Iron and Potassium Fertilization Improve Rocket Growth without Affecting Tilapia Growth and Histomorphology Characteristics in Aquaponics

Round 1

Reviewer 1 Report

Can be accepted 

Author Response

We thank the reviewer for his acceptance.

Reviewer 2 Report

This is an interesting paper about aquaponics focusing on the effect of adding K and Fe in an aquaponics system. Please find below some suggestions for improvements.

The introduction could include information about decoupled aquaponics.

Lines 35-36: RAS would also use less than 10% of conventional aquaculture systems so this is not specific to aquaponics.

Line 40: Please explain why the initial biomass if of importance: "as well as initial biomass".

Line 44: Please explain why a multispecies cultivation should be more efficient: "Sometimes a multispecies cultivation is more efficient in an aquaponic system".

Line 45: change "that" to "where".

Lines 48-50: Not connected to the brackish water aquaponics described above.

Line 82: Consider rewording: "The biological filter setup lasted" - change the word "lasted"?

Line 92: The breeding density is VERY low. Would higher breeding densities affect the results?

Line 139: The experimental time 30 days is very low. Would longer experiments affect the results?

Line 307: "Or lower"? Should this be "or higher"?

The results, discussions and conclusion could be more specific towards the research and its limitations should be taken into account.

 

 

 

Author Response

1. The introduction could include information about decoupled aquaponics.

The following part was added at the introduction. “Traditional aquaponics systems send nutrient-rich water from fish tank to the plants and back (single loop). Decoupled aquaponics systems separate the aquaculture and aquaponics units. In these systems, the sludge from the fish tank is digested in the bio-logical waste system which provides the nutrients for the hydroponic system. The wa-ter sent from the RAS to the hydroponic unit is consequently replaced by clean water which reduces nutrient concentrations and thus improves water quality [15]”. Lines 51-57.

2. Lines 35-36: RAS would also use less than 10% of conventional aquaculture systems so this is not specific to aquaponics.

For clarification we changed the sentence as “Aquaponics is a sustainable solution with a small environmental footprint [4], as it uses less than 10% of the water used in conventional agriculture [2]”. Lines 35-36.

3. Line 40: Please explain why the initial biomass if of importance: "as well as initial biomass".

The phrase “as well as initial biomass” was added by mistake to the sentence. Fish biomass and number of plants are important in an aquaponics system. So, the sentence was rewritten as “The type of the system, the filter size, fish species, fish biomass, number of plants and plant species must be carefully chosen, in order to have a successful production [8]”. Lines 39-41.

4. Line 44: Please explain why a multispecies cultivation should be more efficient: "Sometimes a multispecies cultivation is more efficient in an aquaponic system".

For clarification the following sentence was added “Different fish species used in identical aquaponic systems change oxygen levels and along with the combined feed input, alter plant species growth [16]”. Lines 49-51

5. Line 45: change "that" to "where".

We have made this change according to the reviewer comment.

6. Lines 48-50: Not connected to the brackish water aquaponics described above.

We removed the sentence “Until now, more than 150 species of vegetables, herbs, flowers, and small trees have been successfully used in aquaponics systems, with lettuce, tomato, basil, eggplant, pepper or spinach to be the most widely used [20-22]” at the start of the next paragraph. Lines 61-63

7. Line 82: Consider rewording: "The biological filter setup lasted" - change the word "lasted"?

We have changed these lines as “A two months period required for the setup of the biological filter setup. According to Hirayama [24], 40-60 days are necessary for the establishment of bacteria and the efficient oxidation of ammonia to nitrate ions”. Lines 94-96.

8. Line 92: The breeding density is VERY low. Would higher breeding densities affect the results?

We thank the reviewer for his valuable comment. We have no doubt that a higher breeding density would be beneficial as more nutrients would be produced. However, according to the ethics committee approval and the EU Directive 2010/63/EU guideline, special care had to be given in fish welfare. So, we chosen the lower breeding density that we believed that it would produce the required nutrients for the rocket growth.

9. Line 139: The experimental time 30 days is very low. Would longer experiments affect the results?

Rocket had a very rapid growth performance at the aquaponics system. At the thirty day the plants had cover the whole hydroponic tank and their leaves were overlapped. So, thirty days of experiment was the longest period that the system can afford.

