Evaluation of Three Atlantic Salmon Strains for Resistance to Copepodid Sea Lice Attachment
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis study presents a novel and interesting approach to understanding this host-parasite interaction. The hypotheses are well formulated, and the experimental design straightforward to adequately address the research question. I enjoyed reading the manuscript - it is eloquent but concise, and information is presented comprehensively whereby the details I was expecting were indeed mostly there.
Although you do address the issue of large variation between tanks, I would have liked to see some discussion elaborating on why substantial differences were observed among replicate tanks, and how this influenced your conclusions. Otherwise, the discussion section adequately and concisely addressed a convoluted topic, so well done.
Specific comments:
L25: For me, "challenge-specific" variability was unclear in terms of what measure you were referring to.
L54-56: Perhaps revise sentence, particularly clarifying or rephrasing "preventing lice attachment simultaneously or in sequence" (what do you mean by in sequence?)
Was there a large size difference among strains, even though they were the same age?
L140: With such a high infection pressure, I would be interested in some comments in the results section about their behaviour/activity levels during the 4-hour exposure period, and whether you had a feeling if there were strain differences in behavioural response.
L206: Was the ANOVA applied to pooled data across strains, or only for data within one strain (at a time)?
L215: Suggest to remove "repetition" and perhaps rephrase to something like "Challenge produced high variation in sea lice attachment among replicate tanks"
Section 3.2 - Can you present the fish weights, it does not seem to be obviously reported in the methods or results.
L234: I don't believe you mention the analysis in the Methods focusing on weight between strains? If you have done so, please rephrase so it is more obvious.
Author Response
Comment 1: This study presents a novel and interesting approach to understanding this host-parasite interaction. The hypotheses are well formulated, and the experimental design straightforward to adequately address the research question. I enjoyed reading the manuscript - it is eloquent but concise, and information is presented comprehensively whereby the details I was expecting were indeed mostly there. Although you do address the issue of large variation between tanks, I would have liked to see some discussion elaborating on why substantial differences were observed among replicate tanks, and how this influenced your conclusions. Otherwise, the discussion section adequately and concisely addressed a convoluted topic, so well done.
Response 1: We thank the reviewer for their comments. The reason we did not further elaborate on why substantial differences were observed among replicates is because we do not have a good hypothesis for why this is occurring, only that it consistently occurs. We have some future experiments planned that may expound on this, but at this time we prefer not to potentially add confusion to the discussion with unsupported speculation.
Comment 2: L25: For me, "challenge-specific" variability was unclear in terms of what measure you were referring to.
Response 2: We have changed “challenge-specific” to “tank-specific” to improve clarity.
Comment 3: L54-56: Perhaps revise sentence, particularly clarifying or rephrasing "preventing lice attachment simultaneously or in sequence" (what do you mean by in sequence?)
Response 3: We have clarified this text, which now reads “…lice management is now trending towards utilizing multiple strategies within an integrated pest management system that incorporates multiple strategies for preventing lice attachment either by parallel or series application [32].”
Comment 4: Was there a large size difference among strains, even though they were the same age?
Response 4: Yes. We have added text early in the methods section (Ln122-124) to clarify this, which now reads “Fish from all strains were obtained as eyed eggs at the same time and grown to approximately 20 months of age at the USDA-ARS National Cold Water Marine Aquaculture Center (NCWMAC) in Franklin, ME, USA. It should be noted that growth rates were highly variable between strains resulting in substantial size discrepancies by 20 months (e.g., SJR fish have been growth selected for over a decade and were approximately 2x mean body weight relative to GLS or CAS; Table S1).” We also discuss variability in strain specific growth rates leading to large variations in size between some fish later in the manuscript (Results Ln236-237 and Discussion Ln378-380).
Comment 5: L140: With such a high infection pressure, I would be interested in some comments in the results section about their behaviour/activity levels during the 4-hour exposure period, and whether you had a feeling if there were strain differences in behavioural response.
Response 5: After about 30 minutes post challenge fish exhibit behavior changes of increased flashing and jumping which lasted for approximately 1 hour and is typical for this challenge model in our experience. Unfortunately, the integrated transponder tags we used to individually identify fish in this experiment were internally located; thus, individual fish could not be visually identified as to which strain they belong to in situ. Although it could typically be presumed that the largest fish were SJR, this was not reliable enough and not applicable to differentiating CAS and GLS fish, so strain specific behavioral observations during challenge could not be obtained and were not recorded.
Comment 6: L206: Was the ANOVA applied to pooled data across strains, or only for data within one strain (at a time)?
Response 6: We have modified this sentence for clarity, which now reads “A two-way ANOVA was used to compare LC, LD1, and LD2 data between fish strains and challenge tanks (all data) followed by Tukey’s multiple comparison tests to determine differences between fish strains within each challenge replicate.”
