Your Sushi is the Smart Work of Water Engineers

From Ocean to Omakase

I LOVE sushi, and it seems I’m not alone. The global sushi-grade seafood market was valued at roughly USD 10 billion in 2024, and is projected to reach USD 16 billion by 2034. From supermarket trays to high-end omakase counters, raw fish has gone mainstream.

I’d say these kids have taste. Source: x.com

But have you ever stopped mid-bite and wondered: where does this fish actually come from? And what does it take to make it safe enough to eat raw?

I did some diving and ended up somewhere unexpected: a water treatment plant.

The Fish Farming Boom and Its Baggage

To begin with, most fish we eat doesn’t come from ‘nature’ anymore. In 2022, aquaculture overtook wild capture in global production for the first time in history. The ocean simply can’t keep up with demand anymore.

This shift was necessary. With a growing global population and wild stocks under pressure - only 64.5% of all fishery stocks are fished sustainably - farm-raised fish fills a critical gap.

But traditional fish farming, the kind that uses open-water cages in the sea, comes with its own problems. Sea lice infestations that damage fish. Antibiotics used to control disease, which feels counterintuitive when many of us eat seafood for its health benefits. Excess nutrients from fish waste polluting the surrounding waters and degrading local ecosystems.

Fish farms are facing backlash from local communities. Source:  The Scotsman. 

Then what if we cut the operation off from the open environment and try to keep everything under control?

Landing Aquaculture

You might have seen fish tanks in Cantonese restaurants or supermarkets in Chinatown. Indoor fish farms aren’t so different in principle (water, tanks, pipes, pumps), but the devil is in the details. Or rather, the tech.

I had a go at ‘aquaculture’ when I found two goldfish in the street. Believe it or not, it’s not been easy to keep them alive.

Recirculating Aquaculture Systems (RAS) are essentially indoor fish farms. Think of it as a water treatment plant whose job is to keep fish alive and thriving. These systems recirculate up to 99% of their water through a treatment loop that filters out waste, converts toxic ammonia into harmless compounds, manages dissolved oxygen and CO2, and controls temperature precisely.

While it does consume a lot of energy compared to open water aquaculture, the advantages are significant. No sea lice. No antibiotics leaking into the ocean. No dependence on weather or ocean conditions. You can build a RAS facility anywhere. A landlocked city. In the desert or high up on the mountain.

Perhaps most importantly for our sushi story: the controlled, clean-water environment of RAS is a natural match for sushi-grade fish. When you’re producing fish intended for raw consumption, keeping the fish alive is just the starting point. You have to make sure there are no parasites, and the flavour is spot on — yes, water quality can affect the taste.

Water Quality: No Margin for Mistakes

In a RAS facility, the water treatment system is the lifeline of the entire business. A small chemical imbalance - a pH shift, an ammonia spike, a temperature fluctuation - can wipe out the entire stock overnight.

To understand the stakes, consider the ammonia challenge. Fish excrete ammonia through their gills. In a high-density tank, ammonia can reach lethal levels within hours. Biological filters convert this ammonia into less toxic compounds, but the process is sensitive to pH. A tiny pH increase can dramatically shift the balance between harmless and toxic forms of ammonia.

A closed recirculating aquaculture system in Japan. Source: FRD Japan.

.The margin for error is razor-thin. Atlantic Sapphire, the world’s largest land-based salmon farm in Miami, learned this the hard way. In 2021, the company suffered mass fish die-offs due to failures in gas handling. Further temperature control issues in 2023 during Florida’s intense summer heat led to additional losses.

Getting the water right, on the other hand, pays off. The Kingfish Company, based in the Netherlands, farms sashimi-grade Yellowtail Kingfish entirely on land. Without antibiotics or vaccines, they’ve achieved zero mass mortalities since the start of operations. They’re now breeding fourth-generation fish specifically adapted to RAS conditions, powered by 100% renewable energy.

What It Means for Water Professionals

When talking about wastewater treatment, you probably picture someone working in very specific locations, such as municipal treatment, utilities, maybe industrial processing. But the core competencies that make a good water professional are remarkably transferable. RAS is one of the most compelling examples.

The science doesn’t change. Biological filtration, chemical dosing, sludge management, real-time monitoring… These processes work the same way whether you’re treating sewage, keeping fish alive, recycling water in a brewery, or managing cooling loops in a data centre. What changes is the context.

The global RAS market was valued over USD 5 billion in 2025, and is growing fast. The talent pipeline needs to keep up.

Here are the skill areas that RAS facilities are actively looking for.

Process engineering and water chemistry. Understanding how biological filtration works, how dissolved gases behave, how pH interacts with ammonia toxicity. If you’ve worked in municipal wastewater treatment, you already speak this language.

Real-time monitoring, automation, and data analysis. RAS facilities run on 24/7 sensor networks and increasingly AI-driven predictive tools. Machine learning models are already achieving up to 99% accuracy in classifying fish health from sensor data alone. If you’ve worked with smart water networks, SCADA systems, or IoT platforms, this is a lateral move.

Mechanical and electrical maintenance. Pumps, valves, filtration units, UV systems — all running non-stop in potentially corrosive environments. This is one of the most accessible entry points for people coming from utilities, manufacturing, or HVAC.

Resource recovery and circular economy. RAS produces concentrated waste streams rich in phosphorus and nitrogen. Skills in nutrient recovery, anaerobic digestion, and biosolids management are increasingly sought after — and they’re portable across the entire water sector.

What is new in RAS is the biological dimension. You’ll need to learn about fish health, biosecurity, and feed management. But that could be an exciting stretch, not a career restart.

Where to start. Several organisations offer structured pathways into this space: CIWEM’s Chartership route for professional recognition, the Aquacultural Engineering Society’s RAS Certificate Course for technical foundations, UHI Shetland’s apprenticeships for hands-on training, and Lantra’s career profiles for getting a glimpse of a day in the life at aquaculture work.

Final Random Bits

One thing I like about omakase is I get to interact with the chefs or sous chefs. Normally, I’d ask where the fish is sourced, how they come up with the recipe, certain urban myths - such as whether all “wasabi” is really wasabi. I guess next time, I can also quiz them about RAS, water quality and flavours. Hopefully I won’t get kicked out or blacklisted.

Source: Pinterest.