Prebiotic and probiotic applications in fish and crustaceans

An array of functional feed additives are now routinely used in aquafeeds. Amongst the most widely used, and comprehensively studied, are prebiotics and probiotics. They are applied with the aim of improving the host microbiome, primarily within the gastrointestinal tract, with subsequent benefits for the host organism. The intestinal microbiota is a complex community comprising bacteria, yeast, archaeans, protists and viral particles. These communities are intimately linked to host health, digestive function and metabolism. Scientific studies have demonstrated that a number of prebiotic compounds (inulin and various oligosaccharides) and probiotic species (mainly, but not exclusively, Bacillus spp. and lactic acid bacteria) can have positive impacts on the microbial communities of fish and crustaceans, which subsequently improves host growth performance, immunity, intestinal health and survival (under challenged and nonchallenged conditions). Although the mechanisms of action that underpin such benefits are becoming better defined, there is still much to learn. Consistency of outcomes is another topic that warrants further attention since the composition and activity of the microbiomes of fishes and crustaceans are influenced by multiple biotic and abiotic factors (e.g., water quality, temperature, diet, genetics etc) which are highly variable among different farm operations. As such, the reproducibility of beneficial outcomes is not guaranteed even when using the same products, doses and aquatic species. Therefore, there is no one-size-fits-all approach; the product used, and the optimal dosage, need to be carefully considered in the context of the aquatic species, life stage, rearing system, rearing conditions, and dietary raw materials used.