Tambaqui Production at Different Stocking Densities in RAS: Growth and Physiology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper was very well written and I understood exactly the statistics that were used, which were used correctly. This paper is one that I would consider as a major reference because when I worked with tambaqui, I could not find a paper like this, even though the tambaqui is as popular as it is in Brazil. 

Author Response

Reviewer 1

Comments and Suggestions for Authors

This paper was very well written and I understood exactly the statistics that were used, which were used correctly. This paper is one that I would consider as a major reference because when I worked with tambaqui, I could not find a paper like this, even though the tambaqui is as popular as it is in Brazil. 

Dear reviewer, we appreciate your comments and compliments on our work.

Reviewer 2 Report

Comments and Suggestions for Authors

Colossoma macropomum, also known as the tambaqui or black pacu, is a species of freshwater fish native to the Amazon River basin in South America. It is a large fish, with a maximum recorded length of over 1 meter and a weight of up to 40 kilograms. Tambaqui are popular in aquaculture due to their fast growth rate and high-quality meat. They are omnivorous, feeding on a variety of plant material, fruits, and small animals. In the wild, they play an important role in seed dispersal and nutrient cycling in the Amazon rainforest. This study evaluated the production of juvenile Colossoma macropomum at different stocking densities in a recirculating aquaculture system. The objective of this study is critical for field practices, results from this study will guild the field aquaculture. Overall, the design of this study is sound, and the results are reliable. After revision, this manuscript can be considered for publication in fishes.

 

Comments should be addressed in the revision:

1.     Why experiment 1 lasted only 15 days? Please justify the reason in the revised manuscript.

2.     The recirculating aquaculture system used in this study should be described in details, as for field practices experiment, such information is important.

3.     In the conclusion, the authors mentioned: lower densities achieved greater weight gain, but higher densities achieved greater biomass. For field practices, any suggestions?

Author Response

Reviewer 2

Comments and Suggestions for Authors

Colossoma macropomum, also known as the tambaqui or black pacu, is a species of freshwater fish native to the Amazon River basin in South America. It is a large fish, with a maximum recorded length of over 1 meter and a weight of up to 40 kilograms. Tambaqui are popular in aquaculture due to their fast growth rate and high-quality meat. They are omnivorous, feeding on a variety of plant material, fruits, and small animals. In the wild, they play an important role in seed dispersal and nutrient cycling in the Amazon rainforest. This study evaluated the production of juvenile Colossoma macropomum at different stocking densities in a recirculating aquaculture system. The objective of this study is critical for field practices, results from this study will guild the field aquaculture. Overall, the design of this study is sound, and the results are reliable. After revision, this manuscript can be considered for publication in fishes.

 

Comments should be addressed in the revision:

1. Why experiment 1 lasted only 15 days? Please justify the reason in the revised manuscript.

The rapid growth of the fish during the 15 days of experiment 1 resulted in an increase in ammonia in the RAS system, making it necessary to close it to reduce the stocking density and thus start the second experiment.

2. The recirculating aquaculture system used in this study should be described in details, as for field practices experiment, such information is important.

Blue circular polyethylene tanks were used with dimensions of 115 x 115 x 76 cm, total volume of 1 m³ and 0.8 m³ of useful volume, connected to an individual 80 L biological filter, where crushed stone was used as substrate, and a mechanical filter made with acrylic wool, changed weekly. The water outlet was positioned on the lower side of each tank, and the inlet was positioned on the upper side connected to the “air-lift” aeration system. Each tank received supplementary aeration and had an individual heating system, using an 200-watt heater. Following the scheme made by Santos et al., 2021 (10.1016/j.aquaculture.2020.736274).

3. In the conclusion, the authors mentioned: lower densities achieved greater weight gain, but higher densities achieved greater biomass. For field practices, any suggestions?

Dear reviewer, Thank you for your comment. In practice we need to do an economic analysis. However, the choice to produce a smaller quantity of heavier animals, or a greater biomass of smaller fish depends on the producer's objective. The species C. macropomum can be sold in different sizes and shapes, such as directly for slaughter or for rearing and even ornamentation. Therefore, a producer whose objective is to produce during the rearing phase, can opt for a higher stocking density, rather than obtaining heavier animals individually.

Reviewer 3 Report

Comments and Suggestions for Authors

Abstract

Ln. 10: Replace “cultivation” (here and anywhere else) with “reared” or “farmed”, since Colossoma macropomum is a fish species and not a plant species.

 

Introduction

The section is concise and adequate.

 

Materials and Methods

Ln. 73: Provide more details regarding tanks used, i.e. dimensions, material of construction, colour, water inlet and water outlet position.

