ANTIPARASITIC ACTIVITY OF THIOSULFONATE AND THIOSULFINATE GARLIC DERIVATIVES AGAINST SEA LICE. IN VITRO AND IN VIVO EVALUATION.

Núñez C*, Trouerbach A., García JD., Guillamón E., Baños A.
 
DMC Research Center S.L.U. Camino de Jayena s/n, 18620, Alhendín, Granada (Spain).
E-mail: cristinanl@dmcrc.com

Introduction

Sea lice, copepods of the family Caligidae, are the most significant parasitic pathogen in salmon farming in Europe and America, it is estimated to cost the world industry 300 million euros a year and may also be pathogenic to wild fish. Lice may also act as vectors for the transmission of viral and bacterial pathogens.

Caligus rogercresseyi is the most important parasite affecting salmon and rainbow trout farming in the Southern Hemisphere, with an incidence of 99% in Chilean farms.

The current control methods for sea lice are based on chemical products, mostly costly and not effective enough.

This study aims to evaluate the effect of two garlic thiosulfonate and thiosulfinate derivatives on the in vitro antiparasitic activity against Caligus spp. and the in vivo effectiveness of a supplemented fish diet with the natural product AQUAGARLIC® containing the two garlic compounds.

 

Materials and methods

Wild adult females and males were isolated from a salmon farming industry in Chile to obtain caligus. Caligus spp. were kept in filtered seawater (125 µm membranes) in absolute darkness inside a thermo-regulated chamber at 12ºC.  The egg sacs were removed gently from females using a fine-tipped forceps and placed in separate beakers with 500 mL of filtered seawater in the conditions described above until spawning. Then, the different stages were separated as Nauplius I, Nauplius II, and Copepodite for subsequent in vitro susceptibility studies.

To evaluate the antiparasitic activity by means of effective lethal concentration and survival ratio, the three stages of Caligus were placed in 10 individuals per sterile petri plate. Concentrations of 100, 200 and 300 mg/kg of a mixture of the two garlic derivatives thiosulfonate and thiosulfinate were tested for each stage by adding the concentration in the petri plate over a 30-minute exposure period. After that, the water was changed and they were incubated at 12ºC during a 12-hour photoperiod. Observations were registered after treatment using the Kaplan-Meir function.

In vivo experiments took place at a salmon farm in real conditions. Salmon were separated into two groups, the first one received a control diet and the second one was fed with a supplemented diet containing 50 mg/kg thiosulfonate and thiosulfinate garlic compounds (AQUAGARLIC®). To determine the effectiveness against Caligus spp., the incidence of Caligus in each group was evaluated during a total period of 90 days.

 

Results and discussion

Thiosulfonate and thiosulfinate compounds demonstrated an antiparasitic activity against different life-stages of Caligus spp., with significant reductions of survival probability (Fig. 1). Significant effect was observed at the highest concentration of 300 mg/kg of garlic derivatives compounds with a survival probability of 0% after 15 minutes of exposition.

In vivo experiments showed a significant reduction in infestation incidence of Caligus spp. in fish that were fed with 50mg/kg of AQUAGARLIC®-supplemented diet. The group of salmon that were fed with a control diet presented a high ratio of number of ovigerous female per fish. When the level of ovigerous female Caligus spp. ratio were up to 1.5, a traditional control method of the parasite based on hypochlorite baths, was applied. Whereas the control group needed a total of 3 baths, the group of salmon that were fed with AQUAGARLIC®-supplemented diet did not need any bath along the period of the experiment.

 

Conclusion

Thiosulfonate and thiosulfinate compounds were found to be an effective natural antiparasitic solution against Caligus spp. in both in vitro and in vivo essays, being able to reduce the survival probability of this parasite. The results indicate the protective effect of the two garlic derivatives against Caligus infestation in salmonids and, furthermore, the potential of this natural product as a AQUAGARLIC®-supplement in diets, as a new alternative to current chemical methods for controlling Caligus spp. and other sea lice parasites in salmon farms.