Aquaculture is the world's fastest-growing agri-tech sector. But it’s not without challenges. Sustainability, disease control, limited expansion space, and freshwater availability are pressing concerns. While recirculating aquaculture systems (RAS) have offered solutions, their water monitoring systems lack real-time sensors to quantify highly toxic compounds like ammonia, nitrite, and nitrate. These compounds can accumulate in closed systems, posing a severe threat and leading to sudden mass mortality in fish populations. In this context, the EU-funded iTOP-RAS project aims to revolutionise aquaculture. Their portable nitrite biosensor, the NO2Aqua, delivers accurate real-time results. Additionally, the NOxAqua and NOxAquaPlus products offer comprehensive monitoring capabilities and automation for the three N-nutrients, reducing mortality risks and propelling the industry towards Aquaculture 4.0.