Fish Viscera Silage: Production, Characterization, and Digestibility of Nutrients and Energy for Tambaqui Juveniles

Round 1

Reviewer 1 Report

The paper “Fish viscera silage: production, characterization and digestibility 2 of nutrients and energy for tambaqui juveniles”, orepresents new information of great importance for the sustainability of aquaculture. However, essential information is missing to be able to reach certain conclusions mentioned by the authors.

Major comments

Essential methodological information is missing, as there is no clear description of the bioassay. It is mentioned that in 10 days the organisms acclimatized. In the same period, digestibility was determined.

To be sure that an organism has adapted to a diet, it must wait at least 2 to 3 weeks to make a decision (changes in the microbiota and other physiological processes).

Why are the performance and health indices of the organisms not mentioned in the results?

In the same way, 10 days is a very short time to know if an ingredient works  as an energy source in organisms (as the title of the research says).

Minor comments

-In table 1, add the treatments and inclusion levels on each of the diets (treatments), and join table 1 and 2 (by convention the formulations and proximal analysis usually go together).

-Table 4 Myristic with a capital letter

-You mean that the duration of the reaction is 16 hours, not that it was at 4 pm, right?

Author Response

Reviewer 1

The paper “Fish viscera silage: production, characterization and digestibility of nutrients and energy for tambaqui juveniles”, represents new information of great importance for the sustainability of aquaculture. However, essential information is missing to be able to reach certain conclusions mentioned by the authors.

Major comments

1.Essential methodological information is missing, as there is no clear description of the bioassay. It is mentioned that in 10 days the organisms acclimatized. In the same period, digestibility was determined.

We apologize to the reviewers. There was information missing from the methodology section. Fish were acclimated to laboratory conditions for 10 days. After the acclimatation period, fish feces were collected once a day for 21 days (time required to have enough feces sample for laboratory analysis). We added the information in methodology section.

2.To be sure that an organism has adapted to a diet, it must wait at least 2 to 3 weeks to make a decision (changes in the microbiota and other physiological processes).

Why are the performance and health indices of the organisms not mentioned in the results?

The apparent digestibility assay is used to quantify the “amount or proportion of nutrients or categories of nutrients, such as protein, that disappears from a meal as it passes through the digestive system and is excreted (egested) in feces” (NRC, 2010).

The indirect method of digestibility determination is widely used with most species of farmed fish.  We present in this manuscript an experiment of apparent digestibility of nutrients and energy from silages. We would like to make it clear that the digestibility assay is not related to the assessment of growth performance and health indices. There are several articles published only with the digestibility assay for fish, when evaluating a potential ingredient for fish diets, as you can see in these examples:

Fontes, T. V., de Oliveira, K. R. B., Gomes Almeida, I. L., Orlando, T. M., Rodrigues, P. B., da Costa, D. V., & Rosa, P. V. E. (2019). Digestibility of insect meals for Nile tilapia fingerlings. Animals, 9(4), 181.

Köprücü, K., & Özdemir, Y. (2005). Apparent digestibility of selected feed ingredients for Nile tilapia (Oreochromis niloticus). Aquaculture, 250(1-2), 308-316.

Mmanda, F. P., Lindberg, J. E., Norman Haldén, A., Mtolera, M. S., Kitula, R., & Lundh, T. (2020). Digestibility of local feed ingredients in tilapia Oreochromis niloticus juveniles, determined on faeces collected by siphoning or stripping. Fishes, 5(4), 32.

Gong, Y., Guterres, H. A. D. S., Huntley, M., Sørensen, M., & Kiron, V. (2018). Digestibility of the defatted microalgae Nannochloropsis sp. and Desmodesmus sp. when fed to A tlantic salmon, Salmo salar. Aquaculture Nutrition, 24(1), 56-64.

In the same way, 10 days is a very short time to know if an ingredient works as an energy source in organisms (as the title of the research says).

