Predator-free fish cultivation with knotless UHMWPE nets
Fish cultivation or aquaculture is a rapidly growing industry in Indonesia. Until 2016, FAO recorded that Indonesia could produce 5 tons of fish (excluding seaweed), which included various saltwater, freshwater, or brackish water fish species.
Aquaculture in HDPE floating marine cages is one of the most consistent methods to produce fish in large quantity. Wave resistant and environmentally friendly HDPE floating marine cage is the key for a sustainable and profitable aquaculture. However, in addition to using HDPE floating marine cages, it is equally important to use the right nets on the cages.
The General Manager of PT Gani Arta Dwitunggal, Andi Jayaprawira, stated that aquaculture cannot use the same nets as the fishing nets. Fishing nets have large and very rough knots which pose a high risk of wounding the fish.
The wounds can result in scratch defects on the fish’ scales, and in infections which increase mortality rate. Hence, the use of knotted nets is highly not recommended.
Therefore, Andi stated that fish cultivators are highly recommended to use knotless nets with smooth surface. Knotless nets will not wound the fish’ scales, thus decreasing mortality rate and increasing the fish’ selling value due to their perfect scales condition.
In the market, knotless nets are available in various materials such as HDPE, metal and UHMWPE. The first category, the knotless HDPE net, has light and flexible construction, hence it is easy to operate, and with affordable price.
This net is widely available in the market and has been manufactured domestically by a company which supplies facilities and infrastructures for fish cultivation, PT Gani Arta Dwitunggal, with the brand Aquatec. The second category, metal net, has heavy and rigid construction, but is commonly used to deter predators.
The third category, the knotless UHMWPE net, is a new aquaculture innovation that is gaining popularity. But what is UHMWPE? UHMWPE stands for Ultra High Molecular Weight Polyethylene, which is a material with tensile strength stronger than steel, but lighter and more flexible. Due to its strength, UHMWPE material has been used to certain heavy industries as a substitute for steel chain and alternating steel.
Knotless UHMWPE net is an aquaculture net made from the said material, hence the strength of each net pillar is equal to steel wire of the same size. Because of this, a single knotless UHMWPE net spread is extremely strong and can withstand up to several tons of loads.
Aside from its tensile strength, Andi explained, UHMWPE is also hard to break and resistant to corrosion. The knotless UHMWPE nets are used to protect fish from saltwater and freshwater predators, and have been proven to withstand attacks from various predators such as barracudas, puffer fish, pomfrets, crabs, turtles, and other predators, even sharks of certain sizes. With this net, fish cultivation is safe until harvest time even if the floating marine cage is installed in areas with high predator population.
Being a maritime country, Indonesia does have high ocean predator population. If left unanticipated, this can jeopardize mariculture businesses. This would be unfortunate because the mariculture economy potential is very high due to its higher commodity value compared to that of freshwater fish. Therefore, this anti-predator cultivation net is really needed.
In regards to its durability in withstanding predators, UHMWPE cultivation net is comparable to nets with metal material. In terms of price, UHMWPE cultivation net has far more economical price compared to metal nets. Hence it is a better and more affordable choice for fish cultivators.
In addition, unlike metal nets, the light and flexible UHMWPE cultivation net makes it easy to install in the field and to lift to the surface during maintenance and harvest.
“The knotless UHMWPE cultivation nets from PT Gani Arta Dwitunggal have been used by several companies in Bali to rear white snappers and to fend of predators such as barracudas and sharks,” Andi said.
Andi stated that during their usage period, not a single net was torn, even after being bitten by a medium sized shark. The smooth knotless surface results in white snappers with perfect scales, and low mortality rate and high survival rate. Those white snappers are then exported to Australia and United States.
The price of knotless UHMWPE cultivation nets are usually 2-2.5 times higher than the knotless HDPE cultivation nets, with up to 10-years lifetime in the ocean and up to 15 years in freshwater with the proper maintenance.
Judging by its benefits in fending off predators, its ease of usage, and its long lifetime, the knotless UHMWPE cultivation net is predicted to occupy a unique market in the aquaculture industry in Indonesia as the best solution for predator-free aquaculture.