Different Materials In Cage Net
- Polyamide (PA), or nylon
- Sinks (density = 1.14)
- Very resistant to breaking
- Very resistant to abrasion
- High elongation (stretch)
- Excellent flexibility
- High capacity for absorbing different resins
Nylon is the most commonly used fibre in cage aquaculture. Netting for cages, mooring lines and lines used for attaching the net to the collar are mostly made with nylon.
Nylon has poor resistance to UV light and will deteriorate, thus all the equipment made with this fibre must be properly stored away from direct sunlight. The longer nylon nets or ropes are exposed to UV light, the greater the decrease in breaking load and overall strength, resulting in a higher risk of structural breakages.
Nylon is highly elastic (23 percent at breaking load), which can increase the length of each component after a working period of few months by about 10 percent. Therefore, a nylon mooring system will need to be tensioned again a few months after it has been deployed. Nylon net cages will increase in depth by 5–10 percent owing to the elongation of ropes and netting subjected to loads from biofouling or the sinkers on the net.
Nylon fibres can also shrink, causing problems in netting. After several net-washing operations, it is possible that the horizontal dimensions of the cage can be reduced by 3–5 percent. In the net assembly, consideration must always be made for this factor and extra netting built into the design to allow for this phenomenon.
- Polyethylene (PE)
- Floats (density = 0.94–0.96)
- Good resistant to abrasion
- Good elasticity.
Polyethylene and high density polyethylene nets are often used as anti-bird/anti-predator nets due to their light weight and resistance to abrasion. Braided or twisted knotted nets are being used in salmon growout in locations where nets treated with antifouling are banned and frequent on site net cleaning is required.
- Polyester (PES)
- Sinks (density = 1.38)
- Highly resistant to breaking
- Good flexibility
- Low elongation
- Highly resistant to UV exposure
Polyester has very good resistance to UV light, so it is commonly used for nets that have to be exposed to the sunlight, such as bird nets mounted above the cages, and anti-abrasion net panels around the waterline of the cage.
Compared with nylon, PES is about 20–25 percent heavier (to achieve the same breaking load), but PES has the advantage of not absorbing water, whereas nylon can absorb up to 10 percent of water.
The heavier characteristics of PES can be of value in nets exposed to strong currents because the low elongation of the material ensures that the net will maintain its shape relatively well.
- Polypropylene (PP)
- Floats (density = 0.92)
- Resistant to breaking
- Highly resistant to abrasion
Polypropylene netting is not commonly used in cage net manufacturing, but is instead often used for predator nets (commonly for bird protection nets). Polypropylene nets with a large mesh size and large twine thickness are also used as spat collectors in mussel culture, because the buoyancy of the fibre contrasts the weight of the mussels that attach to the net.