Johan Verreth has been working on the fate of nutrients and nutrient dynamics in different production systems of fish, e.g., in ponds, in recirculating aquaculture systems, and more lately also at the animal level. His main focus of interest is on the adaptive responses of the animal to its (rearing and/or living) environment, how the animal in the context of a particular production and farming system influences its environment and how the latter determines the performance and response of the fish.