First Evidence of Microplastic Contamination in Antarctic Fish (Actinopterygii, Perciformes)

Round 1

Reviewer 1 Report

The paper deals with a topic by now defined and which boasts numerous studies. The study is very basic and describes the presence of MP in the sampled fish without trying to investigate the causes or the relationships with the environment in which they live. The importance of the work lies in the study area which is little investigated. The methods used are those that are now standardized and effective. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, Zhang and co-workers have carried out the determination of microplastics in the digestive tract of species from five families of the order Perciformes from Antarctica. The MPs found were classified by sizes, shapes, colours and chemical composition. Although this work is of interest, as it is one of the few works published to date in which the presence of MPs in living organisms in remote areas such as Antarctica is evaluated, there are some aspects that must be corrected or clarified to consider its publication in the journal.

1)      More information on the treatment of samples should be given. How much time was required for the digestion of the samples? And for the separation of the MPs by flotation? Was it necessary to heat for digestion? Was the sample previously agitated? What type of agitation was applied? In addition, other questions arise, such as why the authors used KOH for the digestion and not H₂O₂. Why did they not evaluate this parameter?

2)      Regarding the control of contamination of the samples in the laboratory, did the authors use coloured lab coats to identify the fibres coming from them? Why were the samples not treated inside a glove box to reduce contamination of the laboratory environment? Where were the analyses of the samples carried out? How long were the samples frozen and what were the containers in which they were kept like? Were the fish externally washed before analysis to avoid contaminating the digestive tracts? It is very important to clarify these aspects.

3)      What do the authors want to say with “Given that the sample quantity in the RS did not meet the statistical requirements…”? This should be clarified, since one of the objectives of the work was the comparison of the results obtained between RS and AS. If the statistical analysis could not be done for one of the seas, this objective could not be achieved and, therefore, the work is incomplete.

4)      It is well known that one of the main limitations in determining MPs is precisely their size, since below certain dimensions, they cannot be visualized and even less classified based on their composition. Taking into account that the authors declare a maximum detection rate of 50%, it seems to indicate that they are underestimating the amount of MPs present in the fish. How do the authors explain this? Which is the limit of detection of this method?

Other specific comments:

-          The number of fish of each species that were analysed is not clear. This should be clearly specified in the text.

-          Better resolution figures should be provided.

-          It must be clearly specified how the health hazard risk was calculated.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The work is overall very interesting and represents an excellent baseline for future investigation. As it is the first work on MPs in Antarctic fish, it can be valued as more than sufficient.

The major concern regards the nature of the samples, which are composed by different species collected in the two areas. This could affect the comparison, since different species could have different feeding habits and could live in different habitats, which make them differently exposed to MPs. Even within the same family, species may have very different feeding modes (see for examples Carlig et al. 2018 'Diversification of feeding structures in three adult Antarctic nototheniis fish'). For this, to compare families may not be effective. 

Line 25 - here it is not clear how the potential 'unique gut microbiome' of the Artedidraconidae can affect the characteristics of the MPs that were found inside them

Line 40 - plastic degradation is not the only source of MPs, in some cases MPs are directly produced in the size at which they are found

Lines 61-63 - not all Antarctic Perciformes are benthic (for example, the pelagic Pleuragramma antarcticum, but there are also other non-benthic species); further, I suggest to change "such as the order Perciformes" to "such as most of those belonging to the order Perciformes" 

Line 64 - penguins are not mammals!

Line 69 - change "particularly dominant" to "particularly in dominant"

Line 72 - are they polymers or monomers?

Line 76 - change "benthic, mesopelagic" to "benthic and mesopelagic"

Line 81 - remove "In contrast,"

Line 90 - add "in the two areas" after the first "Perciformes"

Lines 95-98 - It may be interesting to add the bathymetry and possibly some environmental infomation to the coordinates

Line 114 - "physiological information" is too much generic, I suggest to specify what information was collected 

Lines 155-157 - normality was tested, in the requirements for the use of the ANOVA test there is also the homoscedasticity, which can be verified for example by meas of Levene's test

Line 161 - I suggest to specify better what is meant with "statistical requirements"

Table 1 - add SD to the average length of the species; it may also be worth to identify if the specimes are adult fish or juveniles, because during the life cycle diet, and then the exposure to MPs, could change

Line 177 - change "eight" with "ten"

Line 204 (and the whole pragraph 3.3) - is "family" the right level at which compare fishes? Different species belonging to the same family can have very different feeding methods, and then very different possibilities of interact with MPs

Line 205 - delete "orders"

Line 237 - H level should not be V if all MPs present have not such value of health risk level

Line 242 - delete "-and" after the word "Channichtyidae"

Line 243 - delete "And"

Line 247 - Antarctic fish are rarely a food source for humans; among the strictly Antarctic species, only Dissostichus mawsoni and to a lesser extent Champsocephalus gunnari - which are not among the analysed species - are fishing resources. For this, I suggest to delete the first phrase of the Discussion

Line 282 - change "COMMAP" with "COMNAP"

Lines 286-292 - there is to be more cautious with these conclusions, if species and environments are not the same, the comparison is not so logical

Line 335 - change "internationally" with "on a global scale"

Line 336 - it is not correct to say that the rate is "dramatically lower" if  no statistical difference was observed between the areas (as indicated in Line 188)

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

After reviewing the revised version of the manuscript, it can be seen that the authors have responded and clarified all the aspects indicated in the review of the first version, significantly improving its quality. Taking this into account, the manuscript can be considered for publication in the journal.