The use of Stingray optical delousing™ technique to control sea louse abundance under commercial conditions

Introduction

Stingray Marine Solutions AS (SMS) has designed a novel delousing method using a platform called the "Stingray". The need for a continuous, non-invasive, technological solution has been recognized to control the sea louse situation on farmed Atlantic salmon (Salmo salar) (Aaen, et al., 2015). In Norway a sea louse control guidelines are based on the number of sea lice in the adult female stage which infect a fish. This "trigger level" is fixed at 0.5 adult female lice per fish. The Stingray platform aims at keeping louse levels below this trigger level, which, when exceeding, will require an anti-louse treatment to be carried out. The platform is a vision based system which optically identifies sea lice, Lepeophtheirus salmonis, on farmed salmon. Lice are removed through a guided laser pulse; a method referred to as optical delousing. The Stingray system detects and targets all stages from pre-adult I ♀ and pre adult II ♂ up to adult male and adult female, thus creating a top-down control of the louse life cycle.

Delousing efficiency by the system has been tested commercially on both 1^st year and 2^nd year at sea fish with good results, irrespective of fish size. Additionally, delousing efficiency has been tested scientifically on 2^nd year at sea fish. A significant effect of stocking density on laser delousing potential was observed. Consequently, for commercial use of the system, a low salmon stocking density is currently not advised by SMS.

Materials and Methods

Commercially, a set-up of 1-2 lasers per pen in at least 50% of pens / location is currently used by all Stingray users. A Stingray laser unit (called the "Stingray node") consists of a control cabinet, providing internet and electricity, a floating buoy unit (BU), controlling the mechanics and a submerged laser unit (SU) controlling the laser and guidance systems (Figure 1). The systems operate using 240V standard electricity and are "plug and play". All operations are automatized and no further effort is required to ensure delousing.

The overall node weighs 300kg in air, but through the use of floating elements, the weight in water is reduced to 30kg. The node requires a stable 220V electricity supply and a working internet connection. Node movement and fish finding can be achieved manually, remotely, or through a software called the Stingray FishFinder™. Sea lice in fish passing in front of the detection cameras and laser system will be detected, targeted and killed. The laser has a focal point of 90 cm in sea water, at which distance maximum energy will be exerted into the sea louse. The operating distance of the laser was found to range from 30 to 150 cm.

Results

Scientific trial

Laser delousing efficiency on a commercial scale has been tested in a long term trial in Norway against delousing efficiency of cleanerfish. In 15 weeks of trial, one anti-louse treatment per pen could be avoided through the use of the Stingray laser. Overall sea louse abundance was lower in laser pens (21%) and adult female louse abundance was lowered by 8%, on top of avoiding 50% of anti-louse treatments in the trial period. The treatment intervention period, i.e. the time span between required treatments, has been increased from 6.5 weeks to 11.5 weeks (Figure 2).

Commercial experience

Stingray optical delousing systems have to date been installed at 24 locations in three countries. Overall results from all locations show lower louse abundance. By continuously reducing adult sea louse numbers, a preventative effect on louse build up is observed. To date over 30 000 tons of laser treated fish have been harvested with no signs of ill effects due to the treatment. Generally, fish welfare is expected to be improved through less handling of the animals and reduced treatment interventions.

Discussion and conclusion

The Stingray laser platform has been proven effective at controlling and slowing sea louse recruitment on farmed Atlantic salmon in commercial operations. The system is autonomous and automated, effectively reducing work required for fish farmers. A reduction of louse abundance as well as a reduction of treatment interventions was observed in the trial, leading to improved animal welfare, better louse control and lower costs. The system can be used alongside any other treatment types, but is currently consider one of the gentlest delousing methods available (Svåsand, et al., 2016).

References

Aaen, S. M., Helgesen, K. O., Jørgensen Bakke, M., Kaur, K. Horsberg, T. E., 2015. Drug resistance in sea lice: a threat to salmonid aquaculture. Trends in Parasitology 31:72-81.

Svåsand, T., Karlsen, Ø., Kvamme, B. O., Stien, L. H., Taranger, G. L., Kroon Boxaspen, K., 2016. Risikovurdering norsk fiskeoppdrett 2016. Fisken og havet, særnummer 2-2016, Havforskningsinstituttet periodical. Available at http://www.imr.no/filarkiv/2016/04/risikovurdering_2016.pdf/nb-no (accessed 5^th July 2016) (in Norwegian).