples include:

1. Nutritional profile: A single microencapsulated feed particle can be tailored to create an optimal formulation of key nutrients for bivalve growth. This includes high levels of protein and polyunsaturated fatty acids including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).
2. Customisable: The diet can be customised to match species specific nutritional requirements.
3. Controls disease: The particles can include therapeutics or disease control agents.
4. High retention: Microparticle size and buoyancy can be tailored to bivalve preferences for maximum retention efficiency, and buoyancy can be optimised to ensure particles remain within reach of feeding bivalves. This is an advantage over other artificial nutrient systems such as powders, which tend to float on the water surface, and can clump into particles too large to be retained by bivalves.
5. Minimal nutrient loss: Encapsulates can be designed to minimise nutrient loss prior to ingestion e.g. lipid coatings allow delivery of low molecular weight, water soluble compounds with minimal leaching to the surrounding water thereby retaining particle nutrients until they are released by the digestive processes of the bivalve.
6. Long term storage: Microparticles are stable in air thereby enabling storage of high-quality feeds for long time periods and are less likely to become contaminated over time by bacteria than live algal cultures, and the costly process of synchronizing microalgal feedstock to match bivalve production is avoided.

As an outcome of EIT Food’s project, microencapsulation technology can offer an efficient way to deliver diets that could improve bivalve shellfish nutrition, growth, and production output, while reducing bivalve mortality, production costs, and financial risks.

As a next step, the project team is collating data to demonstrate that their microencapsulated algal-derived product is commercially viable and is working on developing a clear route to market via major suppliers in the aquaculture industry.

University of Cambridge, UK (lead organization)

World-leading University whose mission is to contribute to society through the pursuit of education, learning, and research at the highest international levels of excellence. Tasks included the production and testing of microcapsules, support with experimental design, data analysis product testing, commercial viability analysis, protection of IP, customer perception evaluation.

AZTI

AZTI transforms science into solutions that respond to the great challenges of the food value chain. Responsible for supplying bivalve juveniles (spat) and broodstock and carrying out trials of products in lab and upscaled facilities. Tasks included the experimental formulation of microdiets, design and monitoring of growth trials, statistical analysis, and assessment of final mussel composition for consumer acceptance.

Matis

Matis is an independent, governmentally owned, food and biotech R&D company headquartered in Iceland. Tasks included the testing of products against bivalve larvae and broodstock in hatchery facilities.

Rethink Resource

Rethink Resource is an innovation agency for side-streams and upcycling. Tasks included identifying a sustainable source of nutrients from waste streams.

1. Aquaculture 2019. Microencapsulated diets to improve growth and survivorship in juvenile European flat oysters ( Ostrea edulis )
2. Aquaculture 2020. Biological, socio-economic, and administrative opportunities and challenges to moving aquaculture offshore for small French oyster-farming companies
3. FAO 2022. The State of the World Fisheries.
4. Goods and Services of Marine Bivalves 2018. Global Challenges of Marine Bivalves. Trends and Challenges.
5. Reviews in Fisheries Science 2007. A review of the nutritional requirements of bivalves and the development of alternative and artificial diets for bivalve aquaculture
6. Seafish Report 2017. Closing the circle report II: Development of a generic shellfish hatchery design with associated spatting ponds.
7. Global Seafood Alliance 2021. Development, testing of microencapsulated Schizochytrium feeds for bivalve broodstock
8. Scientific Reports 2020. Microencapsulated algal feeds as a sustainable replacement diet for broodstock in commercial bivalve aquaculture
9. Campanati, C., Arantzamendi, L., Zorita, I., Juez, A., & Aldridge, D. C. (2023).Microencapsulated diets using thraustochytrids and macroalgae side streams for nursery rearing of Mytilus galloprovincialis spat. Journal of the World Aquaculture Society,54(4), 994–1012.https://doi.org/10.1111/jwas.1...
10. Campanati C., Arantzamendi L., Zorita I., Briaudeaud T., Lekube X., Izagirre U., David C.A. (2023). Nutritional effect of microalgal concentrates substitution with microencapsulated diets in Mytilus galloprovincialis spat. Aquaculture (576), 739879.https://doi.org/10.1016/j.aquaculture.2023.739879