What do Tunnel and Zander have in Common?

Success Stories18 Sept 2020

At first glance, nothing. But there are similarities. In this blog post you can find out which and how Leister extruders are used for welding the huge PE tanks for the sustainable pike-perch breeding "Basis 57" in Erstfeld, Switzerland.

Author: Silke Landtwing, Manager Corporate Communications, Leister Switzerland

The tunnel is originally dark. Zander (scientific name: sander vitreus) are predatory fish and are therefore more likely to be found at the bottom of lakes, because they do not want to be seen by their prey and their enemies. Water: Water is a nuisance in the tunnel, which is why the tunnel walls are lined with plastic membranes for sealing. These are then welded with Leister equipment. Zander need water to live and the cleaner the better. This is where the threads come together in the start-up 'Basis 57 nachhaltige Wassernutzung AG' in Erstfeld, Switzerland.

Sustainable use of water from the Gotthard Base Tunnel

Welding the 57 km / 35.4 mi long Gotthard base tunnel was a major project for Leister, which we reported on in our blog.

The mountain water, which is drained from the Gotthard base tunnel of the NRLA (NRLA means New Railway Alpine Transversal) through plastic membranes welded with Leister equipment, is not only particularly clean and thus extremely fish-friendly, but also ideally tempered at 12 - 14°C / 53.6 - 57.2 °F.

Creative minds from 'Basis 57' have therefore considered using this water sustainably and sensibly. There were many ideas. By the way, brewing beer with it was also part of it. Also to breed pangasius or burbot was under discussion. The zander, also known as walleye or pike perch won in the end. Why? You will find out in this blog post, because we were on site for you and visited the test breeding facilities.

That much up front: All those who like to eat fish can be happy. Since the walleye is a particularly noble and fine edible fish, they will soon be available in this country from sustainable fish farming in Uri, thanks to 'Basis 57'.

About the company 'Basis 57' 

"The start-up company 'Basis 57 nachhaltige Wassernutzung AG' - which stands for  'Basis 57, sustainable water usage corporation' - was founded more than ten years ago, when the NEAT project was at its peak," explains Myriam Arnold, responsible for communication and marketing at 'Basis 57'. When it came to how to use mountain water sustainably, many possibilities were discussed. "After all, the greatest potential has been seen in edible fish, which is why 'Basis 57' is now focusing on zander fish farming. This with the goal to breed this kind of fish in the canton of Uri in a sustainable way", Myriam Arnold continues.

Pike perch and pike perch aqua farming

Solt Sokoray-Varga, production manager for fish farming at 'Basis 57', has been professionally engaged in pike perch and pike perch farming for many years.

Author's note: The zander stocking fish at  'Basis 57' weigh about 10 g / 0.35 oz and are about the size of a finger. You can find more information on the company's website.

While Solt Sokoray-Varga shows us the plastic tanks with the pike-perch seedlings in the fish farm, we learned a lot of interesting things from him. Especially since it is not an easy task to breed zander. On the contrary: It requires a lot of expertise and tact: the sensitive predatory fish need darkness, peace, clean water, the right water temperature and precisely dosed dry food so that they feel good and grow up healthy. This is another reason why the fishes well-being is the top priority in pike perch farming. Solt Sokoray-Varga knows from experience, "If the walleye isn't comfortable, it won't grow."

Good reasons for sustainable zander fish farming

In Switzerland, there are only a few zander breeding farms so far. One of them is the company 'Basis 57'. This is an advantage on the market and, in addition to the walley's popularity as an edible fish, is one of several reasons why 'Basis 57' has chosen the pike perch despite all the challenges.

Due to its white, firm flesh and the unmistakable fine taste of boneless fillets, the pike perch (scientific name: sander vitreus) is a highly sought-after edible fish. Another important point: Fish consumption in Switzerland is very constant: Around 70,000 t / 77.162 t of fish land on Swiss plates every year. The majority of the pike perch (over 90 percent) have to be imported. For those interested in learning about short transport routes, animal-friendly care, sustainable and ecological fish farming in guaranteed clean water will surely prefer Uri's walleye.

Why are breeding tanks made of thermoplastic material?

