Technology focus: Thermolicer and Environets17th December 2018

Knowledge Exchange Officer at the Scottish Aquaculture Innovation Centre (SAIC), Sam Houston, recently visited Marine Harvest Scotland (MHS) at their Kyle-of-Lochalsh shore base and a site near Portnalong. The purpose of the trip was to learn about three technologies that MHS has invested in with support from the European Maritime and Fisheries Fund (EMFF) and Marine Scotland.

Sam visited two vessels at Kyle-of-Lochalsh, the Bhein Bhan, a barge supporting Hydrolicer technology and the Orcadia II, a twin-cat workboat supporting Thermolicer technology. Both vessels carry out mechanical de-licing interventions at salmon producing sites on Scotland’s west coast.

At Portnalong, Sam visited MHS Environet trials to find out more about how the nets are managed at the site. This article will give an overview of Thermolicer and Environet technology. You can find out more about Hydrolicer technology in our previous blog.

Overview of Thermolicer technology

Thermolicer technology was first introduced to Scotland in 2016. It is a machine used to remove sea lice from salmon by bathing them in water which is moderately warmer than their current environment. The equipment is mounted onto a workboat, such as the Orcadia II, the salmon are crowded in their pen and drawn into the machine by vacuum pumps. The salmon must be separated from the seawater before passing through a circuit of lukewarm water, heated 24°C above the seawater temperature or a maximum of 34°C. Sea lice attached to the salmon do not tolerate the lukewarm water and respond by detaching from the salmon. After approximately 30 seconds, the salmon are separated from the treatment water and lice and returned to their cage. For a single salmon the treatment will last 60 – 90 seconds (the range is due to batch pumping). The result is that 90% of sea lice at all life stages are removed from the salmon without the use of any medications, which reduces any impact on the salmon and the environment. Simon Delvaux, De-licing Systems & Fleet Development Assistant Manager at MHS said, “The two Thermolicers operated by MHS have become indispensable in our strategy to control sea lice. Lice levels have been reduced at our sites and new technologies limit our use of medicines. Having a range of solutions gives us flexibility to manage our salmon effectively”.

Marine Harvest Scotland’s Orcadia II, berthed at Kyle-of-Lochalsh. This vessel currently supports Thermolicer technology and carries out de-licing operations along sites on the West coast of Scotland.

Before deployment in Scotland, Thermolicer technology was developed in Norway and Chile, by Steinsvik, a supplier of feed management systems and cameras to the aquaculture sector. After initial trials and further testing, the Thermolicer attracted the attention of the Norwegian Seafood Research Fund (FHF). Tore Laastad, Marketing Manager at Steinsvik said: “The introduction of the Thermolicer came at the exact right moment for the fish farming industry in Norway, and in just a few years, de-licing with lukewarm seawater has become the most frequently used method to combat sea lice.” Further tests were carried out in collaboration with several Norwegian producers and operators including: Blom Fiskeoppdrett, Kobbevik og Furuholmen oppdrett, Bolaks and Bremnes Seashore.

Overview of circular Environets

Sam’s next port of call was the MHS site at Portnalong, off the Isle of Skye, to visit commercial scale trials of circular pen Environets.

Circular Environets have been designed to address the issue of fish cage fouling. Fish cage nets submerged in seawater become fouled with time, but when the nets are dried, the fouling drops off easily. This drying technique has long been used to keep the nets on square pens clean which is important to ensure fresh water and dissolved gasses pass freely across the net. With the move towards HDPE circular cages, this concept had to be adapted for a circular pen. The Environet, a circular net and cage system, which won the Innovation Award at Aquaculture UK 2018, was designed by MHS Seawater Manager, David MacGillivray and developed in collaboration with Nets Shetland Services.

Environet trials off Portnalong. Note the drying net supported by the stanchions, ensuring the bulk of the net’s weight is supported by the floater tubes as opposed to the handrail tube.

The circular Environet involves two nets, which are stitched together at the collar, approximately half way round the circumference. One net holds the stock while the other dries, supported by four stanchions fixed to the floater tubes. The key management operation for the staff on site is changing the nets over, also known as “swimming” the nets. During the swimming, the net currently holding the salmon is taken into four free stanchions, opposite the four stanchions holding the dry net. The dry net is simultaneously released to keep the stock. See figure below.

Simplified schematic of the Environet technology, identifying the key components. The “swimming” of the net replaces the fouled net with the clean and dry net. First, the bottom of the net must be released from the sinker tube using the slider system (green), the net can be raised and by simultaneously releasing the dry net from the stanchions and taking in the fouled net the two halves are changed over. This process is managed in four stages using the internal net lines with aid of hydraulic winches.

Staff at Portnalong value working with the system and consider it the best way to keep nets clean. Site Manager, Kirk Jones said: “There is a lot to think about when conducting a swim; you have a chance to look closer at fish condition, fish behaviour and net condition and the process should be used as a great way to do this. The staff at Portnalong are now highly trained in swim throughs and have great attention to detail.” In addition to regular duties, staff can change two cages a day and since no net cleaning is required, no debris from this activity finds its way into the pen. The nets have been deployed at three MHS sites and more are planned in the future.


Marine Harvest Scotland is Scotland’s largest salmon producer and is developing new technologies to manage fish health issues on their sites across Scotland. Alongside Scottish Seafarms, Scotland’s second largest salmon producer, MHS reports that new technologies and tailored management have led to a reduction in fish mortality of 50%. The Scottish Aquaculture Innovation Centre is pleased to support this investment alongside Marine Scotland by directing EMFF funds.
With special thanks to all the staff at Lochalsh, Portnalong and the crew of the Orcadia II. In particular, Simon Delvaux, Kendal Hunter, Callum Nisbett, Kirk Jones and Danny Skinner.