Finland produced 15.8 million kilograms of rainbow trout in 2024, accounting for 95% of the nation’s total food fish output. Despite this scale, feed quality inconsistencies—particularly poor water stability and pellet fragmentation—remain persistent challenges in Baltic Sea cage farming, where water currents accelerate nutrient leaching from substandard pellets. This case study follows a mid-sized trout producer in the Åland archipelago that replaced a decade-old pellet mill with Hongyang’s SZLH series ring die system. Within one production cycle, pellet durability index (PDI) rose from 91.2% to 97.8%, water stability extended from 28 to 45 minutes, and the farm reported a measurable improvement in feed conversion ratio. The results demonstrate that precision-engineered ring die technology can directly address cold-water aquaculture’s most demanding feed quality requirements.
Background: Finland’s Trout Aquaculture and the Feed Quality Imperative
Finland’s aquaculture sector operates under unique constraints. With over 200 fish farming enterprises managing 365 facilities across marine and freshwater sites, the industry faces year-round cold water temperatures that slow fish metabolism and extend production cycles. Rainbow trout (Oncorhynchus mykiss) dominates production, with the Åland Islands alone contributing nearly half of Finland’s marine-farmed output, according to Natural Resources Institute Finland (Luke) 2024 statistics.
NordAqua Oy (company name anonymized at client request), a mid-sized producer with six sea-cage sites in the Åland archipelago, produces approximately 800,000 kilograms of rainbow trout annually. The company operates its own feed mill to maintain control over ingredient sourcing and nutritional formulation—a strategic decision shared by several larger Finnish producers seeking to reduce reliance on imported feed from Alltech Fennoaqua, currently Finland’s only domestic aquafeed manufacturer.
“Feed represents over 50% of our operating cost. When pellet quality drops, two things happen simultaneously: fish waste feed, and uneaten pellets sink and degrade water quality beneath the cages.”
— Mr. Mikael Lindström, Production Manager, NordAqua Oy
The Baltic Sea’s brackish water and moderate currents mean that sinking feed pellets must retain structural integrity far longer than pellets used in still-water pond aquaculture.
The Challenge: Three Interlocking Feed Quality Problems
By early 2025, NordAqua’s aging pellet mill—a flat-die system installed in 2014—was generating three measurable problems that compounded each other:
Excessive Pellet Fines
The flat die had worn unevenly, producing pellets with inconsistent diameter and surface cracks. Sieve analysis showed 8–12% fines content (particles below 1.5 mm)—well above the 3% industry benchmark. These fines disintegrated on water contact within minutes, contributing to feed waste and localized eutrophication beneath cages.
Declining Water Stability
Pellets began disintegrating at 26–30 minutes in static water testing, compared to the 40-minute target required for Baltic Sea conditions. Fish feeding behavior in cold water (averaging 6–8°C in winter) is inherently slower, meaning pellets must remain intact long enough for fish to consume them at depth.
Rising Energy Costs
To compensate for deteriorating die condition, operators increased conditioning temperature and extended retention time, driving up steam consumption by an estimated 18%. The flat-die configuration also limited throughput to 1.2–1.5 t/h, creating production bottlenecks during the critical April–September growing season.
Hongyang Solution: SZLH Ring Die Pellet Mill with Custom Aquafeed Configuration
After evaluating suppliers from China and Europe, NordAqua selected the Hongyang SZLH ring die pellet mill based on three criteria: demonstrated aquafeed pellet durability data, availability of custom die configurations for sinking feed, and total cost of ownership including die service life projections.
Hongyang’s technical team specified the following configuration for NordAqua’s requirements:
The SZLH’s vertical ring die design provides two key advantages over flat-die systems for aquafeed production. First, the dual-roller compression mechanism distributes pressure more uniformly across the die face, reducing localized wear and producing pellets with consistent density. Second, the adjustable roller-die gap allows operators to fine-tune compression intensity for different feed formulations without changing the die itself.
Installation and commissioning were completed over a four-day window in March 2025, during a scheduled feed mill maintenance period. Hongyang’s remote technical support assisted NordAqua’s maintenance team with die alignment calibration and initial production parameter optimization.
Results: Measurable Improvements Across All Quality Metrics
NordAqua conducted a controlled comparison by producing identical feed formulations through the old flat-die system and the new SZLH ring die system. Results after 90 days of production:
Pellet Durability and Water Stability
The most significant improvement was in water stability—a critical metric for cold-water cage farming. Pellets produced by the HYPM system maintained structural integrity for 45 minutes in static water testing at 8°C, exceeding NordAqua’s internal benchmark of 40 minutes. This translated directly into reduced feed waste observed during feeding operations: the farm’s divers reported noticeably fewer uneaten pellets accumulating beneath cages.
Feed Conversion Ratio
While multiple variables influence FCR, NordAqua tracked a group of 50,000 fish fed exclusively with SZLH-produced pellets over a 120-day grow-out period from 200g to 850g average weight. The observed FCR of 1.08 represented an improvement from the previous cohort’s 1.14 using flat-die feed, saving an estimated 18 tons of feed per cycle.
At a feed cost of approximately €1,200 per ton, this translates to roughly €21,600 in direct savings per production cycle per cage group.
Production Efficiency
The 47% increase in throughput removed the summer bottleneck, allowing NordAqua to produce all required feed within regular operating hours rather than running extended shifts. The 19% reduction in specific energy consumption contributed approximately €4,800 in annual electricity savings based on Finnish industrial electricity rates.
Operational Observations
Mr. Lindström noted three practical advantages during the transition period:
“The die changeover is much simpler than we expected. With the old flat die, changing compression ratio meant swapping the entire die assembly, which took half a day. With the ring die, we can adjust the roller gap without disassembly—this saves us valuable time during formulation changes between starter and grower feeds.”
— Mr. Mikael Lindström, Production Manager, NordAqua Oy
The consistent pellet size distribution also improved the efficiency of NordAqua’s automated feeding barges, which rely on pneumatic blowers calibrated for uniform pellet diameter. Fewer clogging incidents were reported after the switch.
Conclusion
NordAqua’s experience illustrates a principle that extends beyond Finland’s aquaculture sector: feed pellet quality is not merely a production metric but a direct determinant of farm profitability and environmental performance. The Hongyang SZLH ring die pellet mill addressed the three interconnected problems—fines, water stability, and energy cost—through precision die engineering rather than process workarounds.
For cold-water aquaculture producers operating in exposed marine environments, investment in purpose-configured ring die technology delivers returns through multiple channels: reduced feed waste, lower energy consumption, and measurable FCR improvements. As the global aquaculture industry continues its shift toward intensive cage farming in challenging environments, the role of pellet quality as a competitive differentiator will only grow in importance.
Data sources: Natural Resources Institute Finland (Luke) Aquaculture 2024 statistics; NordAqua Oy production records (anonymized); Hongyang Feed Machinery technical specifications and commissioning reports.
Post time: Jun-16-2026
