New methodology for bath treatments Fine-tuning the use of whole tarpaulins

By Christian Perez Mallea

In the middle of last year, the National Service of Fisheries and Aquaculture (Sernapesca) determined that the use of closed systems during delousing treatments was going to be mandatory . At first, the standard established June 2013 as a starting point for implementation.

That is when the local salmon producing companies should stop using tarpaulin skirts during bath treatments and begin using whole tarpaulins or treat inside wellboats. Moreover, by the end of 2012, Sernapesca, anticipating the implementation of this regulation, established that the compliance with this new measure can be required ahead of schedule, depending on the historical loads of sea lice in each neighbourhood.

Shortly after the Authority announced this regulatory change, a number of salmon producing companies started applying the bath treatments under the new requirements. Along the way, those companies had to deal with several inconveniences related to the adaptation of a technique which is already implemented in Norway, to the particularities of the Chilean farms. In turn, arguing in favour of this change, Alicia Gallardo, Head of the Aquaculture Department of Sernapesca, recently revealed that, according to the statistics of after-treatment reports, the whole tarpaulin method has been more effective than tarpaulin skirts.

Bath treatment in Mainstream Chile

The following is a description of the delousing treatment against sea lice (Caligus rogercresseyi) conducted by the staff of Mainstream Chile in one of the cages of the farming site “Chidhuapi 2”. This site is located next to the small island of the same name (near the town of Calbuco, in the Los Lagos Region) and situated in the neighbourhood 3A. The delousing product chosen by the company on that occasion was Alpha Max (deltamethrin 1%). This farming site consists of a module with 16 30m x 30m metal cages. The Atlantic salmon treated had an average weight of 2,7kg. As in other companies, Mainstream Chile employs diving services before and after the administration of bath treatments to support the lifting and mooring of nets and to release them once the process is concluded. The following report details some of the routines performed by Mainstream Chile during delousing treatment with deltamethrin. These may have similarities with other routines in other salmon producing companies, but are not necessarily the same. On average, the company is capable of treating four cages per day using this methodology.

Description and timing of the process Sernapesca has established a set of rules for the use of pyrethroids (deltametrine and cipermetrine) in the country. This requires scheduling delousing treatment within a time frame determined by the Authority.

Furthermore, the Form for Delousing Treatment (FTA according to its Spanish initials), designed by Sernapesca for companies to report the beginning of delousing, has to be completed. This form details the time frame and products used in the treatment. January 16th: The Veterinarian submitted an FTA to Sernapesca, describing the specie to be treated, the average lice per fish in the farming site, what technique will be used, and which, product will be used, and in which concentration it will be used. January 18th: Sernapesca approved the request. After that, the Veterinarian completed the Veterinary Medical Prescription (PMV according to its Spanish initials) required for procuring the delousing product. * 24 hours prior to treatment, all fish in this farming site were put on a fast. January 22nd 9:00 - 10.30 am: Before our arrival a delousing bath treatment was performed in one of the cages of the ‘Chidhuapi 2’ site. 10.45 am: We began our visit to the fish farm. Almost at the same time, in order to prevent the oxygen content from falling below 4mg/l, they began administering additional oxygen to the next cage to be treated. To perform this task, the company tested a nozzle similar to that used by fire fighters. Over time this pump has been replaced by a perforated pipe. In future bath treatments the company intends to use a perforated ring-shaped hose. 11:00 am: The team specialized in bath treatments lifts the fish net up to 4 meters depth. Meanwhile, the barge working with this team is now berthed next to the cage. This vessel has a deck for manoeuvring, a windlass and a hydraulic arm.

The sides and bottom of the cage are enclosed with a 43 x 43 meters plastic tarpaulin to separate the water where the fish swims from the rest of the water column. This tarpaulin is moved from the outer to the inner sides of the cage. The work team uses a windlass to easily lift the tarpaulin. Then, the tarpaulin is tight from central joints and two corners and, after that, it is tied along the entire perimeter of the cage. At the same time, the corners of the cage are lifted a little bit to get a better fit and are subsequently lowered again to their normal level after the tarpaulin has been placed in position. 11.30 am: Two specialist workers start preparing the delousing solution with all the necessary safety equipment (nitrite gloves, disposable overalls and a full face mask).

11.35 am: The solution is distributed through the diffuser equipment. This process should only be interrupted if the oxygen levels (which are monitored at all times) fall to critical levels.

12.05 pm: After half an hour in which the fish were in contact with the delousing solution, the tarpaulin is pulled out while the oxygen supply is maintained for another 30 minutes. * Usually, fish are not fed before 24 hours after the treatment.