Red tilapia study maps trade-offs in azolla-based fishmeal replacement blend

A study published on 2 October 2026 in Veterinary Sciences has quantified the performance trade-offs in red tilapia when commercial fishmeal is replaced with a blend of Azolla microphylla meal and soybean meal, finding that growth and feed efficiency declined progressively as fishmeal replacement rose from 25% to 75%.

Researchers fed red tilapia isonitrogenous and isoenergetic diets at four fishmeal replacement levels — 0%, 25%, 50%, and 75% — over a 60-day trial. According to the study, weight gain, average daily gain, and specific growth rate all fell as replacement increased, while feed conversion ratio worsened. Serum biochemistry also shifted, with AST rising and ALP falling at elevated replacement levels.

Fillet amino acid quality showed a more nuanced pattern. The study found that fillet total essential amino acids were significantly reduced only in the 75% replacement group, indicating that moderate substitution may be more workable for producers prioritising fillet nutritional profile. The authors also included an intestinal microbiota component, but explicitly labelled those findings as exploratory, noting that pooled composite samples do not support statistical inference.

A key methodological caveat accompanies the results: because soybean meal increased alongside A. microphylla meal in the formulations, the paper's authors note the outcomes reflect the combined fishmeal replacement strategy rather than the effect of azolla alone. Nutritionists are therefore cautioned against attributing observed changes solely to azolla.

The new paper is accompanied by a parallel 2026 study in Aquaculture Research that examined A. microphylla replacement in red tilapia under an Aeromonas hydrophila challenge. That study reported that 50% and 75% substitution significantly reduced growth, while 25% did not impair growth relative to controls. It also found that higher azolla inclusion — particularly at 50% — enhanced hepatic immune and antioxidant responses after the bacterial challenge, pointing to a potential growth-immunity trade-off rather than a straightforward outcome.

The findings sit within a broader body of literature on azolla as an aquafeed ingredient. A 2024 PubMed-indexed study in red tilapia fingerlings found the best specific growth at 20% azolla inclusion under certain salinity conditions, while 60% inclusion performed worst. A 2023 review concluded that optimal inclusion levels remain species- and formulation-dependent and called for further work on compatibility with other feed ingredients.

For aquaculture nutritionists, the collective evidence frames the decision as a multi-objective optimisation. Up to 25% replacement appeared to preserve growth in the new trial, while up to 50% preserved fillet nutritional quality better than 75%. Higher inclusion may carry immune-related benefits under pathogen pressure, according to the parallel challenge study, but those potential benefits come at a measurable cost to growth performance and feed efficiency.

The authors' decision to use an exploratory label for the microbiota data is significant, as fish gut microbiome research increasingly links diet composition to intestinal community structure and immune function, but robust conclusions require adequate replication and statistical power that the current dataset does not provide.

Researchers and industry observers expect follow-up work to focus on separating azolla's direct effects from those of the co-varying soybean meal, testing amino acid balancing or enzyme supplementation, and evaluating whether moderate azolla inclusion can deliver sustainability gains without unacceptable losses in growth or fillet quality under commercial conditions.