How to Choose the Right Anchor Chains for Deep-Sea Fish Farms – A Procurement Guide
The losses from a single mooring failure can extend far beyond fish and equipment – they can lead to insurance voids, regulatory penalties, and years of reputational damage.
In February 2025, a major Norwegian salmon producer lost 27,000 salmon that had reached catch standard due to cage ring breakage caused by severe weather. In 2018, a Chilean producer lost 690,000 fish and was fined $7.5 million for failing to implement a recommended mooring system.
The additional cost of properly configuring a mooring system far outweighs the losses from a single fish escape.
1. Pricked Links vs. Nailless Links – Which is Better?
Based on our supply experience:
Norwegian fish farms tend to purchase pricked links because of the high winds and waves in Norwegian waters. Pricked links are over 30% stronger than nailless links and have better resistance to deformation.
Chilean fish farms, on the other hand, tend to purchase nailless links more often. Sheltered fjords, calm waters. Lighter, more economical.
Let sea conditions, not price, dictate.
2. Diameter and Grade – What Do You Really Need?
There's no one-size-fits-all answer. Diameter depends on water depth, wind direction, wave conditions, and seabed conditions.
In our experience: Aquaculture uses a wide range of chain diameters, from 16mm to 44mm, with 28mm to 36mm being the most common size for aquaculture mooring chains.
Most fish farms use U2 (AM2) grade chains. It strikes a good balance between strength and cost. U3 grade chains are more commonly used for marine anchor chains than in aquaculture. Recommending U3 grade chains for aquaculture is generally an overkill.
3. Surface Finish – Our Recommendations
Black paint is the most common choice – providing adequate protection at a lower cost.
Hot-dip galvanizing – We do not recommend this for chains with a diameter less than 20mm. High-temperature treatment reduces tensile strength. For larger diameter chains, galvanizing services are available upon special request.
Our recommendation: Most aquaculture chains are painted black. Galvanizing is only recommended for larger chains if the customer understands the trade-offs.
4. Why Actual Failures Matter
Scotland, 2020: Mooring lines far exceeding required strength still broke in a storm, resulting in the escape of 48,834 salmon. The problem was fatigue and dynamic loads, not static strength.
Scotland, 2018-2021: Three escape incidents occurred at the same exposure site within 27 months, resulting in the deaths of nearly 70,000 fish. The operator switched to 200-meter cages designed to withstand "once-in-two-hundred-year" storms.
Chile, 2018: 690,000 fish escaped, resulting in a $7.5 million fine. Cause: Failure to implement the recommended mooring system and neglect of wear and tear.
Lesson learned: For exposed locations, a “good enough” mooring system is far from sufficient. Worst-case scenarios should be considered in the design, not average-case scenarios.
5. Certification – Essential
Certification is mandatory, especially for Norwegian farms:
Insurance – Insurance companies require valid product certificates
Regulation – Authorities require the use of certified mooring systems to prevent vessels from breaking anchor
Compliance – Financing agreements often require the use of certified chains
SMEOCEAN provides chains certified by LR, ABS, DNV, BV, CCS, NK, KR, RMRS, RINA, and IRS.
6. Fittings – The Weakest Link
All fittings must match the chain’s grade and certification – for example, Kenter shackles, anchor shackles, swivel joints, end rings (E), and enlarged rings (EL). Mixing different certifications means your system documentation is incomplete – insurance companies will notice this.
Procurement List
Chain Diameter (16mm – 44mm, most commonly 28mm – 36mm)
Grade (U2 – Common standard for fish farms)
Type (Peged/Pegless – Depends on sea conditions)
Length (Customizable based on cage design and water depth)
Surface Treatment (Black paint, hot-dip galvanizing not recommended)
Certifications (LR / ABS / DNV / BV / CCS, etc.)
Accessories (Shackles, Swivels, Anchors,Mooring Plates,Ropes,Thimble,Mooring Ring)
Summary
Peged chains are suitable for exposed sea conditions, while pegless chains are suitable for sheltered sea conditions.
U2 is the standard grade – U3 is rarely used in aquaculture.
Chains with a diameter less than 20mm are recommended to be painted black – galvanizing reduces strength.
Design should consider the most severe sea conditions, not the average sea conditions.
All accessories must meet the chain specification grade requirements.
With 20 years of experience in aquaculture mooring, we supply chains, shackles, swivel joints, and accessories to farms in Norway, Chile, and elsewhere.
Coming next: In our next article, we'll break down how to select the right anchor type for different seabed conditions in aquaculture — from Stingray and Drag anchors to Dual Shank and Flipper Delta HHP anchors for deep-sea exposed sites.