A fishing net is often judged by what people can touch.
Buyers feel the twine, examine the knots, compare the color, and ask whether the material is thick enough. These details are important, but one of the most influential features of a fishing net is actually the empty space between its strands.
That empty space forms an invisible highway for water.
Through thousands of mesh openings, fresh water enters an aquaculture cage, oxygen reaches the fish, heat moves through the enclosure, and waste products travel away. When those openings become too small, distorted, or covered with biological growth, the underwater environment can change dramatically.
A fishing net does not only contain fish. It also controls how water moves around them.
Every square meter of netting contains two basic components:
Solid twine;
Open mesh area.
The twine provides strength and containment. The open area allows water to pass through.
A successful net must balance both.
If the twine is too thin for the working conditions, the net may suffer from abrasion, cutting, fatigue, or breakage. If the twine is unnecessarily thick, it occupies more space and creates additional resistance to the current.
The same relationship applies to mesh size.
Small openings can retain juvenile fish, shrimp, or other small aquatic animals. However, they also reduce the amount of open space available for water exchange.
Large openings improve water passage and reduce drag, but they may allow smaller stock to escape.
The correct fishing net is therefore not simply the strongest or finest product. It is the product that provides suitable containment while preserving enough open area for the environment.
Open area is the percentage of a net panel that is not occupied by twine.
Imagine looking directly at a stretched net.
Some of the visible surface is formed by strands and knots. The remaining part consists of holes through which water can pass.
A net with thin twine and large meshes usually has a high open-area percentage. A net with thick twine and small meshes generally has a lower one.
Two nets may have the same listed mesh size but different open areas because their twine diameters are not identical.
For example, a fine twine leaves more room inside each opening. A heavier twine occupies more of the same mesh space.
This difference can affect:
Water velocity through the cage;
Oxygen delivery;
Waste removal;
Temperature distribution;
Current pressure;
Fouling sensitivity;
Fish behavior;
Structural loading.
Open area is especially important in aquaculture because the net forms part of the animals’ living environment.
A fish cage can be compared to a room with mesh windows.
The fish consume oxygen and release carbon dioxide, waste, and uneaten feed. Fresh surrounding water must enter the enclosure while used water moves away.
This continuous replacement is called water exchange.
In a well-positioned and properly designed cage, natural currents provide much of this movement. Water enters through the upstream panel, passes through the stock area, and exits from the opposite side.
The netting influences how easily this process occurs.
A clean net with an appropriate open area allows water to pass relatively freely. A dense or fouled net behaves more like a partially closed curtain.
The flow slows down, changes direction, or travels around the cage rather than through it.
From the surface, the cage may still appear normal. Underwater, however, the internal environment may be receiving less fresh water than expected.
Fish obtain dissolved oxygen from water through their gills.
The amount of oxygen available depends on several factors, including water temperature, stocking density, fish activity, algae, feeding intensity, and current conditions.
During feeding, fish become more active and usually consume more oxygen. Warm water may hold less dissolved oxygen than cooler water. At night, certain biological processes can also reduce oxygen availability.
Good water exchange helps replace oxygen used inside the cage.
A blocked or heavily fouled net can restrict this replacement. The risk becomes greater when many fish are concentrated in a limited volume.
Low oxygen may cause fish to gather near the surface, reduce feeding, move toward areas with stronger flow, or show signs of stress.
For this reason, net cleaning and mesh selection are not merely maintenance decisions. They can influence animal welfare and production performance.
Fish cages do not have mechanical floors that automatically remove waste.
Feed particles, organic matter, feces, mucus, and other materials move through the water and gradually leave the enclosure.
Sufficient circulation helps transport these substances away from the immediate farming area.
When water movement becomes weak, waste can remain suspended inside the cage for longer periods. Some particles settle below the farming site, while others collect against the mesh or circulate around the stock.
Poor exchange can also create uneven conditions.
One part of the cage may receive better water than another. Fish may begin gathering near the sections with higher oxygen or stronger circulation.
This crowding can further reduce the effective swimming space and increase contact between animals.
A correctly selected net supports a healthier balance by allowing water and suspended material to move through the structure.
People often assume that water exchange depends only on mesh size.
In reality, several net characteristics work together.
Thicker twine occupies more of the net panel and increases drag. It may offer greater resistance to wear, but it also reduces open area.
Knots create thicker intersections than the surrounding strands. In fine-mesh knotted nets, a large number of knots can contribute noticeably to the solid surface.
A fully opened mesh allows more direct water passage. A narrow, stretched diamond mesh has a smaller effective opening when viewed from the current direction.
The direction in which the net is mounted affects how the meshes open under tension. Incorrect orientation may cause the panel to narrow or distort.
When a current pushes the net downstream, the panel changes angle. Water no longer approaches every mesh directly, which can alter flow through the cage.
Algae, shellfish, sediment, and other organisms thicken the strands and cover the openings.
A professional net assessment should therefore examine the complete structure rather than relying on one specification.
A new fishing net may begin its working life with clean, clear openings.
Soon after installation, microscopic organisms attach to the surface. This first layer creates suitable conditions for larger forms of life.
Algae grow along the twines. Barnacles, hydroids, mussels, and other organisms may follow, depending on the location.
The process is called biofouling.
At first, the growth may appear harmless. Over time, it can transform the net.
The twine becomes thicker. Mesh openings become narrower. The net becomes heavier and rougher. Water resistance rises.
A mesh that originally allowed easy circulation may eventually behave like a much denser material.
The resulting drag pushes the cage farther downstream and transfers additional force to ropes, seams, frames, anchors, and connection points.
This is why operators should not wait until the mesh appears completely blocked before cleaning it.
