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

A study published October 2, 2026, in Veterinary Sciences takes a closer look at one of aquaculture nutrition’s central questions: how much fishmeal can be replaced before performance starts to slip. In red tilapia, researchers found that replacing commercial fishmeal with a blend of Azolla microphylla meal and soybean meal led to progressively poorer growth and feed conversion as inclusion rose from 25% to 75%. At the same time, moderate replacement preserved fillet amino acid quality better than the highest inclusion level, and the paper adds exploratory observations on intestinal microbiota and post-challenge health responses. (mdpi.com)

The backdrop is a broad industry push to reduce dependence on fishmeal, which remains a costly and finite ingredient even in species like tilapia that already use less of it than many carnivorous fish. Azolla has long attracted attention as a low-cost aquatic plant protein, and prior work has suggested it can be included at modest levels in tilapia diets. Reviews of the literature, however, consistently describe a ceiling: azolla can help as a partial replacement, but higher inclusion often brings fiber, antinutritional factors, and amino acid limitations that can depress performance unless the diet is carefully balanced. (onlinelibrary.wiley.com)

That context matters for interpreting the new paper. The authors formulated isonitrogenous and isoenergetic diets with 0%, 25%, 50%, and 75% fishmeal replacement, but soybean meal rose alongside A. microphylla meal. In other words, this was not a clean azolla-only substitution study. According to the abstract and article page, weight gain, average daily gain, and specific growth rate fell as fishmeal replacement increased, while feed conversion ratio increased. Serum biochemistry shifted as well, with AST rising and ALP falling at elevated replacement levels. Fillet total essential amino acids were significantly reduced only in the 75% replacement group, suggesting moderate substitution may be more workable if fillet nutritional profile is part of the goal. The intestinal microbiota component was explicitly exploratory, using pooled composite samples that do not support statistical inference. (mdpi.com)

The findings line up with a parallel 2026 paper in Aquaculture Research examining A. microphylla replacement in red tilapia under Aeromonas hydrophila challenge. That study reported that 50% and 75% substitution significantly reduced growth, while 25% did not impair growth relative to control. It also found that higher azolla inclusion, especially 50%, enhanced hepatic immune and antioxidant responses after challenge, underscoring a potential growth-immunity trade-off rather than a simple success-or-failure story. (onlinelibrary.wiley.com)

More broadly, prior tilapia studies and reviews point in the same direction: modest azolla inclusion can be feasible, but performance tends to deteriorate as replacement climbs. A 2024 PubMed-indexed study in red tilapia fingerlings found the best specific growth at 20% azolla inclusion under some salinity conditions, while 60% performed worst. A 2023 review concluded that optimal inclusion remains species- and formulation-dependent, and called for more work on compatibility with other feed ingredients. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For veterinary professionals working in aquaculture, this is less a story about whether azolla “works” and more a reminder that alternative protein strategies have multiple endpoints. Growth, feed efficiency, serum chemistry, muscle amino acid composition, gut ecology, and disease resilience may not move in the same direction. If a farm or feed program is optimizing for fastest growth, the new data support caution beyond 25% replacement. If the goal includes reducing fishmeal dependence while maintaining fillet quality, the study suggests 50% may be a more realistic upper boundary than 75%, though even that comes with performance costs. And because soybean meal increased alongside azolla, nutritionists should be careful not to over-attribute the outcomes to azolla itself. (mdpi.com)

The microbiota angle is also worth watching, even if this paper’s dataset is preliminary. Fish gut microbiome research increasingly suggests diet composition can influence intestinal community structure, nutrient metabolism, and immune function, but robust conclusions require adequate replication and statistical power. The authors’ decision to label their microbiota findings as exploratory is important, and it sets a sensible boundary for how far practitioners should take the results today. (mdpi.com)

What to watch: The next step will likely be more targeted formulation studies that separate azolla’s direct effects from soybean co-replacement, test amino acid balancing or enzyme support, and evaluate whether moderate inclusion can deliver sustainability gains without unacceptable losses in growth or fillet quality under commercial conditions. (mdpi.com)