by Joly Ghanawi, International Aquafeed and Fish Farming Technology
Fishmeal has long been one of the most valuable ingredients in aquaculture feeds. Its high protein content, balanced essential amino acid profile, digestibility and palatability make it particularly well suited to the nutritional requirements of farmed aquatic species, especially carnivorous fish. Yet these advantages come with an increasingly important constraint: supply.
Aquafeed accounts for a substantial share of global fishmeal consumption, while production is vulnerable to environmental conditions and pressure on marine resources. El Niño events have contributed to instability in fishmeal availability, adding to concerns about scarcity, fluctuating prices and security of supply. This is encouraging greater interest in alternative proteins that could reduce aquaculture’s dependence on conventional marine ingredients.
The challenge is that replacing fishmeal is not simply a matter of finding another high-protein ingredient. A successful alternative also needs an appropriate amino acid profile, good digestibility and palatability, competitive cost, reliable availability and a manageable environmental footprint.
Plant proteins offer scale
Plant proteins are already among the most widely used fishmeal alternatives. Soybean meal, wheat and maize products, rapeseed, sunflower, cottonseed, peas, beans and lupins all have potential applications in aquafeed. Their principal advantages are relatively wide availability and reasonable cost, making them considerably easier to source at scale than many newer protein ingredients.
Soybean meal is particularly important. It has a relatively balanced amino acid profile and provides lysine, tryptophan, threonine and isoleucine, nutrients that can be limited in cereal ingredients. Processing can further improve its suitability. Fermentation, for example, can reduce anti-nutritional compounds including phytates, tannins and phenols, potentially improving the nutritional characteristics of soybean products.
However, plant proteins also demonstrate why protein content alone is a poor measure of an ingredient’s suitability. Anti-nutritional factors can interfere with nutrient utilisation and palatability, while high levels of plant ingredients can adversely affect feed intake, growth and intestinal health. Soybean meal can also cause intestinal irritation, illustrating the need to consider gut health alongside growth and feed conversion when determining suitable inclusion rates.
Making more of animal by-products
Animal-derived proteins provide another established route away from fishmeal. Poultry by-product meal, feather meal, meat and bone meal, blood meal and haemoglobin products can all supply substantial amounts of protein. Their use also offers an opportunity to recover nutrients from existing animal-production streams rather than allowing potentially valuable materials to go unused.
Their suitability nevertheless depends on both the raw material and processing. Nutritional quality, digestibility and palatability can vary, meaning that an ingredient that performs well at moderate inclusion may become less effective as its proportion of the diet rises. This pattern is not unique to animal proteins: across both plant- and animal-derived alternatives, inclusion levels have varied considerably, and excessive substitution can adversely affect growth, metabolism and other biological parameters.
Insects emerge as a novel option
Insect meals, including black soldier fly larvae and mealworms, are among the newer ingredients being investigated for aquafeed. Their potential lies in providing an animal-derived protein without relying directly on conventional fishmeal.
Evidence also suggests that the effects of insect ingredients can extend beyond basic nutrition. In one 12-week feeding study cited in the source material, higher levels of defatted black soldier fly larvae meal were associated with changes in several non-specific immune markers and anti-inflammatory responses.
As with other alternatives, however, suitability cannot be generalised across every species and diet. The effects of fishmeal replacement are strongly dependent on both the ingredient and the level at which it is included. This makes consistency and appropriate formulation particularly important if insect proteins are to assume a larger role.
Algae and microbial proteins expand the protein pool
Algae and single-cell proteins broaden the range of options still further. Microbial proteins can be produced from organisms such as bacteria and yeasts, while microalgae such as Chlorella vulgaris have also been investigated as substitutes.
These ingredients are particularly interesting because their effects can differ markedly from those of conventional plant proteins. When Chlorella vulgaris, Clostridium autoethanogenum protein and cottonseed protein concentrate were evaluated as fishmeal substitutes in largemouth bass, the algal and microbial proteins were associated with greater abundance of some beneficial intestinal bacteria than the cottonseed treatment. The algal protein also avoided some of the changes in intestinal villi observed with the other substitutions.
Methanotroph bacterial meal provides another example. Different inclusion levels produced changes in digestive enzyme activity and intestinal bacteria, demonstrating both the potential of microbial proteins and the importance of establishing appropriate inclusion rates.
Formulation may matter more than finding a single winner
No alternative perfectly reproduces all the characteristics of fishmeal. Plant ingredients may be economical and readily available but can introduce amino acid imbalances, anti-nutritional factors and palatability problems. Other novel proteins may offer attractive nutritional characteristics but still require careful management of inclusion rates and consistency.
Feed formulation can compensate for some of these weaknesses. Crystalline amino acids can correct deficiencies in alternative proteins, while enzymes such as phytase, protease and carbohydrase can improve nutrient digestibility and break down anti-nutritional components. Attractants can encourage feed intake, and probiotics, prebiotics and other functional compounds can support intestinal health and nutrient absorption.
This also makes combinations of proteins particularly significant. Blending ingredients can create a more favourable amino acid profile than depending upon a single substitute, while allowing formulators to exploit the advantages of different raw materials.
Against the backdrop of El Niño, diversity becomes increasingly valuable. Alternative proteins are not simply competing to replace fishmeal kilogram for kilogram. They can provide aquafeed producers with a broader range of ingredients from which to formulate diets when marine protein availability becomes constrained.
The direction of travel is therefore towards diversification. Rather than one novel ingredient becoming the new fishmeal, future aquafeeds are likely to combine conventional and emerging protein sources, supported by increasingly precise formulation. El Niño and associated fishmeal supply uncertainty could accelerate that transition by making resilience, alongside nutrition, cost and sustainability, an increasingly important measure of an aquafeed ingredient’s value.
For references, contact editorial@perendale.co.uk
