Biofouling on Salmon Pen Nets and Cleaner Fish Shelters Does Not Harbor Planktonic Stages of Sea Lice

Abstract

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.

Planktonic and Parasitic Sea Lice Abundance on Three Commercial Salmon Farms in Norway Throughout a Production Cycle

“…Densities of planktonic sea lice can be described by mean abundance or a combination of the proportion-non-zero and average density (Jevne et al, 2020).…”

A Review of Factors Affecting Farmed Atlantic Salmon (Salmo salar) Welfare in Australia and Beyond

“…Cleaning of marine nets releases biofouling debris that can contribute to thrombi/subacute vascular lesions in the gills, although such effects may be limited to a small proportion of fish over short periods (Ostevik et al 2021). Early studies suggested biofouling communities may support microbial communities that lead to amoebic gill disease outbreaks (Tan et al 2002), but a more recent study suggests that is not the case (Jevne et al 2020). It appears net cleaning may be an important management procedure that can impact welfare by improving water flow or removing harmful organisms.…”

Monogenean Sparicotyle chrysophrii: The major pathogen of the Mediterranean gilthead seabream aquaculture

“…Namely, the presence of biofouling in open-sea Atlantic salmon cages showed no influence on the average density and proportion of samples with planktonic stages of sea lice, nor the planktonic sea lice inhabited biofouling. 123 While the Atlantic salmon and gilthead seabream farming technologies, as well as ecological and biological traits of the two pathogens, do not allow for direct comparison and drawing of generalised conclusions, the former study could serve as a robust background for similar research in the Mediterranean.…”