Novel feed ingredients can help meet the nutritional needs of farmed fish

Meeting the nutritional needs of farmed fish is necessary to ensure feed efficiency, fish health, and cost-effectiveness in aquaculture production. While the nutritional needs of fish vary by species and life stage, all fish require a mix of macro and micronutrients to thrive. Traditionally, fish meal and fish oil (FMFO) have provided key nutrients for farmed fish, but increasing scarcity, price volatility, and environmental impacts are necessitating their replacement in aquafeed formulations. While there are concerns about how to replace FMFO in aquafeed without compromising fish nutrition, the science of fish nutrition reminds us that fish do not inherently need these ingredients, rather only the nutrients they contain. With the appropriate feed formulations and careful attention to nutrient digestibility, novel feed ingredients can help to meet the nutritional needs of farmed fish while reducing dependence on FMFO. 

What are the nutritional needs of farmed fish? 

Just like wild fish, farmed fish need several essential nutrients to both survive and thrive. In the world’s ocean ecosystems, energy and nutrients flow upwards as lower trophic species (e.g., plankton, forage fish) are consumed by higher trophic species (e.g., carnivorous fish, aquatic mammals) in the food chain (Figure 1). 

(Figure 1: Trophic flows of energy in marine ecosystems. Image courtesy: Pew Charitable Trusts)

Farmed fish obtain essential nutrients through feed (‘aquafeed’). Beyond providing essential nutrients, which are also necessary for wild fish, aquafeed formulations are also designed to maximise farmed fish productivity (i.e., yield). Thus, aquafeed formulations must combine the appropriate blend of key macronutrients (i.e., carbohydrates, lipids (fats), and protein) and micronutrients (e.g., amino acids, minerals, vitamins) to ensure that fish both grow rapidly and remain healthy. 

Macronutrient needs of farmed fish

The nutritional needs of farmed fish vary by species and life stage. Life stages of farmed fish generally include moving from juvenile stages (e.g., fry, fingerlings, juveniles) to adult stages (e.g., grower, broodfish). Across life stages, juvenile fish tend to require higher levels of protein and fat, often in excess, to grow compared to adult fish (Figure 2). For example, diets for juvenile carnivorous species require 47-52% protein and 14-16% fat, with only 15-25% carbohydrates. As adults, carnivorous species require less protein (45-47%) and fat (10-12%), but more carbohydrates (25%). Similar trends across life stages exist for omnivorous fish (Figure 2). 

(Figure 2: Dietary macronutrient levels in carnivore and omnivorous fish across life stages. Recommended dietary nutrient levels are measured in % minimum of feed for crude lipids and protein, and % maximum of feed for carbohydrates. Created with data from FAO.)

Across species, carnivorous fish like salmon, trout, and seabass tend to require more protein and fat (Figures 2-3), while omnivorous fish, like carp and tilapia, have higher carbohydrate requirements (Figures 2-3). For example, most adult carnivorous species require 25% carbohydrates in adult diets, while adult omnivorous species require 40% (Figures 2-3). 

(Figure 3: Macronutrient needs for adult fish by species. Common carps and tilapia are omnivorous, while shrimp and salmon are carnivorous. Adapted from data from Hatch Innovation Services.)

Micronutrient needs of farmed fish

Similar to macronutrients, micronutrient requirements in aquafeed also vary by species and lifestage. However, regardless of specific volume, these micronutrients play a similar role in fish health and growth across species. For example, essential amino acids help to improve growth and protect fish against infections, while vitamins and minerals are necessary for digestive health and development (Table 1). Ultimately, the goal of aquafeed is to provide holistic nutrition to farmed fish that supports health, productivity, and cost-effectiveness. 

(Table 1: The role of micronutrients in fish health. Adapted from Yuru et al (2020).)

Conventional sources of nutrition in aquafeed

Historically, a number of animal- and plant-based ingredients have been used in aquafeed formulations to deliver high-quality nutrition to farmed fish. In particular, wild-caught forage fish are caught to produce FMFO, especially to feed carnivorous species like salmon and trout.  FMFO is regarded as a high-quality source of protein and essential omega-3 fatty acids, like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). 

Part of what makes FMFO widely used in aquafeed is that it is highly digestible. Digestibility is the portion of a specific feedstuff or nutrient (like protein) that exits the digestive system and is absorbed into the bloodstream. The high digestibility of FMFO results in a large fraction of FMFO being converted into growth and body mass for farmed fish. Over time, improved aquafeed formulations have increased the digestibility of feed, leading to increased feed conversion ratios (FCRs) for farmed fish. This improvement has led to a decrease in the number of wild-caught fish necessary to produce a single farmed fish over time. 

However, increasing aquaculture production to meet rising demand for fish and seafood will require larger volumes of wild-caught fish for feed, despite improvements in feed use efficiency. Combined with challenges in FMFO supply chains, like scarcity, price volatility, and climate change, FMFO is increasingly costly and vulnerable. As a result, there is increasing pressure for the aquafeed industry to transition to more sustainable feed alternatives. 

Case study: Algal oil can help to meet the nutritional needs of farmed fish

CFI’s recent State of the Industry Report on Algal Oils provides a key example of how novel ingredients can meet the nutritional needs of farmed fish without reliance on FMFO. Algal oils are lipids derived from specific microalgae that naturally synthesise the same long-chain omega-3 fatty acids, EPA and DHA, that occur in fish oil. 

Across leading microalgae strains, lipids can comprise more than half of algal dry mass, with EPA and DHA together making up as much as 55% of total fatty acids. EPA and DHA levels in algal oil are often comparable to, or exceed, premium fish oils. Numerous research trials and commercial tests have also demonstrated that algal oils can be included up to 36% and replace fish oil up to 100% in aquafeeds without compromising growth or feed efficiency. 

(Table 2.  Maximum viable inclusion rate of microalgae products in fish and shrimp)

*indicates inclusion rate where 100% of fish oil was replaced in the feeding trial.

^ For Isochrysis inclusion levels, refer to whole-cell biomass used as combined lipid and protein sources, not solely as fish-oil replacements. 

Ultimately, while conventional ingredients can offer valuable nutritional benefits, the addition of novel ingredients in the right combinations can help to meet the nutritional needs of fish with fewer risks. Algal oils have demonstrated nutritional equivalence to fish oil with fewer safety risks and more sustainability benefits. Aquafeed producers increasingly recognise that algal oils can meet EPA and DHA requirements without compromising growth, feed efficiency, or product quality. Continued advances in strain selection and cultivation will enable producers to fine-tune omega-3 ratios and extend applications across more aquaculture species.

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