Effects of Constant Water Flow on Endurance Swimming and Fatigue Metabolism of Large Yellow Croaker

Round 1

Reviewer 1 Report

 

The manuscript by Chai et al., describes a study of Yellow Croaker swimming ability and associated fuel resources designed to inform marine aquaculture efforts.  The authors used an innovative swim tunnel approach to measure endurance and preferred swimming speeds and measured muscle/liver glycogen, glucagon, and muscle/blood lactate levels at different time points of sustained swimming.   

Overall, this is an interesting study that should aid investigators in marine aquaculture.  However, there are numerous grammatical errors throughout and many of the sections are not presented clearly.  Thus, I recommend that the manuscript undergo major revision before it can be considered for publication.

Specific Comments:

Lines 44-45:  Unclear how hindering swimming would lead to swimming fatigue.  I think maybe the authors mean something like “imposes exhaustive swimming due to strong currents” or something similar instead of “hinders swimming”.

Line 48:  critical swimming speed and maximum sustained swimming speed are the same thing

Line 52-53:  suggest removing “(30 min)” here as this is not fixed and I would argue is less common than the more typical 20 min interval.  Also, suggest changing the text that follows to “at increasing flow rates of defined increments (typically 0.5 body lengths per second).”  Not sure why growth rate is included in this sentence.  Also, the second part of this sentence (after the semicolon) needs a reference.

Line 71:  please define BL (body length) on first use.

Lines 72-73:  presenting absolute swim speed (i.e., in cm/s) provides little support to this statement since it is dependent on the length of the fish (e.g., a small zebrafish swimming at this speed would not be considered a weak swimmer) – suggest converting to BL/s if possible; also, please italicize genus and species of fishes throughout the manuscript. 

Line 93:  a single tank?  What was the volume of the tank and water?

Section 2.3:  please clarify if the 64 fish were tested individually or as a group – this is clarified later, but should also be clear here.  What is the resolution/accuracy in choosing a preferred swimming speed when using so many fish simultaneously?  How is location used to determine flow speed?  The authors only mention measuring flow with a flow meter for section G.  I assume fish were placed in a different tank after testing so that the same fish was not used in more than one trial?

Line 137:  320 tails?  What are the tails in reference to?  Also, the authors stated there were only 300 fish previously (see line 92). 

Lines 147-148:  these 2 sentences describe different flow rates for some reason and the first is in BL/s whereas the others are in m/s.

Line 152:  here and throughout, suggest “habituation” or “acclimation” instead of “adaptation” as the latter refers to gene flow within a population over many generations.

Line 156:  5 times per fish?

Table 1:  please remove or modify first sentence of footnote since no differences are indicated

Line 165:  why was 0.35 m/s selected?

Line 170:  I think the authors mean i.e., instead of e.g., here.

Line 172:  were the fish euthanized prior to these steps?

Lines 204-208:  this is rather confusing as presented.  Are the swim times predefined for these tests?  It seems that way as written.  It would seem to make more sense that at the given swimming speeds the swimming times were measured, but the way this is presented makes it sound like the opposite. 

Figure 4:  please include flow rate in figure caption

Table 2:  the footnote shows mean+/-SEM, but only 95% CI’s are presented.  Why show CI’s and not mean +/- SE here?

Line 247:  lysis?

Line 289:  Presumably?  I would think this would not have to be presumed.

Line 296:  please delete “is”

Line 317:  I think the authors mean shape instead of size here; also there are many fish with laterally compressed bodies that are fast streamlined swimmers, so I don’t think that contributes to weak swimming ability

Line 331:  I don’t believe this can be broadly applied to all fish as indicated in this sentence

Lines 334-335:  I think the authors mean glycogenolysis instead of glycolysis here

Lines 334-335:  unclear what is meant by “dynamic diffusion or mutual transformation relationship.”

Lines 348-349:  not sure the data necessarily supports this, and why this connection would need to be invoked seems odd.

Lines 376-378:  the authors measured muscle lactic acid, so unclear what is meant here.

Section 4.4:  this section is not written clearly and should be revised extensively.  For example, Lines 385-386 are very odd as written – it is not valid to consider liver glycogen as an energy-supply substance?  And is lower than fat and muscle?  I think the authors mean that glucose does not provide as much energy as lipids on a molar basis and that muscle glycogen may be more important in this context than liver glycogen, but that is not how it is presented.  The rest of the section also need careful attention and revision.  Most importantly, please discuss why measuring these biochemical parameters are informative for your aquaculture approach.  What are the implications of this data for improving aquaculture?

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The goal of this study was to characterize the swimming capabilities of yellow croaker to help inform procedures for marine-based aquaculture of this species. Three experiments were run: 1) a free-choice flow rate experiment to estimate preferred swim rate of schooling fish, 2) an endurance test at set rates of single fish contained in a cage, and 3) measurement of metabolic markers at set times from fish forced to swim at an intermediate level (0.35 m/s) for 150 minutes. A generalized linear model is presented for prediction of supported flow rates using glucagon and hepatic glycogen as the primary factors. Overall, this is a well-designed study that is supported by appropriate references to the literature. The conclusions drawn are reasonable interpretations of the presented results.

General comments

Table 1 – I cannot find a reference to this Table in the text. This table is a bit confusing, because if I understand correctly, the “swimming time” header is actually the observed experimental data. This information should be reorganized. How was “plumpness” computed? It would probably be better to use a more standardized metric such as Fulton’s condition factor instead.

Figure 2 – Include information in the legend indicating what is shown in each of the five panels. The information provided in the text gives the meaning of these results, but the figure itself is not well described.

Line 386 – I disagree that the lower energy content invalidates this idea. The results presented here for yellow croaker indicate that liver glycogen is an important factor, and its depletion may be able to be used to indicate reduced swimming ability. This seems to support the argument made previously for redfish, at the least that this may be preferentially utilized for energy prior to the more energy-rich substrates or fat and muscle.

Specific comments

Line 50 – I’m not sure what is meant by “lower transportation cost”

Line 52 – “fixed flow rate growth rate” – I think you mean the increment pace, rather than growth of the fish, but suggest rephrasing for clarity

Line 100, lines 172-173 – the same dose of eugenol was used for both anesthesia and euthanization? This would suggest a very slow procedure and difficulty in determining point of death. Were blood and tissue samples for the metabolic indicators taken from sedated fish, or post-mortem?

Line 148-149 – It is stated that the flow rate is 2.64 BL/s, but then gives the 6 tested rates. If the fish did not differ in size, how was this accomplished?

Line 212 – Because the absolute and relative swimming speeds are presented independently, this figure does not actually give any information about the relationship between them. Rephrase the legend for this figure.

Line 247 – delete “lysis”

Line 268 – specify that this is hepatic glycogen

Lines 294, 299 – make sure that Latin names are italicized throughout the manuscript

Line 358 – I’m not sure what “controversy” is referred to here. Perhaps just poor word choice?

Line 370 – This reference should be to Figure 4.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I thank the authors for kindly addressing my concerns.  I only have some minor additional comments below:

Lines 52-53:  there is no reason to include “the flow rate growth law” for a description of Ucrit

Line 95:  please include units for length, etc.

Line 133:  what is the “A” in reference to?  Do the authors mean “R”?  Did the authors derive this equation or should there be a citation here?

Lines 414-417:  unclear why the authors are referring to data as being “reliable” or not here.  If the data is not reliable, then it should not be published.  Perhaps the authors are trying to make a different point here, but if so, this needs to be carefully reworded.    

Author Response

Please see the attachment.

Author Response File: Author Response.pdf