Ln. 154-155: Five fish from each tank leads to a different percentage of fish sampled per tank. It would be better to obtain e.g. a 10% of each fish group. Please justify the adequacy of fish samples.

Ln. 160-161: Total protein is usually measured colorimetrically. Since I have not heard before such a measurement for total protein, please add references for the validation of the method. Otherwise, please remove the analysis/results/discussion from the manuscript.

Ln. 183-186: It is not clear, either here or in Tables which was considered the experimental unit for statistical analysis (n=??). This is very important to be stated since, if it not correct, then statistics should be repeated.

Water exchange rate: the only information provided is reported for Experiment 1 in ln. 75. What was the water exchange rate for the other two experiments?

 

Results

Table 2: A significant difference (P=0.0132) is also shown for DWG (g/day) but it is ignored by the authors. Please correct accordingly.

Standard deviations: Since it is not clear what was considered as the experimental unit (see comment for ln. 183-186), it is also not clear what variability these reported standard deviations represent.

Table 2 and 3: FCR reported are too good ! Please recheck data and calculations and adjust relative discussion parts.

Tables 2, 3, 6: The report of absolute food consumption (i.e. Kg) is not informative and is not correct for differently sized fish. Please express and report feed consumption as % of body weight and then repeat statistics. It is the only way to compare experimental treatments on a common basis.

Table 6: Standard deviations for parameters in D2 are very high. Why?

Table 6: Recheck FCR, since it is very strange that a value of 2.36 (D2) does not differ from a value of 1.36 (D6).

 

Discussion

Ln. 301-302: Italics for the scientific name.

Ln. 314: It would be useful to add fish/L for the present experimental treatments in Tables.

Ln. 319-327 (and major conclusion): Although I understand the authors’ point of view, productivity in aquaculture is not only “produced biomass”. Instead, final weight together with feed efficiency (FCR) and food consumption (as % body weight) are among the most important indices. Present results showed that increasing density resulted in lower final weight (Experiments 2 and 3) with better feed efficiency (not significantly different but lower values in Experiments 2 and 3). This is quite contradictory! Obviously, some involvement of feed consumption is indicated. However, unless feed consumption is expressed as % of body weight, the evaluation of productivity is incomplete. I strongly suggest the re-evaluation of results (and relative discussion) after the correct expression of feed consumption.

Author Response

Comments and Suggestions for Authors

Abstract

Ln. 10: Replace “cultivation” (here and anywhere else) with “reared” or “farmed”, since Colossoma macropomum is a fish species and not a plant species.

Dear reviewer, we thank you for the suggestion and the term “cultivation” was replaced by “reared”.

Introduction

The section is concise and adequate.

 Materials and Methods

Ln. 73: Provide more details regarding tanks used, i.e. dimensions, material of construction, colour, water inlet and water outlet position.

Blue circular polyethylene tanks were used with dimensions of 115 x 115 x 76 cm, total volume of 1 m³ and 0.8 m³ of useful volume, connected to an individual 80 L biological filter, where crushed stone was used as substrate, and a mechanical filter made with acrylic wool, changed weekly. The water outlet was positioned on the lower side of each tank, and the inlet was positioned on the upper side connected to the “air-lift” aeration system. Each tank received supplementary aeration and had an individual heating system, using an 200-watt heater.

Ln. 154-155: Five fish from each tank leads to a different percentage of fish sampled per tank. It would be better to obtain e.g. a 10% of each fish group. Please justify the adequacy of fish samples.

The number of animals for blood and somatic indices analyzes were previously submitted to the Ethics Committee on the Use of Animals, where a calculation was presented to determine the sample n that would allow the veracity of the data with a reduced number of animals subjected to harmful handling. to their well-being such as blood collection and euthanasia. Furthermore, the present study was based on the results obtained by Santos et al., (2021) (10.1016/j.aquaculture.2020.736274), where a sample size of 5 fish per tank was used.

Ln. 160-161: Total protein is usually measured colorimetrically. Since I have not heard before such a measurement for total protein, please add references for the validation of the method. Otherwise, please remove the analysis/results/discussion from the manuscript.

The method used to analyze plasma protein levels using a portable refractometer that consists of removing plasma from the capillary tube after reading the microhematocrit and was used in several studies with fish (10.1016/j.aquaculture.2021.737583; 10.1016/j .aquaculture.2022.738161; 10.3390/agriculture12071025;10.1007/s10695-022-01109-w; 10.1007/s10695-020-00900-x). COLOCAR MAIS ARTIGOS

Ln. 183-186: It is not clear, either here or in Tables which was considered the experimental unit for statistical analysis (n=??). This is very important to be stated since, if it not correct, then statistics should be repeated.

