In fish farming use, the standard method is to install the Flexi-Panel into a sweep net, which is used to enclose all the fish in the cage. The sweep net is then gradually lifted, thus encouraging the smaller fish to swim through the openings in the Flexi-Panel, back into the cage. The grading is completed when only the larger fish, unable to pass through the Flexi-Panel, remain in the sweep net.
Whilst the principle of passive grading is not new, the 'Flexi-Panel' represents a massive step forward in terms of technology. Other grading grids can offer only a restricted 'grading panel area' due to their weight and rigid construction. As well as tending to cause physical damage and scale loss to the fish, these rigid grids did not provide a large enough area to allow a quick and stress free method of grading large tonnages of fish.
Flexi-Panel's lightweight flexible construction overcomes all these previous drawbacks, allowing very large areas to be easily and safely handled. When the Flexi-Panel is in use the tension on the net keeps the individual apertures at their pre-determined dimensions, thereby allowing an accurate size grade. However, when the tension is removed from the panel it simply folds up in any direction, just like an ordinary net.
The strength, flexibility and lightweight nature of the Flexi-Panel comes from the materials used in its construction. Relatively short lengths of very rigid uPVC pipe are connected together using loops of Dyneema twine to form a series of individual apertures. (Dyneema was chosen as it is the strongest, most stable and abrasion resistant material available). The plastic pipes are very smooth and are able to rotate, thereby completely eliminating physical damage and scale loss to the fish.
Large areas of Flexi-Panel can easily and safely be used, resulting in fast and stress-free grading of the fish.
Flexi-panel is most commonly used for passive grading, splitting the population in a cage to allow for selection and harvesting of the larger, faster-growing fish.
Once the grading operation is complete (when all the smaller fish have swum through the openings in the Flexi-Panel), you can either harvest the remaining larger fish directly from the sweep net or transfer them to another cage for harvesting at a later date.
With the appropriate size of aperture you can, of course, use the Flexi-Panel to size grade your fish at any stage of their growth. The clear benefit of this is that removal of the larger and more dominant fish allows the smaller fish to grow more quickly.
Popular sizes of Flexi-Panels for grading farmed salmon are 10m x 6m, 15m x 6m, and 20m x 10m, but there are no limitations to size. The individual apertures within the panel can also be made to any dimension, with increments of 1mm, the width determining the size of fish that can swim through.
Any size and any aperture can be made as each Flexi-Panel is constructed to the individual customer specifications.
For most species of farmed fish there is an optimum harvest size, where fish achieve a premium price compared to smaller undersized fish. Therefore a method of selecting the prime fish for harvest, whilst allowing the smaller ones to continue growing, will provide the farmer with a greater tonnage of fish and the maximum possible income. This is exactly what the 'flexi-panel' does. The direct financial benefit of using the Flexi-Panel to size grade farmed salmon prior to harvest can clearly be seen in the following example, which is taken from actual harvest results.
Flexi-Panel In Use - Real Life Example
A farmer with a two essentially identical cages, each containing approximately 195 tonnes of salmon with an average weight of 2.87kg, required to harvest approximately 40 tonnes. Comparison of un-graded harvest versus 'Flexi-Panel' graded harvest.
13,616 fish harvested (ungraded) value £126,670
Flexi-Panel Graded Harvest:
9,892 fish harvested (large graded) value £137,726
Benefits of size-grading prior to harvest:
- £11,056 EXTRA income to the farmer for harvesting 3724 FEWER fish.
- The average harvest weight increased by 1.08Kg
- The average price per fish increased by £4.62
- The 3724 extra 'un-harvested' fish will continue to grow to be harvested at a later date for an additional projected income of approximately £35,000.
- Based on these figures the 'Flexi-Panel' system pays for itself in one use.
Other Benefits Of Flexi-Panel:
The wider benefits of using Flexi-Panel include the following:
- Flexi-Panel is very light and easy to use compared to rigid graders.
- The grading operation is very quick and simple to carry out even with large cages and large tonnages of fish.
- The larger the size of grading panel the quicker the grading operation is completed therefore the less stress is put on the fish.
- The large dominant fish are selected for harvest.
- Small fish are not harvested and are therefore grown on to a larger size.
- Continuity of supply of the correct size of fish can be achieved.
- Growth rates are increased as the density is reduced.
- The Food Conversion Rate (FCR) is lowered by always selecting fish for harvest at the optimum size.
- The lower FCR means that you can achieve lower production costs.
Welfare Benefit Of Flexi Panel
Using 'Flexi-Panel' greatly improves fish farm productivity and efficiency as well as boosting the image of farmed fish.
It is widely recognised that 'passive grading' methods are best for ensuring the welfare of farmed fish.
Compared with other grading methods, the welfare benefits include:
- Reduced stress
- Reduced physical damage
- Reduced risk of handling related disease outbreaks
- No starvation required prior to grading, so no loss of growth
The Organic Food Federation - an organisation tasked with the accreditation of organic farmed fish production in the UK - has stipulated the requirement for the use of passive grading systems for all size grading operations in their 'Standard for Aquaculture'. A representative from the OFF said; 'The Flexi-Panel grading system meets all our requirements'.