Microalgae additives may help seabream handle plant-based diets: full analysis

A growing body of aquaculture nutrition research suggests microalgae-based nutraceuticals could help soften the downside of plant protein-heavy feeds in gilthead seabream. In the latest cluster of studies, researchers found that juvenile fish fed a diet with sharply reduced fishmeal and fish oil had poorer growth, metabolic performance, and welfare indicators, while diets supplemented with specific microalgae-derived additives partly improved those outcomes, especially measures tied to intestinal integrity and stress physiology. (sciencedirect.com)

The backdrop is familiar across aquaculture: fishmeal and fish oil are expensive, finite inputs, so feed formulators have spent years increasing plant-based ingredients. But high plant inclusion can come with anti-nutritional factors such as saponins, glucosinolates, phytates, antivitamins, and trypsin inhibitors, all of which may impair digestion, growth, and gut health, particularly in carnivorous species like seabream. The research team framed its work around that tension, asking whether functional additives could preserve performance while supporting a broader shift toward more sustainable feeds. (rodin.uca.es)

In the 2025 Aquaculture paper that provides important context for the Animals study topic, investigators tested four diets for 90 days in juvenile seabream starting at about 28.4 g body weight: a commercial-style control diet with 20% fishmeal and 9% fish oil, a plant-forward diet with 5% fishmeal and 5% fish oil, and that same plant-based diet supplemented with 1% LB-IMMUNOboost or 1% LB-LIVERprotect. The unsupplemented plant-based diet reduced growth performance, metabolic rates, and overall welfare. LB-IMMUNOboost partially reversed those effects, improving growth-related measures, plasma cortisol, and intestinal barrier markers including epithelial resistance and apparent permeability. Histology also showed diet-related intestinal changes and adipocyte accumulation around the exocrine intrahepatic pancreas in fish on plant-based diets. (sciencedirect.com)

The additives themselves are worth noting. According to the paper, LB-IMMUNOboost contains enzymatically hydrolyzed yeast cell wall plus a hydrolyzed microalgae blend including Chlorella and Nannochloropsis, while LB-LIVERprotect combines artichoke and grape marc polyphenolic extracts, choline salts, and hydrolyzed microalgae including Arthrospira and Nannochloropsis. A related 2026 Scientific Reports study from the same line of work found that low dietary inclusion of comparable microalgae-derived nutraceuticals increased total alkaline protease, chymotrypsin, leucine aminopeptidase, and alkaline phosphatase activity, supporting the idea that these products may improve digestive function and nutrient absorption in juvenile seabream. (rodin.uca.es)

Industry and research interest in this area has been building for several years. Earlier studies in gilthead seabream have linked low-level microalgae supplementation with improved feed efficiency, shifts in muscle lipid composition, better intestinal physiology, and, in some cases, longer-term effects on muscle growth patterns. The newer work doesn’t stand alone; it fits into a broader effort to use algae-derived ingredients not as bulk protein replacements, but as precision functional additives that may help fish tolerate more aggressive reformulation of aquafeeds. That distinction is important because the authors also note that economic and technical barriers still limit microalgae’s use as a large-scale replacement for fishmeal or fish oil. (nature.com)

Why it matters: For veterinary professionals in aquaculture, these findings are most relevant as a gut health and welfare story, not just a feed ingredient story. If plant-based formulations are going to keep expanding, then managing downstream effects on intestinal integrity, nutrient utilization, stress signaling, and performance becomes a clinical and production issue. The reported cortisol patterns are especially notable: the plant-based negative control group showed elevated cortisol consistent with chronic nutritional stress, while the LB-IMMUNOboost group moved closer to the commercial-diet control. That suggests some functional additives may help reduce physiological strain even when marine ingredients are substantially reduced. (rodin.uca.es)

There are still limits. The researchers describe the work as preliminary, and the benefits were partial, not complete. The most favorable effects were additive-specific, and the studies were conducted under controlled experimental conditions rather than full commercial farm settings. Even the authors say further studies are needed to clarify the products’ full potential, mechanism of action, and value under routine production pressures. (sciencedirect.com)

What to watch: The next questions are whether these benefits translate into better health and production outcomes at scale, how consistent the response is across life stages and species, and whether the economics work for feed manufacturers and producers. One paper in this research stream estimated that LB-IMMUNOboost could reduce feed costs versus an unsupplemented extreme plant-based diet by as much as €380 per metric ton of fish produced, but that kind of modeled advantage will need real-world validation. (rodin.uca.es)