For the zootechnical performance variables, all fish were sampled through biometric management. For hematological, biochemical analyzes and calculations of vicerosomatic, hepatosomatic and visceral fat indices, 5 animals/tank were used, totaling 15 fish/treatment as shown in the calculations in the previous suggestion.

Water exchange rate: the only information provided is reported for Experiment 1 in ln. 75. What was the water exchange rate for the other two experiments?

Water exchange management was carried out as follows: during the first experiment, no water exchange was carried out. In the second experiment, during the first 21 days there was no water change, between days 22 and 28 of the experiment, 10% of the volume of each tank was changed once a week; Between days 29 and 56, 10% of each tank was changed twice a week and from day 57 until the end of the experiment, 20% of the volume was changed three times a day. During the first 30 days of experiment 3, no water changes were made; between days 31 and 45, 10% of the volume was changed once a week; between days 46 and 60, 10% of the volume was changed twice a week. and from day 61 until the end of experiment 3, 20% of the volume was changed three times a week.

These statements were added to the material and methods of each experiment.

Results

Table 2: A significant difference (P=0.0132) is also shown for DWG (g/day) but it is ignored by the authors. Please correct accordingly.

There was an error when typing this data, which was corrected and the rest were checked to confirm the typing..

Standard deviations: Since it is not clear what was considered as the experimental unit (see comment for ln. 183-186), it is also not clear what variability these reported standard deviations represent.

All fish were sampled for analysis of zootechnical performance parameters. For hematological and biochemical analyzes and vicerosomatic, hepatosomatic and visceral fat indexes, 5 animals/tank (n=15) were used.

Table 2 and 3: FCR reported are too good ! Please recheck data and calculations and adjust relative discussion parts.

The data is correct. These FCR values are possible due to the collection of leftover feed after observing the apparent satiety of the fish in the tanks. These data are consistent with other studies on the species (10.1016/j.aquaculture.2020.736079; 10.1007/s10499-021-00647-z; 10.1016/j.aquaculture.2020.736274; 10.1016/j.aquaculture.2020.735689; 10. 1111/are.15196) and the hybrid tambatinga (C. macropomum x P. brachypomus) 10.33448/rsd-v9i5.3317.

Tables 2, 3, 6: The report of absolute food consumption (i.e. Kg) is not informative and is not correct for differently sized fish. Please express and report feed consumption as % of body weight and then repeat statistics. It is the only way to compare experimental treatments on a common basis.

Dear reviewer, we understand your doubt. However, consumption data was collected per tank, due to the number of animals kept in each experimental unit there was no way to collect individual consumption data. Another factor that does not allow us to calculate the % p.v. is the difference between the initial weight and the final weight of the fish in the three experiments. This difference makes it difficult to perform the calculations, increasing the possibility of error in the experiment. These factors do not allow for reliable results if percentage calculations are made, as they are an estimate.

Table 6: Standard deviations for parameters in D2 are very high. Why?

It is common to observe heterogeneity in batches of fish kept at low densities as described by Carvalho et al., (2018), which was reflected in the high standard deviation values. However, all data were subjected to normality analysis using the Shapiro-Wilk test and homogeneity using the Levene test to validate them. To make the parametric statistical analysis used in the study possible.

Table 6: Recheck FCR, since it is very strange that a value of 2.36 (D2) does not differ from a value of 1.36 (D6).

The data is correct. Heterogeneity between animals influenced the high standard deviation values of treatment D2, causing equality between treatments.

 

Discussion

Ln. 301-302: Italics for the scientific name.

Adjusted

Ln. 314: It would be useful to add fish/L for the present experimental treatments in Tables.

In the RAS System, it is not usual to use density in numbers of fish/L, but rather the biomass entered. However, the number of fish kept per tank was added to the description of treatments in the material and methods.

Ln. 319-327 (and major conclusion): Although I understand the authors’ point of view, productivity in aquaculture is not only “produced biomass”. Instead, final weight together with feed efficiency (FCR) and food consumption (as % body weight) are among the most important indices. Present results showed that increasing density resulted in lower final weight (Experiments 2 and 3) with better feed efficiency (not significantly different but lower values in Experiments 2 and 3). This is quite contradictory! Obviously, some involvement of feed consumption is indicated. However, unless feed consumption is expressed as % of body weight, the evaluation of productivity is incomplete. I strongly suggest the re-evaluation of results (and relative discussion) after the correct expression of feed consumption.

The choice of which stocking density to use must follow the production objective, producers who choose to work only with the tambaqui breeding phase, prefer to use higher stocking densities, allowing the production of greater biomass and number of animals, since will be sold individually.