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Smoltification has always been a critical point in the salmon production cycle, but in recent years, it’s become something else entirely. It’s not just a biological transition anymore. It’s a business lever.
Farms around the world are transferring larger and larger smolt into the sea, trying to shorten ocean grow-out time and make better use of their limited permits. But with this shift has come a whole new set of questions. Are we asking fish to do something nature didn’t design them for? Can our systems actually support this shift? And most importantly: are we setting these fish up to thrive or just survive?
Let’s take a closer look at what’s happening.
Smoltification 101: What the Fish Are Actually Doing
Salmon don’t start life in the sea. They’re born in freshwater rivers and streams. Before they can handle saltwater, their bodies go through a complete transformation—a process called smoltification.
To survive the transition, salmon must reprogram how they handle salt. In freshwater, they’re constantly absorbing water and conserving salt. In seawater, they need to do the opposite: expel excess salt while holding onto water. This happens through changes in the gills, specifically in chloride cells and enzymes like Na⁺/K⁺-ATPase, which help pump salt out of the fish’s body.
Hormones like cortisol and growth hormone surge during this time, triggering both internal and external changes. Skin pigmentation shifts to a silvery sheen. Behavior changes too - smolts begin orienting downstream, ready to migrate.
In nature, smoltification is a flexible, seasonal process. But on farms, it’s a schedule.
Everyone Moves at Once: The Challenge of Uniform Readiness
Unlike wild populations, where fish migrate over a wide window, aquaculture operates on fixed timelines. Entire generations are transferred to sea cages in a single day. That means farmers need uniformity—every fish in the population needs to be physiologically ready for saltwater, or performance suffers.
To manage this, farmers use smoltification tests, often measuring chloride levels in the blood as a proxy for seawater readiness. Light control is also key: salmon use daylength cues to trigger smoltification, so many farms manipulate light cycles to initiate the transformation.
Other strategies include exposing fish to brackish water or feeding specialized diets to support the transition. When the timing is right, fish transfer successfully. When it’s off (even slightly) performance at sea declines.
The Industry’s Push for Bigger Smolt
In the last decade, the size of smolt has exploded. What used to be a 90–100g smolt is now pushing 200g in many operations, and some are going much further.
Bakkafrost is transferring 410g smolt in the Faroe Islands. In Scotland, 100% of their smolts are now over 200g. Grieg Seafood is targeting 1 kg smolt in Rogaland by 2025. The logic is clear: by growing fish longer on land, you can reduce time at sea by 6–8 months.
That shortens production cycles, increases turnover, and makes better use of ocean licenses. From a business perspective, it’s a smart move. From a biological perspective, it’s more complicated.
Bigger Fish, Bigger Complications
Larger smolt introduce new biological and operational challenges. First, light exposure becomes less reliable. Bigger fish block more light, and in deep tanks (especially in RAS systems) the fish near the bottom might not receive strong light cues. That makes uniform smoltification harder to achieve.
Then there’s the use of brackish water. Introducing saltwater into a freshwater RAS facility increases filtration demands and adds complexity. It’s not impossible but it’s harder to get right.
And perhaps most importantly, there’s concern around the speed of biological change. Pushing fish to grow quickly and transition faster may come with long-term health tradeoffs. Some researchers are questioning whether we’ve stretched the smoltification window too far.
Toolkits: Light, Water, and Feed
To meet these challenges, farms are using every tool available:
- Light management remains the primary trigger for initiating smoltification.
- Brackish water can help simulate natural transition conditions.
- Feed-based solutions are an emerging third pillar.
One of the more interesting developments in this space is Supersmolt, a specialized feed designed to support the physiological transition by delivering targeted amino acids, proteins, and trace elements. Its founder, Dr. Bill Harris, came from human kidney research before applying his findings to smolt biology—a reminder of just how complex this transition really is.
There’s no silver bullet. Most farms are finding success with a blended approach—optimizing light schedules, improving water systems, and experimenting with feed formulations. The common denominator?
Better timing, better data, and closer monitoring.
What the Data Tells Us - and What We’re Still Learning
At Manolin, we’re watching this space closely. Our data shows the shift toward larger smolt is accelerating but not always with consistent outcomes.
That tells us we’re still early in understanding how to optimize large smolt production. What works for one site might not translate directly to another. Environmental factors, water chemistry, genetics - they all play a role.
The key is learning faster. By aggregating operational data across farms and identifying what conditions lead to better post-transfer outcomes, we can start to decode the biological signals that predict smolt readiness, not just on paper, but in real-world performance.
Rethinking What Success Looks Like
Is bigger always better? Maybe. But only if you get it right.
As the industry keeps pushing the boundaries of land-based smolt production, the focus needs to stay on outcomes, not just targets. It’s not about hitting a weight. It’s about preparing fish that can thrive in the ocean.
Smoltification isn’t a checkbox. It’s a cascade of biological events that need to line up. And that means better planning, tighter coordination, and smarter tools.
We’re just beginning to see how data can guide those decisions. And that’s where we’re excited to help.
Want to know how your smolt production strategy compares? Let’s talk.