By that stage, the cage may already be experiencing reduced water exchange and increased structural pressure.
Water movement is essential, but stronger current is not always better.
Moderate flow brings oxygen and carries waste away. Extremely strong flow can deform the cage, exhaust fish, increase drag, and overload the support system.
Fish must use energy to maintain their position in moving water. A species adapted to calm ponds may struggle in fast coastal currents.
The net changes the current as well.
Water slows when passing through the mesh. Turbulence forms behind the twines, and different parts of the cage may experience different flow patterns.
When several cages are positioned close together, the upstream cages can influence the water reaching those behind them.
Farm layout, spacing, cage orientation, and local current direction should therefore be considered together with net specifications.
A suitable mesh helps manage water movement, but it cannot correct a poorly selected farming location.
Juvenile fish require smaller mesh openings to prevent escape.
This creates a difficult engineering balance.
The net must be fine enough to retain the stock, but open enough to provide adequate circulation. Fine-mesh nursery cages may therefore require:
Lower stocking density;
More frequent cleaning;
Careful site selection;
Stronger inspection routines;
Better oxygen monitoring;
Suitable support structures.
As the fish grow, operators may transfer them into cages with larger mesh.
The larger openings improve water exchange and reduce drag while still retaining the larger animals.
Using one mesh size for every growth stage may be convenient, but it is not always efficient.
Uneven mesh openings create several problems.
A mesh that is too large may permit escape. A mesh that is too small may reduce local water passage.
Irregular knots can also create uneven tension. Some parts of the panel may stretch more than others, causing distortion during installation.
Consistent production helps the net distribute force and maintain a more predictable open area.
Important manufacturing controls include:
Uniform twine diameter;
Stable strand twisting;
Consistent knot formation;
Accurate mesh spacing;
Controlled heat setting;
Even panel dimensions;
Reliable border attachment.
A net does not need to be perfectly identical at every microscopic point, but major variations can affect its practical performance.
Fishing nets are commonly rolled, folded, compressed, or bundled for transport.
When first unpacked, the meshes may appear smaller or irregular because the material has been stored under pressure.
The panel needs time to relax and should be opened in the correct direction.
Measurement should also use a defined amount of tension.
Pulling too softly can leave the mesh partly closed. Pulling too hard can exaggerate the opening and distort the panel.
For knotted diamond netting, buyers and suppliers must clearly confirm whether the stated dimension refers to knot-to-knot distance, bar length, stretched mesh, or another method.
Clear measurement standards prevent disputes and help ensure that the final net provides the intended containment and water flow.
Cleaning restores open area, but aggressive cleaning can damage the structure.
High-pressure washing, hard scraping, rough handling, or unsuitable machinery may cut fibers, loosen knots, damage coatings, or weaken seams.
The cleaning method should match:
Net material;
Twine construction;
Knot type;
Fouling species;
Coating;
Age of the net;
Degree of contamination.
In some operations, nets are removed, washed, dried, inspected, and rotated. In others, underwater cleaning equipment is used.
Whatever the method, operators should check the panel after cleaning.
A clean net is not automatically a safe net. Damage hidden beneath the fouling may become visible only after the biological material is removed.
Water pressure acts across the entire net panel, but the force eventually reaches the border.
The border rope, sewing twine, corners, and attachment points connect the flexible mesh to the supporting structure.
If the panel has low open area or heavy fouling, the border must carry greater load.
Weak stitching or excessive attachment spacing can create concentrated stress. One connection may begin to cut into the mesh while nearby sections remain relatively loose.
A reliable design distributes the load through:
Suitable border rope;
Consistent sewing;
Reinforced corners;
Correct attachment spacing;
Protected contact surfaces;
Balanced installation tension.
The main panel and its border should always be evaluated as one system.
Operators can take several practical steps to support better flow:
Select mesh size according to fish size and environmental conditions;
Avoid unnecessarily thick twine;
Install the net in the correct orientation;
Maintain balanced panel tension;
Monitor fouling frequently;
Clean before openings become seriously restricted;
Remove leaves, plastic, seaweed, and floating debris;
Repair distorted or damaged sections;
Maintain suitable cage spacing;
Observe fish behavior during low-flow periods;
Monitor oxygen when stocking density or temperature is high.
These actions help keep the underwater highway open.
Two fishing nets with similar dimensions may behave very differently.
One may use heavier twine. Another may have more accurate meshes. One may be heat-set for greater dimensional stability, while another may change shape more easily.
A responsible buyer should compare:
Material;
Twine structure;
Diameter;
Strand count;
Mesh measurement method;
Knot type;
Panel dimensions;
Unit weight;
Border construction;
UV treatment;
Expected working environment;
Cleaning and maintenance requirements.
The cheapest net per kilogram or per square meter is not always the most economical option.
A poorly matched net may increase cleaning frequency, reduce water flow, create escape risk, or require early replacement.
The holes in a fishing net may look like nothing, but they perform essential work every second.
They carry oxygen-rich water into the cage. They allow heat and waste to move. They reduce pressure on the netting system and help maintain a suitable environment for aquatic animals.
The twine controls what remains inside. The open area controls what can pass through.
Good fishing-net design depends on respecting both.
A net must be strong without becoming unnecessarily dense, flexible without losing its shape, and fine enough to contain fish without blocking the water they need.
When buyers understand open area, they stop seeing a fishing net as a simple piece of mesh.
They begin to see it as part of an underwater life-support system.
For fishing-net purchasing, custom mesh openings, twine diameters, colors, panel dimensions, reinforced borders, or factory production support, visit our product collection or contact us directly to develop a net suited to your aquaculture environment.
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