Comment 7: L215: Suggest to remove "repetition" and perhaps rephrase to something like "Challenge produced high variation in sea lice attachment among replicate tanks"
Response 7: We accept the suggested change by the reviewer. The title for this section now reads “Challenge produced high variation in sea lice attachment among replicate tanks”
Comment 8: Section 3.2 - Can you present the fish weights, it does not seem to be obviously reported in the methods or results.
Response 8: We have added to text to Ln 249 to indicate all fish weights are provided in Table S1, which now reads “All individual fish weights are provided in Table S1.”
Comment 9: L234: I don't believe you mention the analysis in the Methods focusing on weight between strains? If you have done so, please rephrase so it is more obvious.
Response 9: We have added text early in the methods section (Ln122-124) to clarify this, which now reads “Fish from all strains were obtained as eyed eggs at the same time and grown to approximately 20 months of age at the USDA-ARS National Cold Water Marine Aquaculture Center (NCWMAC) in Franklin, ME, USA. It should be noted that growth rates were highly variable between strains resulting in substantial size discrepancies by 20 months (e.g., SJR fish have been growth selected for over a decade and were approximately 2x mean body weight relative to GLS or CAS; Table S1).” We also discuss variability in strain specific growth rates leading to large variations in size between some fish later in the manuscript (Results Ln236-237 and Discussion Ln378-380).
Reviewer 2 Report
Comments and Suggestions for AuthorsA very interesting view on the Copepodid Sea Lice Attachment with even more interesting
results, applicable in artificial farming of Atlantic salmon
The authors quite rightly suggest further study of parasite-host interactions, especially a broader
view of the context of the two in the environment.
It would be useful to add the time span of the experiment.
Author Response
Comments 1: A very interesting view on the Copepodid Sea Lice Attachment with even more interesting results, applicable in artificial farming of Atlantic salmon. The authors quite rightly suggest further study of parasite-host interactions, especially a broader view of the context of the two in the environment. It would be useful to add the time span of the experiment.
Response 1: We thank the reviewer for their comments. Although we provide the experimental duration on Ln145-146 “Lice were allowed to develop for 7-10 days post infestation (dpi) to the second chalimus stage, after which fish were euthanized with an overdose of MS-222”, we have added additional text to Ln164 to provide a second mention of this for additional clarity. This section now reads “Lice count (LC) per fish at 7-10 dpi was recorded and further standardized to body weight (BW) by two different methods.”
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript provides valuable insights into the differential susceptibility of three salmon strains to sea lice infections. The study is well-structured, the methods are described in sufficient detail for replication, and the results are clearly presented with effective supporting figures. I have no major concerns but offer a few minor suggestions:
Abstract
Lines 15 – 18- Check redaction (“Although lice counts… was similar between strains.”). It seems that sentence could be rephrased for better clarity.
Methods
Line 123. If all fish were the same age, why weights ranging from 104 – 453 g (line 167)?
Line 206. ANOVA?
Discussion
Consider adding a short paragraph on study limitations. Suggest future improvements.
Author Response
Comment 1: Lines 15 – 18- Check redaction (“Although lice counts… was similar between strains.”). It seems that sentence could be rephrased for better clarity.
Response 1: We thank the reviewer for their comments. We have rephrased this sentence and split it into two sentences for better clarity. This section now reads “Lice counts were correlated with body size and highest on St. John River (SJR; open ocean-run) relative to Grand Lakes Stream (GLS; 200-year restricted ocean-run) or Sebago Lake (CAS; ~11,000 year landlocked) Atlantic salmon. However, lice density was similar between strains.”
Comment 2: Line 123. If all fish were the same age, why weights ranging from 104 – 453 g (line 167)?
Response 2: We have added text early in the methods section (Ln122-124) to clarify this, which now reads “Fish from all strains were obtained as eyed eggs at the same time and grown to approximately 20 months of age at the USDA-ARS National Cold Water Marine Aquaculture Center (NCWMAC) in Franklin, ME, USA. It should be noted that growth rates were highly variable between strains resulting in substantial size discrepancies by 20 months (e.g., SJR fish have been growth selected for over a decade and were approximately 2x mean body weight relative to GLS or CAS; Table S1).” We also discuss variability in strain specific growth rates leading to large variations in size between some fish later in the manuscript (Results Ln236-237 and Discussion Ln378-380).
Comment 3: Line 206. ANOVA?
Response 3: ANVOA has been corrected to ANOVA.
Comment 4: Consider adding a short paragraph on study limitations. Suggest future improvements.
Response 4: We have carefully reviewed our Discussion section and believe that the study limitations have been generally presented (e.g., identifying high tank-to-tank challenge variation and the confounding factor for host size in identifying age-matched strain specific settlement), particularly in the concluding paragraph (Ln372-385). However, if the reviewer has a specific limitation they are thinking of that we have not addressed, we would be open to adding text to address it.
