Aquaculture waste production associated with antinutrient presence in common fish feed plant ingredients

The use of fish meal alternatives in aquafeeds is increasingly becoming a necessity due to declining fisheries stocks. Thus, the dietary formulations and their impacts remain a big challenge for the sustainability of the aquaculture sector. Plant ingredients have been successfully used as a sustainable alternative to fish meal for some aquaculture species. However, the presence of antinutritional factors in most of these ingredients interferes with feed acceptance and animal performance, causing impaired metabolism and digestibility. Besides the increased production costs, other concerns also arise from these impaired effects, such as waste production originating from nutrients not retained in biomass and released in the environment as faecal or non-faecal losses. In this review, we aim to address the impacts of the antinutrient factors, present in commonly used plant ingredients, on waste production, as it may lead to unwanted environmental changes. Reduction of waste outputs can be potentially achieved through the improvement of feed formulation, palatability, digestibility and nutrient retention. Indigestible plant components, such as non-starch polysaccharides present in high concentrations, increase faecal production and alter faecal properties; however, their impact depends highly on the rearing system i.e. open cages, flow-through or recirculating systems. As the study of faecal physical properties is a relatively new area, there is no agreement on the best parameter or method to use for predicting faeces behaviour in a commercial rearing system. Therefore, knowledge of the contribution of each antinutritional factor, and especially of non-starch polysaccharides, on faecal properties and waste production, and the levels that have the least environmental impact, is important and currently lacking.