Characterization of planktonic sea lice distribution and association to fish farm installations

Lepeoptheirus salmonis (Krøyer 1837) and Caligus elongatus (Normann 1832) are the sea lice species posing the biggest threat to both farmed and wild salmonid stock in the Northern hemisphere today. The three first stages are planktonic, and the transmission of sea lice within farms, and between farms and wild fish happens mainly in these stages. Today it is limited observation on planktonic sea lice distribution in and around fish farms, and it is a need for more knowledge on how the planktonic stages of sea lice are distributed in association to sea cages. Such knowledge is important to get a better understanding of sea lice dispersion and infection mechanisms at salmon farms. In this regard distribution of planktonic stages of sea lice inside and outside of sea cages in a fish farm were investigated by conducting horizontal plankton tows. The plankton tows were taken at two different farms, one wearing skirts and the other one without. How biofouling and washing activities may affect the distribution of sea lice were documented by taking plankton tows in relation to fouling on the net, and in different times of the washing cycle. A hatching experiment were conducted to characterize the planktonic stages of L. salmonis and C. elongatus, which was further used to differentiate between species in the plankton tows. The results showed that live planktonic L. salmonis and C. elongatus had characteristic pigmentation, and differed in size. However, due to loss of pigmentation, individuals fixated on formaldehyde (4%) could not be specified further than to family (Caligidae). Regarding the prevalence of L. salmonis and C. elongatus in Norway, it is likely that the planktonic sea lice found in the plankton samples belonged to these two species. The result from the plankton surveys showed that nauplii were the most abundant planktonic life stage in the water column at fish farms. Planktonic sea lice was shown to be retained inside the sea cages wearing skirts. No such effect of sea cages not wearing skirts were detected, and sea cage nets did not seem to hinder the transport of planktonic sea lice to the surrounding water to a very high degree. Biofouling of the net could to some extend retain sea lice inside of the cage, most possible due to reduced water flow. It was not found an elevation of sea lice larva in the water masses immediately after cleaning of the nets, thus it did not seem that the planktonic stages of sea lice stay in the biofouling, and it is not likely that cleaning activities of the sea cage could be a source of infection by releasing pre-infective and infective larvae

Biofouling on salmon pen nets and cleaner fish shelters does not harbor planktonic stages of sea lice

The objective of the current study was to determine the extent to which planktonic sea lice (Lepeophtheirus salmonis Krøyer, 1838 and Caligus elongatus Nordmann, 1832) were present in the biofouling on open-sea net pens used for commercial rearing of Atlantic salmon (Salmo salar L.), and to assess if biofouling organisms on nets act as barriers similar to salmon lice skirts. We have examined two possible interactions of biofouling and planktonic sea lice, the first was if biofouling could function as a microhabitat for planktonic sea lice, with resuspension of sea lice during net cleaning operations. The second interaction was if biofouling may cause a retaining effect on the transport of planktonic stages out of the net pen. These interactions were investigated at different commercial salmon farms. With only one sea louse found among the biofouling on nets and cleaner fish shelters, we found no indication that sea lice utilized biofouling as a reservoir. This was further supported by the lack of impact on the proportion of samples with sea lice and the average density of sea lice in the water following the release of biofouling material during in situ net cleaning. Furthermore, the presence of biofouling had no effect on the proportion of samples with sea lice or the average density of planktonic sea lice in the net pens. The presence of a lice skirt resulted, however, in a significantly higher proportion of samples with planktonic sea lice inside the net pen in one of the two sites utilizing lice skirts. The results of our study suggested that the presence of biofouling has no influence on the average density and proportion of samples with planktonic stages of sea lice and that planktonic sea lice do not inhabit biofouling.publishedVersio

Biofouling on salmon pen nets and cleaner fish shelters does not harbor planktonic stages of sea lice

The objective of the current study was to determine the extent to which planktonic sea lice (Lepeophtheirus salmonis Krøyer, 1838 and Caligus elongatus Nordmann, 1832) were present in the biofouling on open-sea net pens used for commercial rearing of Atlantic salmon (Salmo salar L.), and to assess if biofouling organisms on nets act as barriers similar to salmon lice skirts. We have examined two possible interactions of biofouling and planktonic sea lice, the first was if biofouling could function as a microhabitat for planktonic sea lice, with resuspension of sea lice during net cleaning operations. The second interaction was if biofouling may cause a retaining effect on the transport of planktonic stages out of the net pen. These interactions were investigated at different commercial salmon farms. With only one sea louse found among the biofouling on nets and cleaner fish shelters, we found no indication that sea lice utilized biofouling as a reservoir. This was further supported by the lack of impact on the proportion of samples with sea lice and the average density of sea lice in the water following the release of biofouling material during in situ net cleaning. Furthermore, the presence of biofouling had no effect on the proportion of samples with sea lice or the average density of planktonic sea lice in the net pens. The presence of a lice skirt resulted, however, in a significantly higher proportion of samples with planktonic sea lice inside the net pen in one of the two sites utilizing lice skirts. The results of our study suggested that the presence of biofouling has no influence on the average density and proportion of samples with planktonic stages of sea lice and that planktonic sea lice do not inhabit biofouling

Biofouling on salmon pen nets and cleaner fish shelters does not harbor planktonic stages of sea lice

The objective of the current study was to determine the extent to which planktonic sea lice (Lepeophtheirus salmonis Krøyer, 1838 and Caligus elongatus Nordmann, 1832) were present in the biofouling on open-sea net pens used for commercial rearing of Atlantic salmon (Salmo salar L.), and to assess if biofouling organisms on nets act as barriers similar to salmon lice skirts. We have examined two possible interactions of biofouling and planktonic sea lice, the first was if biofouling could function as a microhabitat for planktonic sea lice, with resuspension of sea lice during net cleaning operations. The second interaction was if biofouling may cause a retaining effect on the transport of planktonic stages out of the net pen. These interactions were investigated at different commercial salmon farms. With only one sea louse found among the biofouling on nets and cleaner fish shelters, we found no indication that sea lice utilized biofouling as a reservoir. This was further supported by the lack of impact on the proportion of samples with sea lice and the average density of sea lice in the water following the release of biofouling material during in situ net cleaning. Furthermore, the presence of biofouling had no effect on the proportion of samples with sea lice or the average density of planktonic sea lice in the net pens. The presence of a lice skirt resulted, however, in a significantly higher proportion of samples with planktonic sea lice inside the net pen in one of the two sites utilizing lice skirts. The results of our study suggested that the presence of biofouling has no influence on the average density and proportion of samples with planktonic stages of sea lice and that planktonic sea lice do not inhabit biofouling