Unexpected Discovery of an Ectoparasitic Invasion First Detected in the Baikal Coregonid Fish Population

Round 1

Reviewer 1 Report (New Reviewer)

I was honored to review the manuscript entitled “Sensational Discovery of an Ectoparasitic Invasion First Detected in the Baikal Coregonid Fish Population” submitted to Fishes journal. I would like to thank authors for preparing this research article in the good way. This study has a average quality and well written. However, it needs a few corrections for improving the quality. Here are some comments that I suggested:

1) Please add some data about clinical signs in introduction section.

2) Which methods of sequencing did you use? Sanger or illumina?

3) Line 370: Which viruses?

In conclusion, I believe that the present manuscript can be accepted after minor revision, for publication.

 

Author Response

Thank you for appreciating our work.

Below are the responses to your comments.

1) Please add some data about clinical signs in introduction section. -> There were not found any clinical signs concerning the case.

2) Which methods of sequencing did you use? Sanger or illumina? -> Amplicons of cox1 were used for Sanger sequencing. Information was added to Line 157.

3) Line 370: Which viruses? -> Viral hemorrhagic septicemia virus (VHSV) as described in the cited article [56].

Reviewer 2 Report (New Reviewer)

I really think that this study makes an interesting contribution, not only to the knowledge of the parasite fauna in a commercial fish species, but specifically of this group of fish parasites, the Hirudinea. I only miss better and more detailed photographs of the parasite. Would this be possible?

With regard to the title, I am not an English native, but I found the title somewhat strange. I do not understand the adjective “sensational” in that context, even the fact of giving that adjective as part of a scientific paper title. Maybe for a divulgative or an informative text for a wider audience it would fit better. Moreover, you may consider changing the word discovery, as I also find strange the idea of discovering a living organism.

The statement in the abstract (Lines 9, 10 and 11): The omul, Coregonus migratorius (Georgi, 1775), being an endemic fish to Lake Baikal, is nevertheless the main commercial species of essential economic importance for the extensive region in Eastern Siberia seems to me contradictory with the sentence “there is a ban on its commercial catch and amateur fishing (from 2017)” (lines 32 and 33). If commercial catch is banned from 2017, how can be now the main commercial species?

Also, in the abstract (lines 11-14) you emphasize the fact that nobody have mentioned that parasites in this fish species. Nevertheless, as you have mentioned in the discussion section, you have had a unique opportunity to conduct these studies, as you have obtained samples of spawning individuals, something that have been possible only for the very special circumstances of obtaining a very good sample of an illegal catch. Also, the high number of individuals analysed (633) have allowed to detect leeches despite their low prevalence.

Line 175: intensity or main intensity? I have read the reference (number 43), and I think that you might consider using the reference of Bush et al. (1997) for the definition of those quantitative descriptors of parasitism [Parasitology Meets Ecology on Its Own Terms: Margolis et al. Revisited. Albert O. Bush, Kevin D. Lafferty, Jeffrey M. Lotz and Allen W. Shostak. The Journal of Parasitology Vol. 83, No. 4 (Aug., 1997), pp. 575-583 (9 pages)].

Line 375 and 376: I agree that information about this kind of ectoparasites is scarce. However, I do not think that this would be related to an underestimation of their importance and to the lack of proper attention by researchers. As you have stated in lines 214 to 216, leeches, as well as other ectoparasites, are generally underestimated because they are more fragile and easily detached from the host during fish capture. So, they are probably lost during routine parasitological examination.

 

Author Response

Thank you for high estimation of our job and professional discussion you suggested in your review.

Our reply please find in attached file.

Cordially,

IK on behalf of all authors

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This manuscript provided the first reliable information on the existence of specific annelid parasites infecting the pelagic population of Baikal omul, and presented possible scenarios for the leech infection of omul. The results indicated that the piscine leech may represent a potentially new species and genus, which needs to be monitored and controlled in the future.

 

Specific comments:

1.     A large part of the Introduction is devoted to describing the habits and population structure of the Baikal omul, while there is little information about the habits, infection condition and infection strategies of piscine parasites, especially the leeches.

2.     Line 96: “at the confluence of rivers the Ider and Delgermörön rivers”, delete the first “rivers”.

3.     Line 105: Check the spelling of “Central Pprotection Zone”.

4.     Line 233: “-20C” should be “-20℃”.

5.     Line 252-276: It is recommended that only the results obtained in this study be described in the Results section. The analysis and discussion of the results should be placed in the Discussion section.

6.     As mentioned, leeches have not been found in the continuous 250-year study of Baikal omul, but have recently been found! Why? Is it related to the emerging environmental changes mentioned in the first paragraph of Introduction? It is suggested to analyze the causes of the recent appearance of leeches in the Discussion section.

Author Response

Dear Reviewer!

Thank you for carefully reading our MS and suggestions for improving it.

All your comments were taken into account.

Find the answer to your specific comments in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript reports on the interesting finding of a leech presumably parasitizing on the Baikal coregonid, the omul, Coregonus migratorius. The authors claim this constitues  the first report of such an ectoparasitic annelid on the omul of Baikal lake; reported after many studies of this fish host. This finding is interesting and deserves fully attention. However, the manuscript lacks a number of necessary items and information. Which must be corrected before this Ms would be considered for publication.

1. A full morphological description of the leeches is needed. Including at least consideration of the next structures: papillae and lateral projections observed on dorsum of the leeches; eyespot; annulation on somites; longitudinal rows of papillae, longitudinal stripes, or any other observed metameric patterns; mouth position, presence/absence of jaws, denticles; testisacs; postion of the anus; relative size of the suckers. The brief lines (226-232) regarding the size of the leeches and the photos, Fig. 4 (even if we include lines 233-240) do not provide enough information to recognize any taxonomical diagnostic details of the reported specimens. Such that one is left without any support to accept it is a new record, a new species or even as authors suggest, a new genus. 

This morphological description would be compared in detail against the more similar Psicolid leeches as pictured in the Fig. 5 of the current Ms. Mainly a detailed comparison versus Caspiobdella fadejewi and the other leeches listed on current Table 3 is needed. Present comparisons (lines 252-276) are not morphological/morphometric comparisons, these rely on host-affinities. Do not provide any morphological sound comparison.

Authors suggest that these leeches are specific parasites, please revise this concept on the light of parasite specificity knowledge.

All of this is fundamental for this investigations, because as the authors recognized, there are scarce molecular data to improve the comparisons via molecular tools.

Vouchering of specimens is a must. Authors please deposit reference specimens in a well known permanent scientific collection, and provide the catalog numbers in the Ms.

 

2. Improve material and methods section. Give enough details about the procedence of the examined fishes (lines 133-135) All these fish were captured from the same location? on the same precise date? (October 2013?) what were the conditions of the captured fishes before the examination? did these specimens were captured/mixed with any other fish specimens from the same procedence? Authors please consider that 27/663 fish parasitized by just one ectoparasitic leech in frozen fish specimens at least cast doubts. Enough details must be given in order to disclaim this kind of pertinent doubts. (Lines 135-136 seem confused, one fish or 663 host examined?, please rewrite).

3. Focus the text on relevant data all throughout the Ms. For example, lines 179-194, 197-205 and Table 1 are not necessary taking in account the main goal of the manuscript. The same holds for lines 95-106: the whole paragraph (lines 95-131) needs to be focused on the main objective of the paper.

Author Response

Dear Reviewer,

Thank you for your work and valuable comments, which allowed us to see our material in a new way.

For a more detailed response to your comments, see the attached file.

Sincerely,

Authors

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Only minor (epidermical) changes were added to the Ms.

Not enough work.