In fish farming, concrete tanks or tanks made of other materials are often used, besides plastic tanks. We asked managing director Thomas Gisler why the management at 'Basis 57' decided to use plastic pools made of polyethylene (PE):


"PE pelvises fit in terms of stability and are also good in terms of price. In addition, PE has the advantage over concrete or other materials, making it easy for the fish tanks to be adapted more quickly if necessary, so we remain more flexible in operation.

Can PE actually be recycled? We ask Reto Britschgi, plastic fabrication specialist at Leister: "Yes, PE is 100% recyclable, which of course fits in perfectly with sustainable fish farming." How does recycling work? Containers, pipes or receptacles made of PE that are no longer needed are sent to a shredder. The shredded PE is then granulated and the resulting PE granulate is reprocessed. In addition, the plastic PE is particularly easy to clean and offers very little adhesive surface for germs. Reto's conclusion: "Due to its properties, PE is ideally suited for tanks used in sustainable fish farming."

How many pools are needed and what do they look like?

PE tanks of different sizes are required for pike perch breeding at  'Basis 57': These are 12 large pools, 6.8 m / 2.3 ft. in diameter and 4 m / 13 ft. high, while the six, smaller pools are 4.8 m / 15.7 ft. in diameter and 4 m / 13 ft. in height. The pelvic wall has a thickness of 2 cm / 0.8 in. each case.

In order to keep the light reflection as low as possible, the pools are made of black PE. Unfortunately, bright light disturbs and stresses the zander. The  'Basis 57' staff responsible for breeding therefore wear headlamps at work so that they can see something in the sparsely lit and almost dark rooms with the breeding pools.

Colasit welds breeding tanks with Leister extruders on site

Why is Leister interested in pike-perch breeding at  'Basis 57'? We have good reasons for this: Sustainability has always been our central focus at Leister, and we are committed to this with our durable products, climate-friendly company buildings and careful use of natural resources, among other things. We always find it exciting when our products are used in terms of sustainability. Therefore, we are very pleased that Colasit AG, a Swiss company that specializes in plastics processing, is building the pike-perch ponds made of PE here at  'Basis 57'. Leister has enjoyed a long and successful partnership with Colasit, which will continue for many years to come. Once again, the experts at Colasit are relying on high-quality, low-noise Leister extruders. Many thanks to  'Basis 57' and to Colasit for their great cooperation. We appreciate the opportunity to be on site to film and take pictures.

How a fish tank is created


In the video you can see how the PE fish tank from Colasit is welded with the Leister WELDPLAST S2 extruder. Specifically, the wall of the pool is welded to the floor so that the pool will later remain watertight and withstand the high pressure.

We looked over the shoulder of professional welder Piotr Kurys (a mechanic at Colasit) while he was working and he told us what he appreciates most about the Leister extruders: "I prefer to work with Leister extruders because they are so quiet."


On this picture you can see that the blower motor of the WELDPLAST S2 is located at the head height of Piotr Kurys during welding. At 21 m / 68.9 ft. welding seam (the outer wall of the large fish tanks measures 21 m / 68.9 ft. each) and a welding speed of 25 cm/min. / 9.84 in/min., Piotr has about 85 minutes of "extruder sound" in his ear, if he doesn't take a break. No wonder he is pleased with the quiet Leister extruders.

Additionally, the ergonomics of the extruders also make long jobs easier. When welding such large projects, it is important that workers can hold the extruder in a certain position safely, stable and for a long period of time without tiring or cramping during welding.


Here is a photo of the finished breeding tanks. Soon zander fish will be swimming and growing up here in Erstfeld Uri in pure mountain water.

The first pike-perch fillets from Uri are expected to be available summer 2021

Thomas Gisler is confident: "If everything goes according to plan, the first pike-perch fillets will be available for purchase in the company's own shop beginning summer 2021. You will then find the fine walleye fillets of Uri on the menu in select restaurants. We regularly publish current information on the website of  'Basis 57'."


Contact for extruders and tank construction

Reto Britschgi, Product Manager for extrusion welders, is your competent contact person for all aspects of Leister extruders and container construction. If you have any questions or need advice, please contact him.