Cleaner Fish Do Not Impact the Pigmentation of Salmon Lice (Lepeophtheirus salmonis) in Commercial Aquaculture Cages

Round 1

Reviewer 1 Report

Generally, the use of cleanerfish is not the only non-chemical way to treat salmon lice. It would be good to also mention this fact.

Line 69-71: the two sentences belong together?

If the position of the lice on the the fish affects the pigmentation of the parasites: where were the lice mostly positioned? Would it have been possible to collect lice from the dorsal and ventral side of the fish separately?

Why was the depth of the fish positioning monitored if the fish were only caught at the sea surface? The fish caught may have stayed close to the surface?

Why was Fig 8 not shown for cages with cleanerfish and without cleanerfish separately?

Can you repeat some of the comparisons with the biggest males and females only?

Author Response

Reviewer 1

Generally, the use of cleanerfish is not the only non-chemical way to treat salmon lice. It would be good to also mention this fact.

• We have added this information to the Introduction.

Line 69-71: the two sentences belong together?

• Yes, there was a comma (,) missing in this sentence and we have changed this.

If the position of the lice on the fish affects the pigmentation of the parasites: where were the lice mostly positioned? Would it have been possible to collect lice from the dorsal and ventral side of the fish separately?

In Hamre et al. 2021 the spatial distribution of male and female lice were very similar, with about 60% of individuals on the dorsal side of the fish while 40% were positioned ventrally. Thus, given the large number of potentially influential environmental variables at play in a commercial marine cage throughout production, we prioritized collecting as many lice as possible from as many fish as possible in varied conditions to maximize our ability to detect a trend in louse pigmentation with cleanerfish use, if present.

Why was the depth of the fish positioning monitored if the fish were only caught at the sea surface? The fish caught may have stayed close to the surface?

Salmon have a physostomous swim bladder and must gulp air to maintain neutral buoyancy. Previous work has shown that salmon in sea cages surface 1-4 times per day via observations of rolling and jumping behavior. When we have compared the condition factor and welfare of fish collected from cages using either a net pulled up from the deep or the jump-net used in this trial, we found that the fish are similar in size and condition between the two methods, with the jump net containing fewer ‘loser fish’ which tend to aggregate near the surface.

Why was Fig 8 not shown for cages with cleanerfish and without cleanerfish separately?

 - We certainly thought about presenting Fig. 8 in the way the reviewer suggests but Figure 3 already shows that there is no consistent pattern through time between cages with and without cleanerfish. In Figure 8, males and females follow a similar non-linear pattern through time, just with males consistently darker. We could remove figures 3 & 8 and create a figure with Treatment x Sex x Date, but that would be a much more complicated figure and just parse the data further to show the same results. Therefore, we have kept Figures 3 and 8 as they are and those in combination show the trend the reviewer is asking for.

Can you repeat some of the comparisons with the biggest males and females only?

• This is not necessary as the data shown in Fig. 8 is already compromised of adult (biggest) males and females.

Reviewer 2 Report

The article verified whether Cleaner fish does not impact the pigmentation of salmon lice (Lepeophtheirus salmonis) in commercial aquaculture cages. The presented topics are up-to-date, especially for the economic reasons and the commercial applications. The proper detection of salmon lice allows you to reduce losses related to the diseases they can cause. The research methodology described in the work contains the required information, as well as the research area. The presented topics are up-to-date and can be used in practice. The work is well organized with an introduction, the theoretical part, the presentation of the results and conclusions. After the theoretical part, the obtained results and their analysis are presented. Each part is correctly presented and correlated with the rest of the article.

Recommendations for improving the manuscript:

1. Please specify what is the scientific contribution of the authors?

2. Please specify the exact scientific purpose of the article?

3. Please describe the drawings presented in the article in more detail. What do they mean?

4. What is the beneficial effect of the research presented in the article on minimizing salmon lice?

5. Can the presented results be used in practice and how?

Author Response

Reviewer 2

The article verified whether Cleaner fish does not impact the pigmentation of salmon lice (Lepeophtheirus salmonis) in commercial aquaculture cages. The presented topics are up-to-date, especially for the economic reasons and the commercial applications. The proper detection of salmon lice allows you to reduce losses related to the diseases they can cause. The research methodology described in the work contains the required information, as well as the research area. The presented topics are up-to-date and can be used in practice. The work is well organized with an introduction, the theoretical part, the presentation of the results and conclusions. After the theoretical part, the obtained results and their analysis are presented. Each part is correctly presented and correlated with the rest of the article.

Recommendations for improving the manuscript:

1. Please specify what is the scientific contribution of the authors?

- This has been added.

2. Please specify the exact scientific purpose of the article?

- This has been added to the revised version of the ms.

3. Please describe the drawings presented in the article in more detail. What do they mean?

 Below are revised caption and figures. The figures and legends have been updated accordingly in the revised version of the ms.

Figure 1: Typical examples of each gender and developmental stage of mobile lice included in the dataset. From left to right, male and female pairs of pre-adult I, pre-adult II and adult salmon lice, respectively.

Figure 2. Two adult male L. salmonis with different degrees of pigmentation as measured by dMGV. The darker male on the left has a dMGV of 40.8 while the lighter louse on the right has a dMGV of 25.6.

4. What is the beneficial effect of the research presented in the article on minimizing salmon lice? 5. Can the presented results be used in practice and how?

Salmon lice exhibit a high degree of evolvability, and have become resistant to every chemical removal treatment developed thus far. These data suggest that, with the densities and species of cleanerfish commonly used in commercial salmon production, there is not strong directional selection on louse pigmentation. Lice, at least with regards to visual appearance, are not likely to adapt in a way which reduces cleanerfish efficacy anytime soon.  

We have emphasised this aspect of our research in both the Abstract and Key Contribution section of the revised version of the ms.

Author Response File: Author Response.pdf