Hermetia illucens for Replacing Fishmeal in Aquafeeds: Effects on Fish Growth Performance, Intestinal Morphology, and Gene Expression in the Zebrafish (Danio rerio) Model

Round 1

Reviewer 1 Report

The experiment has been well designed and conducted. The results are also well presented and discussed.  The references may be made uniform as per the journal style. This is an excellent piece of work.

Author Response

We are glad for the positive feedback and the kind words about our work. In relation to the references, we used the Reference Manager tools set for the MDPI format. However, we manually checked for possible not standardized citations and listed papers.

Author Response File: Author Response.pdf

Reviewer 2 Report

 

Insect meal has been considered as the alternative protein source for replacing fishmeal in aquafeeds. This study explored the effects of dietary Hermetia illucens on the growth performance, intestinal morphology, and gene expression of zebrafish. Overall, the design of this study is sound, and the results are reliable. This study has presented some interesting results and could benefit the industries. After revision, this manuscript can be considered for publication.

 

Some specific comments:

In the experimental design, why use 50% fishmeal as the control? Is it a common inclusion amount?

Lines 225-226: please add “P > 0.05” after “the experimental periods”.

 

Lines 295-297: please rewrite this sentence, as the current statement may mislead the readers.

Lines 297-310: although authors tried to compare their data with previous findings, the conclusion of their results was missing. Why FCR was lower in dietary treatments still needs to be explained clearly.

Lines 323-325: please focus on freshwater species. The case used here is incomparable.

Author Response

We are glad for the positive feedback and the kind words about our work and below we answer to the reviewer comments, point by point.

Answer to comment 1) The reason of including fishmeal up to a rate of 50% is mainly that in a previous study (Fronte et al., 2021), where 20% fishmeal inclusion was compared with 20% insect meal feed inclusion, no differences where observed. For a contrary, other authors referred that differences were observed when insect meal was included at higher rates (e.g., 33%; Kroekel 2012).

Therefore, in the present study we decide to investigate whether the fishmeal total replacement with insect meal might be possible without negative impact on growth performances also when the two raw materials were used at higher level (e.g., 50% inclusion, with 100% replacement rate).

Despite including 50% fishmeal in aquafeeds may appear nowadays quite uncommon, this was pretty common up to few decades ago, when fishmeal was commonly included up to 60-65% in feeds for carnivores species such as Salmon, Gilthead Seabream, European Seabass and Turbot.

Definitely, the paper won’t suggest including fishmeal or insect meal at this level, but just highlight that in case of need or future economical convenience, it might be considered.

Answer to comment 2) done. Thank you

Answer to comment 3): done. The sentence was modified as follow: “On the contrary, FCR was significantly more favorable when Hermetia illucens meal was included even at the higher level, and totally replacing fishmeal.” Thank you

Answer to comment 4): thanks for the suggestion, really worthy. To follow the reviewer suggestion, at the end of the paragraph we added the following sentence: “In the lack of specific studies, this result can be hypothetically explained based on the dietary differences and notably with the slightly higher crude lipid content and lower fibre, starch and ash content in the diet containing HI meal. Similarly, another hypothesis might be related to the dietary ammino acids profile, notably for Lysine and Methionine and Cysteine, among others (Table 1).” Hopefully it helps.

Answer to comment 5) In the present study, zebrafish (freshwater species) is used as a teleost model, hence for both freshwater and marine fish. In fact, the results observed were frequently consistent with those reported by other authors for both freshwater and marine water fish. However, in this case the mentioned species is a crustacean and even thought the case refers to the use of insect meal, it may be deleted without losing any significant content. Hence, we decide to follow the referee suggestion deleting the paragraph.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an interesting multidisciplinary investigation on a relevant topic on the future directions to be taken in fish feeding taking into consideration the need to replace animal protein with origin in fish. Overall,  the paper reads well and is adequately organized in the correct sections.

I suggest that keywords might include the Latin name of the species considered in this study replacing the common-name.

The Introduction provides a good state-of-the-art, supported by the relevant references and the objectives of this investigation are clearly described.

The methods are adequate, the  experimental protocol is well described and considers enough replicates. The statistical analysis is adequate.

The results are clearly presented and the Discussion provides a good interpretation and integration of these results.

I understand that this is an experimental/laboratory approach on the use of insects as protein source for fish feeding and this might work for use on biological models as zebra-fish and other small-size species where the amount of food to supply is relatively low (at least, when compared to fish production in industrial aquaculture). The prospects for future use under an industrial level and or large-scale production might (should be?) considered with care and some reference to this might be added in the last paragraph of the Conclusions. 

Author Response

Answer to comment 1) Done. Thank you.

Answer to comment 2) Thank you.

Answer to comment 3) Thank you.

Answer to comment 4) Thank you.

Answer to comment 5) Thank you for the comment. We guess the referee refers to the high market price of insect meal which is not an economically convenient alternative to fishmeal. In this case, we totally agree with that and as suggested by the reviewer we added the following sentence together to a reference citation, in the manuscript: “In turn, it is necessary to consider its high market price, that nowadays is not yet economically competitive with fishmeal but, in the perspective of the increasing demand for seafood, the fishmeal market shortage, the increasing insect meal production, and the needs of improving aquaculture “sustainability”, insect meal possess all the required characteristics to become a convenient alternative to fishmeal for aquafeed production”.

Author Response File: Author Response.pdf