Aquaculture Magazine

February / March 2014

Sea lice Caligus rogercresseyi, a big threat to the Chilean salmon

By David Ulloa

The parasitic copepod has been present off the coast of Chile long before aquaculture developed and also affects wild fish. 

Caligus rogercres­seyi is an ectoparasite exclusively found in sea environments; its common name in Chile is caligus. It was first described in 1997 and its presence has increased due to its capacity to infest salmon, particularly Atlantic salmon (Salmo salar) and trout (Oncorhynchus mykiss) (it also affects Coho salmon (Oncorhynchus kisutch) to a lesser extent). These three species are commercially cultivated in Chile, and together reached a total production of almost 750,000 tons in 2013.

Cause of severe problems

During the crisis caused by the Infectious Salmon Anemia (ISA) virus in 2007, the main vector that helped the spread of the disease was caligus. High parasitic loads were recorded, reaching more than 35 parasites per fish, and these high loads were responsible for  immunosuppression that facilitated the emergence of the virus, also  as a gateway to other viral and bacterial diseases.

In early 2010 the presence of caligus had been markedly reduced due to the contraction of the post-crisis industry, with fewer operational sites and production  levels of less than 200,000 tons by mid-2009.

This promoted better sanitary conditions on farms and led to excellent results in production. Combined with a higher market price this allowed the industry to have a quasi-miraculous recovery, which is used as a successful case analysis in graduate business programs in Chile. 

Repeating the mistakes from the past

However, the story doesn’t end there. A huge temptation to regain the time lost and to reverse the negative results caused by the crisis promoted the reopening of many farms and an increase  in stock densities, as shown in the data obtained in 2012, with a total stocking of more than 235 million smolts and a monthly biomass up to 600,000 tons in October  across 600 production facilities.

Therefore, after a couple of years and with greater biomass  per unit area, history repeats itself and this is once again putting the industry before one of its greatest threats, caligus, which is recovering prominence and reaching dangerous levels that put the industry at risk. This has encouraged the public and private sectors to develop new strategies to face the problem more effectively in the long term.

Program against Caligidosis

In 2012, the National Fisheries and Aquaculture Service (Sernapesca) updated the Specific Sanitary Program for Surveillance and Control of Caligidosis. Changes to the 2007 program include greater background research, organization of farms by new geographical districts and better collaborative efforts between producers. It also emphasizes surveillance and monitoringfor presence and abundance of the parasite, in addition to control activities  required by regulations and the imposition of sanctions in cases of non-compliance.

The Program defines High Dissemination Centers (CAD) as those having average parasite loads of 9  Caligus per adult fish. Any culture facility that exhibits this amount of parasites in three weekly samples  over 6 consecutive weeks will be subject to early harvest of infested biomass.

Meanwhile, producers are aware of this threat, and have redoubled their efforts to beat it. Cooperative work between producers is the key to success in both implementation of coordinated treatments and information sharing.

Efforts of the Industry

The Technological Institute of Salmon (INTESAL) – a technical agency associated with the Chilean Salmon Union (SalmonChile) - has played an important role in addressing this issue, through the organization of activities that enhance  methods to face caligus in effective ways.

Many Research Centers and Universities have addressed the problem from different angles and are now developing new knowledge about the parasite. They enjoy the support of the entire industry, including producers, equipment developers and distributors.

The Parasite

The parasite presents eight stages. Three of them are planktonic: Nauplius I, Nauplius II, and copepod (infective stage). Subsequently, in the fish, stages are Chalimus I, II, and III. Finally, the parasites reach the adult stage (male or female) and produce eggs.

The parasite’s life cycle is modulated by temperature, e.g. at 12º C the parasite lives approximately one month. Ideal salinity  for Caligus rogercresseyi is 30 ppt. At salinities below 15 ppt, the parasite experiences development problems and it cannot survive in fresh water. When it attaches to the fish by its frontal filament, the parasite feeds on mucus and blood, thus harming the skin and damaging this important protective barrier against other disease organisms.

Treating caligus

There are several therapeutic alternatives that are being used in Chile for removing these parasites, such as Pyrethroids, synthetic insecticides such as Deltamethrin and cypermetrhin, organophosphates such as Azametiphos and disinfectants such as hydrogen peroxide. They are mainly applied as baths in enclosed environments or in specially designed boats for fish transportation.