10. Line 307: "Or lower"? Should this be "or higher"?

According to the reviewer comment we have rewritten the sentence as “Plant roots and nitrifying bacteria require at least 3 mg/L DO [34]”. Lines 313-314.

11. The results, discussions and conclusion could be more specific towards the research and its limitations should be taken into account.

We thank the reviewer for his comment. Please take in account that our system was not commercial, but a lab system with limitations to its dimensions. So, we couldn’t use commercial fish breeding density (we had also limitations for the ethics committee) and many rocket plants in the hydroponic tanks.

Some changes have been made at the discussion and conclusions part in order to clarify the K effect at the rocket growth. The following sentence was added to the discussion “K addition seems to be not indispensable for rocket growth. Considering the fact that K seems to accumulate to the gills and maybe this accumulation can have long-term effect to fish health, we would suggest that in aquaponics systems with rocket cultivation, no extra K addition is needed”. Lines 435-438.

Also the last part of the conclusions was rewritten as “All the above-mentioned results indicate that Fe fertilization can improve the production of rocket, while K addition seems to be not indispensable for rocket growth. Both K and Fe do not impact tilapia growth and health parameters examined here, and thus would not endanger food safety of aquaponics products”. Lines 460-462.

 

Reviewer 3 Report

The article deal with a trial where aquaponic system was tested for the farming of Red tilapia and the cultivation of rocket with the addition of Fe and K to promote the growth of the vegetable part of the system.

The topic is of interest as the combination solution provided by aquaponics must be developed to increase the sustainanility of modern fish farming and agriculture. 

There asr some issue that must be solved before the article could be considered suitable for the pubblication on Applied Sciences

The fish density was very far from a commercial aquaculture system and the farming procedure are not the one used in a real commercial RAS system. For instance the siphoning is not applicable in a commercial facility. By this procedure you have subtracted some of the nutrients released by the fish and therefore you have not made them available to the plants. Please provide some consideration about this aspect. 

Table 1 and following. Do not use letters to indicate value where there is no statisitcal difference. 

Line 282-287 please move this paragraph to the introduction.

Results suggest that K addition is not indispensable and so not reccommended for the growth of rocket in an aquaponic system, and associated with the accumulation of K in the gills of tilapias, which had no effect in the short term of your trial but which could lead to disturbances in the long run, suggests that there is no need to supply K to the system. Please provide some consideration about this aspect. 

Author Response

1. The fish density was very far from a commercial aquaculture system and the farming procedure are not the one used in a real commercial RAS system. For instance the siphoning is not applicable in a commercial facility. By this procedure you have subtracted some of the nutrients released by the fish and therefore you have not made them available to the plants. Please provide some consideration about this aspect.

We thank the reviewer for his valuable comment. We have no doubt that a higher breeding density would be beneficial as more nutrients would be produced. Please take in account that our system was not commercial, but a lab system with limitations to its dimensions.  Also, according to the ethics committee approval and the EU Directive 2010/63/EU guideline, special care had to be given in fish welfare. So, we chosen the lower breeding density that we believed that it would produce the required nutrients for the rocket growth.

Daily siphoning to the fish tanks was necessary in order to calculate food consumption.

2. Table 1 and following. Do not use letters to indicate value where there is no statisitcal difference.

We have changed the tables according to the reviewer comment.

3. Line 282-287 please move this paragraph to the introduction.

We have removed this paragraph to the introduction. Lines 43-48.

4. Results suggest that K addition is not indispensable and so not reccommended for the growth of rocket in an aquaponic system, and associated with the accumulation of K in the gills of tilapias, which had no effect in the short term of your trial but which could lead to disturbances in the long run, suggests that there is no need to supply K to the system. Please provide some consideration about this aspect.

We thank the reviewer for his valuable comment. The following sentence was added to the discussion “K addition seems to be not indispensable for rocket growth. Considering the fact that K seems to accumulate to the gills and maybe this accumulation can have long-term ef-fect to fish health, we would suggest that in aquaponics systems with rocket cultivation, no extra K addition is needed”. Lines 435-438.

Also the last part of the conclusions was rewritten as “All the above-mentioned results indicate that Fe fertilization can improve the production of rocket, while K addition seems to be not indispensable for rocket growth. Both K and Fe do not impact tilapia growth and health parameters examined here, and thus would not endanger food safety of aquaponics products”. Lines 460-462.