What the Fish Leave Behind: Diet-Driven Loops in Recirculating Aquaculture Systems

Aquaculture is growing rapidly, but the availability of traditional feed ingredients like fish meal is limited. To meet demand, aquafeeds increasingly include alternative ingredients such as insect meal, seaweeds, and byproducts. These ingredients often contain more carbohydrates, which can be challenging to digest for carnivorous fish like European seabass and gilthead seabream. As a result, higher dietary carbohydrate levels can reduce fish growth and increase faecal waste production. While the effects on growth are well documented, the consequences for solid waste are often overlooked. This is particularly relevant in water-reuse systems such as recirculating aquaculture systems (RAS), where waste accumulation promotes microbial growth and deteriorates water quality, potentially compromising fish welfare.

This PhD project took a holistic approach to investigate how different carbohydrate sources influence faecal production, waste buildup, and microbial communities in both the fish and the aquaculture environment. The results provide guidance for selecting feed ingredients that not only support fish growth but also improve solid waste management and RAS functioning.