There is also an oral medication – diflubenzuron and emamectin benzoate, that can be mixed with the feed. Producers take into account the required withdrawal periods, which are at least one to two months. A very important measure is the use of drugs in rotation, since prolonged use of the same active ingredient generates drug resistance after a couple of years.

Regulations on Closed Containment Baths

One of the most recent measures to control the disease  imposes the obligation to apply anti-caligus baths in closed systems. It was issued on June 1st, 2013.

Similar rules have applied in Norway since January 2011, where the use of closed systems is a requirement, based on the logic of subjecting the parasite to antiparasitic agents more effectively and avoiding the dilution that occurs in traditional systems, where the cage perimeter is covered to only 4 or 5 meters depth, but the bottom remains open.

Experiences

In Chile, logistical considerations and the effect of ocean currents are factors that require special attention and constitute an additional problem to implement the canvas-enclosed treatment systems. In spite of this challenge, many producers have found solutions that enable them to meet the regulation and, more importantly, do it effectively and safely.

The noteworthy initiative by AVS Chile, called “Generation of a manual of operative procedures and recommendations for optimizing therapeutic baths against caligus” was attended by seven companies, the INTESAL and two supplier companies (one of which was Storvik).

As for equipment, all boats and platforms where treatment operations will take place, along with canvases, O2 supplies, air blowers, oxygen meters and systems for the distribution of the diluted medication must be pre-verified and be in top working order. All safety equipment and procedures must be available at all times and all personnel must be able to use them.

 There are, however, still no accurate, auditable parasite counting systems, and  systems for dilution and distribution of therapeutics must be improved to avoid overdosing and sub-dosing zones.

In this context, international companies are already working on the development and validation of an efficient device for counting salmonid ectoparasites; this is the Innova-CORFO (by the Production Enhancement Corporation – a government entity that co-finances innovation) project. This team will allow researchers to capture images for an accurate assessment of Caligus rogercresseyi numbers. Moreover, there is already a device, the Sprinkler Drum, which will soon be on the market and has been designed to  produce accurate dilutions and distribution of drugs during treatments.

Information on Costs

High levels of caligus on farms mean an increase in the frequency of baths that are made at authoritized times during the production cycle, easily reaching 12 treatments annually. It is estimated that the annual cost for this practice is around USD$40-45,000 per cage.

While the treatment is effective, the rate of re-infestation is so high that it minimizes or even nullifies the desired effect. That’s why a coordinated approach is the key to success, as baths synchronized within production areas enhance the procedure’s efficiency.

Along with high levels of caligus and other sanitary issues such as the Salmonid Rickettsial Septicemia (SRS, the main disease diagnosed in 2012), higher costs associated with new regulations and the general rise of inputs (feed, energy, etc.) have led to an alarming increase in total production costs of Chilean salmon. They amount to more than USD $4/kg, thus causing the industry to surpass the production costs of their Norwegian peers.

New Strategies

In the search for new alternatives, the use of high quality smolts is a priority, as fish will be more healthy, resistant and genetically strong. It is also important to lower densities to 12 kg/m3 and to allow sites to fallow between crops.

Additional strategies include the use of functional foods with nutritional factors that confer resistance or greater protection to fish against the parasite. In Norway there are ecological or so-called “organic” alternatives with species such as wrasse and lumpfish, cleaner fish that allow a better, biological control of parasites.

Producers must keep these considerations in mind:

  • The use of vaccines;
  • The development of resistance by genetic selection;
  • Investigate those factors that make the mucus of coho salmon less susceptible to caligus infestation;
  • The use of automatic feeding systems with submerged distribution to keep the fish away from the first few meters in the cages, thus lessening the interaction with the infective stages of the parasite that concentrate on the surface;
  • Prioritize the use of farms with salinity below 25 ppm, or use estuarine waters. 

Conclusions

The salmon industry provides excellent quality protein and high nutritional value for human consumption; it’s an industry with a great outlook and a growing industry that increases 6% year after year.

Accordingly, there must be an increase in Investments, Development and Innovation (I+D+I), in order to continue feeding 7 billion people in a healthy way.


David Ulloa

David Ulloa has a degree in Biology and holds a Masters in Business. He is the current General Manager of Storvik, a company dedicated to selling technological solutions for automating aquaculture processes.

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