Insect meals in aquafeed: formulate before replacing

Insect meals are frequently presented as direct substitutes for fishmeal. The evidence supports a more practical conclusion: they are a family of ingredients whose value changes with insect species, rearing substrate, harvest stage, defatting, drying and the final diet. A successful inclusion rate cannot be judged from the replacement percentage alone. It must preserve the fish’s nutritional requirements, pellet quality, stock performance and the composition of the harvested product.

One category, many different ingredients

Black soldier fly (Hermetia illucens) and yellow mealworm (Tenebrio molitor) are the most widely investigated species, but their meals are not interchangeable. Protein and lipid content varies with larval diet and processing. A full-fat meal carries more lipid, whereas defatting generally concentrates protein. Heat improves safety and storage stability, but poorly controlled processing can also reduce the availability of selected amino acids.

Fishmeal supplies more than crude protein. It provides digestible amino acids, marine lipids, minerals and compounds that influence palatability. Replacing one kilogram of fishmeal with one kilogram of insect meal without reformulating the rest of the diet can create a methionine shortfall, alter fatty-acid balance or reduce EPA and DHA deposition in the fillet. Decisions therefore need to follow available nutrients, not the ingredient’s headline protein value.

What recent evidence can—and cannot—show

A meta-analysis in the Journal of Insects as Food and Feed retained 65 studies from 5,530 initially identified records. Thirty-two informed digestibility, 42 blood measurements and ten economic outcomes. On average, apparent protein digestibility was similar in insect-containing and control feeds, while dry-matter and lipid digestibility showed small disadvantages. Blood and immune responses varied considerably.

Those pooled estimates are not a universal inclusion recommendation. They combine fish species, insect products, processing methods and replacement levels. A 2025 review reports successful partial replacement in several freshwater and marine species, but it also identifies impaired growth, intestinal integrity or beneficial fatty-acid deposition when inclusion or composition becomes unsuitable. A result from Nile tilapia cannot be transferred directly to rainbow trout, European seabass or Atlantic salmon.

Chitin requires the same discipline. This exoskeleton component may influence gut microbial communities and selected immune responses, yet it may also reduce digestibility at an inappropriate concentration or structure. Calling it automatically prebiotic or antinutritional is therefore misleading. Its effect belongs to a defined ingredient, dose, process, life stage and complete diet.

Design a trial around a farm decision

Before changing feed, obtain a lot-specific specification covering moisture, crude protein, amino-acid profile, lipid and fatty-acid composition, ash, fibre or chitin, contaminants and stability. The insect species and rearing substrate should be traceable. European Union rules have allowed processed insect protein in aquaculture feed since 2017 under defined production and substrate conditions. Legal eligibility does not replace supplier assurance or complete-feed compliance.

A farm trial should compare isoenergetic diets that are as closely matched as possible for essential nutrients. Control and test populations need a duration relevant to the production stage. Core measures include feed intake, growth, feed-conversion ratio, mortality, size uniformity and water quality. Digestibility, body composition, intestinal condition and fillet quality may be added when they answer the decision being considered.

Observe the transition at feeding time. Reduced palatability can lower intake before a nutritional deficiency becomes visible. Conversely, growth maintained for several weeks does not establish equivalent lipid composition, robustness or full-cycle performance. Uneaten pellets, faecal appearance, dust and pellet buoyancy help separate formulation problems from feeding-system problems.

Circular potential is not a measured footprint

Insects can valorise selected co-products and reduce dependence on marine or crop proteins. Environmental performance nevertheless depends on the authorised substrate, electricity and heat used for rearing, drying and defatting, transport, and the ingredient that is genuinely displaced. A locally produced meal dried with a high energy demand is not automatically lower impact. Supplier-specific life-cycle information is stronger evidence than a generic sustainability claim.

Cost should be calculated per kilogram of fish produced, not per tonne of ingredient. Meal price, inclusion rate, feed conversion, losses, growth time and product value belong in the same calculation. The recent meta-analysis suggests broadly comparable economic performance, but only ten studies supported that component and regional prices can change quickly.

Use a staged, reversible decision

A robust transition has four steps: qualify the ingredient, reformulate on digestible nutrients, run a controlled trial, and decide against criteria fixed in advance. Stop rules should also be defined, including persistent intake reduction, poorer feed conversion, digestive lesions, mortality or unacceptable product composition.

Insect meals are neither a universal solution nor merely a novelty. They become useful when treated as variable, technical ingredients with auditable specifications. Vetofish can help farms define health and performance indicators, assess transition risks and interpret trial results alongside the nutritionist and feed manufacturer, without promising that one inclusion rate will suit every species or production system.