We apologize to the reviewers. There was information missing from the methodology section. Fish were acclimated to laboratory conditions for 10 days. After the acclimatation period, fish feces was collected once a day for 21 days (time required to have enough feces sample for laboratory analysis). We added the information in methodology section.

The indirect method of digestibility determination is widely used with most species of farmed fish to evaluate the nutrient and energy availability of a potencial ingredient, as you can see in these examples:

Meurer F, Franzen A, Piovesan P, Rossato KA, Santos LD. Apparent energy digestibility of glycerol from biodiesel production for Nile tilapia (Oreochromis niloticus, Linnaeus 1758). Aquaculture Research. 2012 Oct;43(11):1734-7.

Mzengereza K, Singini W, Msiska OV, Kapute F, Kang’ombe J, et al. (2016) Apparent Nutrient Digestibility of Plant Based Diets by Tilapia rendalli (Boulenger, 1896). J Aquac Res Development 7: 396.

Minor comments

1. In table 1, add the treatments and inclusion levels on each of the diets (treatments), and join table 1 and 2 (by convention the formulations and proximal analysis usually go together).

Thank you for your suggestion. We added the treatments, and the silage inclusion levels on each experimental diet (Table 1). However, we would like to explain that the proximate composition of Table 1 refers to experimental diets, and proximate composition of Table 2 refers to silage. Therefore, the tables remain separated.

2. Table 4 Myristic with a capital letter

Thank you for your correction. The text was modified accordingly.

3. You mean that the duration of the reaction is 16 hours, not that it was at 4 pm, right?

Thank you for your correction. The duration of the reaction was 16 hours. It was corrected in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

As in other productive sectors, aquaculture requires changes in traditional patterns of action in order to remain sustainable. Among the most affected aspects in this regard is the preparation of diets, burdened by the increasing scarcity and high costs of fishmeal, the protein substrate mostly used for this purpose. The search for alternative sources that have a positive impact on production costs, do not cause negative environmental impact and are accepted by fish, without affecting productivity and organoleptic properties, is the aquaculture industry's main objective. The present work is framed in this scenario, showing an interesting alternative and adjusted to the current requirements of the circular economy. And although the study does not show the level of depth that would be desirable, it can be considered as a first necessary step to advance in proposals that allow the establishment of new feeds.

Sugerencias menores

-Aunque no hay grandes errores, el texto necesitaaría ser revisado en su redacción. Especialmente en la utilización de signos de puntuación, ya que a causa de su mal uso (ausencia) determinadas frases pierden el sentido o resultan difíciles de entender (L. 30-33; L. 106-107).

-Todos los nombres científicos deben ir en cursiva.

-El pie de la Figura 2 no explica los gráficos. Indique lo que representan A, B, C y D.

Author Response

Reviewer 2

As in other productive sectors, aquaculture requires changes in traditional patterns of action in order to remain sustainable. Among the most affected aspects in this regard is the preparation of diets, burdened by the increasing scarcity and high costs of fishmeal, the protein substrate mostly used for this purpose. The search for alternative sources that have a positive impact on production costs, do not cause negative environmental impact and are accepted by fish, without affecting productivity and organoleptic properties, is the aquaculture industry's main objective. The present work is framed in this scenario, showing an interesting alternative and adjusted to the current requirements of the circular economy. And although the study does not show the level of depth that would be desirable, it can be considered as a first necessary step to advance in proposals that allow the establishment of new feeds.

Sugerencias menores

1. Aunque no hay grandes errores, el texto necesitaaría ser revisado en su redacción. Especialmente en la utilización de signos de puntuación, ya que a causa de su mal uso (ausencia) determinadas frases pierden el sentido o resultan difíciles de entender (L. 30-33; L. 106-107).

Thank you for your suggestion. The text was modified accordingly.

2.Todos los nombres científicos deben ir en cursiva.

Thank you for your correction. The text was modified accordingly.

3. El pie de la Figura 2 no explica los gráficos. Indique lo que representan A, B, C y D.

Thank you for your suggestion. The text was added as requested.