Internationally, alternative ingredients to fish meal and oil for the production of aquaculture feeds continue to be sought after. There are a variety of vegetable ingredients with a relatively high protein content.
Recent studies have shown that microalgae can replace fish meal and oil in aquaculture feeds, while maintaining sustainability standards.
A team of researchers from Deakin University, Nord University, and Patuakhali Science and Technology University published information on the potential use of microalgae as a sustainable and environmentally friendly source of nutrients for aquaculture.
The study summarizes the current state of knowledge on the general attributes of various species of microalgae and their nutritional properties. The document also includes possible topics for future research that could lead to advances in the microalgae-based aquaculture business.
Processing of microalgae to produce inputs
Water represents about 99.8% – 99.9% of microalgae biomass. In this sense, it is essential that a microalgae producer has an efficient dehydration infrastructure to improve microalgae harvesting.
Microfiltration and centrifugation technologies are commonly used in microalgae cultivation facilities.
Drying is an effective method for acquiring an algae product that can be stored for later use. However, drying processes are expensive, and the chosen technology will have a significant impact on production profitability.
Microalgae meal can be directly used in fish feeding, especially if the algae cell wall is broken to maximize nutrient accessibility.
On the other hand, microalgae lipids can be extracted using a variety of methods. These methods can be classified as: (a) mechanical methods such as pressing, homogenization, grinding, and ultrasonic-assisted extraction, and (b) chemical methods such as extraction with hexane solvents.
Nutritional profile of microalgae
Several microalgae have been investigated for their use in formulating aquaculture feeds, as a source of protein, lipids, vitamins, and carotenoids for shrimp and carnivorous fish species.
However, since microalgae are relatively new ingredients for formulated aquaculture feeds, there is a shortage of data on the quality of proteins and lipids of the large number of microalga species produced.
Microalgae typically consist of 30% to 40% protein, 10% to 20% lipids, and 5% to 15% carbohydrates. They are also abundant in trace elements such as calcium, magnesium, phosphorus, iron, iodine, and zinc, and are rich in polyunsaturated fatty acids.
These health-promoting compounds make microalgae suitable for use as natural supplements in fish feed.”
Role of microalgae in aquaculture production
Microalgae of the genera Chlorella, Nannochloropsis, Tetraselmis, Arthrospira, Pavlova, Haematococcus, and Thalassiosira are some of the most commonly used in aquaculture production.
The potential effects of supplementing microalgae in aquaculture feeds on larval performance, food assimilation and utilization, growth performance, immunity, and disease resistance of fish and shellfish are highlighted in the study.
Feasibility of microalgae biomass use
A significant challenge for the use of microalgae as aquaculture feed ingredients is their high production cost, when compared to the bulk of ingredients in aquaculture production.
In fact, 1 kg of Chlorella sorokiniana meal has a price of US$2.65 to replace fishmeal, and US$0.66 to replace soybean meal in tilapia diets.
In particular, before being truly viable, the price of microalgae must reach a position where the nutrients offered are comparable to those provided by other raw materials.
Additionally, it is evident that several factors must be considered before microalgae can be used as a main ingredient in aquaculture feeds: (a) availability of microalgae versus demand; (b) palatability and digestibility of feed for microalgae; and (c) processing techniques affordable by fish feed manufacturers.
Microalgae can be incorporated into aquaculture feeds in a variety of methods to increase aquaculture production.
Challenges of using microalgae in aquaculture feeds
Microalgae are promising feed ingredients, as they provide major nutrients, micronutrients, and essential nutrients with health-promoting properties.
The study authors identify the following challenges:
- High cost of microalgae production. Production cost is associated with low productivity in photobioreactors or large-scale open ponds, energy-consuming collection/dehydration procedures, and low-cost processing techniques.
- Improper and inadequate drying can have an adverse impact on nutritional and physical properties, greatly reducing the value of microalgae as fish feed ingredients.
- Several studies have explored the production of microalgae biomass in wastewater, leachates, or certain industrial or aquaculture effluents. However, a comprehensive safety evaluation is needed for aquaculture feeds generated from biomass cultivated in wastewater.
- Microalgae often have thick cell walls that prevent digestive enzymes from working on nutrients embedded in cells. Different techniques have been tried to increase the nutrient availability of microalgae biomass, but bioavailability seems to be a limitation even when cell walls are broken.
- Various environmental conditions, such as light, temperature, and pH, have a significant impact on biomass productivity. Biotechnological research is seeking solutions for more cost-effective production of microalgae biomass.
Conclusion
Microalgae represent sustainable alternatives to various commercially used food ingredients in aquaculture due to their nutritional and functional properties.
However, microalgae-based diets have not been used to their full potential due to the high costs associated with production, harvesting, processing, and nutrient extraction.
More studies are needed to examine the feasibility of various microalgae as possible food ingredients to support growth and health.
Contacts
Muhammad A. B. Siddik
School of Life and Environmental Sciences
Deakin University
Geelong, Victoria,
Australia
Email: s.siddik@deakin.edu.au
Mette Sørensen
Faculty of Biosciences and Aquaculture
Nord University
Bodø, Norway.
Email: mette.sorensen@nord.no
Reference (open access)
Siddik, MAB, Sørensen, M, Islam, SMM, Saha, N, Rahman, MA, Francis, DS. Expanded utilisation of microalgae in global aquafeeds. Rev Aquac. 2023; 1- 28. doi:10.1111/raq.12818
