Performance Evaluation of Available Strains of Nile Tilapia (Oreochromis niloticus) Fed Commercial and Locally-Made Feeds in the Democratic Republic of the Congo

Round 1

Reviewer 1 Report

The paper is well written and has relevant information. The authors need to clarify why the ponds were fertilized yet the fish were being fed commercial diets and formulated diets which provided all the nutrients 

The authors to indicate the size of the pond where the hapas were installed

Attached is the file with the comments 

Comments for author File: Comments.pdf

Author Response

Thank you very much for your comments.

 

Comment 1: What was the size of the pond ?

Response 1: Page 3 Line 110: The size of the ponds (33 m x 16 m each) is now included in the manuscript.

 

Comment 2: Application of fertilizer would mean natural productivity contributed to the nutrients available for the fish. Is this accounted for?

Response 2: Page 3 Line 127: The fertilization only occurred during the preparation of the pond. During the experiment, no additional fertilization occurred and the bulk of the food for experimental fish was provided though feeding of the experimental feeds.

 

Comment 3: separate the formula so that they are not joined this is confusing

Response 3: Page 6 Line 274-279: The formulas are now all separated to avoid confusion.

Reviewer 2 Report

I think I have a question about the use of the blood meal, this was not specified if this was pork or cow in origin. Moreover regarding the fishmeal substitute, was this considered a thrashfish in the area, one that the locals do not consume? If they do consume them, then there is a problem with human consumption and animal feeding. The authors did not explain whether the fishmeal substitute such as soybeans are locally cultivated in the area or grown. If this was imported, could it be sustained locally for the production of feeds? Regarding the number of times of feeding such as 4x a day, was this considered as ad libitum or until the fish were satiated? Or this is the common local practice in the area regarding feeding of Nile Tilapia in Hapa cages? In the sample collection and analyses, why were deep freezing of samples practiced? Why were water quality parameters collected and not analyzed or related to the growth of the fish? Since the cost of the fishmeal free diet was lower, do you think you can advise the fish farmers to actually adopt the feed technology despite it having a lower effect in terms of growth of the fish compared to the commercial diet? Is there a policy change that could be instituted by the government of Congo for this to happen? Or do you think there should be a follow-up study regarding the testing of the feeds? What could probably help increase the growth/weight of the Tilapia compared to the commercial feed? Please provide ingredients or annotation regarding the vitamin premix in Table 1 and make sure that the numbers there are in grams because I do not see any units. Regarding the Experiment 2, why conduct this experiment using commercial feed when in fact, fishmeal free diet is effective or as effective as the CF? What is the reasoning behind the use of CF instead of the fishmeal free diet?

Author Response

Thank you very much for your comments:

Comment 1: I think I have a question about the use of the blood meal, this was not specified if this was pork or cow in origin.

Response 1: Page 14 Table 1: information on the origin of the blood meal has been added as follows “Blood meal (cow)”

 

Comment 2: Moreover regarding the fishmeal substitute, was this considered a thrash fish in the area, one that the locals do not consume? If they do consume them, then there is a problem with human consumption and animal feeding.

Response 2: Page 4, Line 114: Yes, it was trash freshwater fish and it now read in the text “…a locally-made feed containing 30% local fishmeal (trash freshwater fish) in…”

 

Comment 3: The authors did not explain whether the fishmeal substitute such as soybeans are locally cultivated in the area or grown. If this was imported, could it be sustained locally for the production of feeds?

Response 3: Pages 9 and 14: Yes, the soybean was produced locally, and it now reads in the pages 9 Line 415 and page 14 (table 1) “the local full-fat soybean”

 

Comment 4: Regarding the number of times of feeding such as 4x a day, was this considered as ad libitum or until the fish were satiated? Or this is the common local practice in the area regarding feeding of Nile Tilapia in Hapa cages?

Response 4: For the purpose of this experiment, and considering that we wanted to collect information on the amount of feed delivered, ensure that the fish eat and use the experimental feeds properly and avoid feed wastage, we applied restricted feeding, as it was explained in the texte at Page 4, lines 172-176 as follows: “During the experiment, the fish were hand-fed four times daily (8h, 10h, 12h and 16h), seven days a week, at the feeding rate of 10% feed/unit wet body weight/day initially. The feeding rate was gradually reduced to about 8% after 21 days, 5% after 42 days and 4% after 70 days. Each feeding episode in all the hapas lasted a maximum of one hour and the fish were observed during the feeding to assess whether the feeding rate was adequate and changes were made accordingly to avoid feed wastage.”

 

Comment 5: In the sample collection and analyses, why were deep freezing of samples practiced?

Response 5: Page 4: The goal of the deep-freezing was to keep the samples in good condition until we conduct the analyses. For clarity purpose, we have edited the text as follows in Page 4, lines 182 and 191 : “… deep-frozen until further proximate analysis…”

 

Comment 6: Why were water quality parameters collected and not analyzed or related to the growth of the fish?

Response 6: In the experiment 1, all the treatments were applied in hapas mounted in the same pond. Therefore, the water quality parameters were the same for each experimental unit (happa) found in the same pond. Moreover, the statistical model corrected for the pond effect (block) as you can see in the table 2.

In the experiment 2, all the 9 experimental hapas were all mounted in the same pond. Therefore, the pond effect was minimized.

 

Comment 7: Since the cost of the fishmeal free diet was lower, do you think you can advise the fish farmers to actually adopt the feed technology despite it having a lower effect in terms of growth of the fish compared to the commercial diet?

Response 7: Yes, if the commercial feed is not readily available and affordable, the farmers or local feed miller can produce their own local fishmeal-free feeds.

 

Comment 8: Is there a policy change that could be instituted by the government of Congo for this to happen? Or do you think there should be a follow-up study regarding the testing of the feeds?

Response 8: Policy change is beyond the scope of our work, but once the paper will be published we will start dialogues with stakeholder to see if the paper can be used to influence aquaculture policies in Dr Congo, but that it all we can do.

 

Comment 9: What could probably help increase the growth/weight of the Tilapia compared to the commercial feed?

Response 9: As mentioned in the conclusion, information on the digestibility of the local ingredients will allow a better feed formulation, leading to cost-effective balanced diets that are comparable to any commercial diet.

 

Comment 10: Please provide ingredients or annotation regarding the vitamin premix in Table 1 and make sure that the numbers there are in grams because I do not see any units.

Response 10: The mineral and vitamin premixes were purchased in the local market and it is written in the text (Table 1 footnotes) as follows: “^a Mineral and vitamin premixes were purchased from a feed store in the market in Bukavu, and there were no indication on their composition.”

 

Comment 11: Regarding the Experiment 2, why conduct this experiment using commercial feed when in fact, fishmeal free diet is effective or as effective as the CF? What is the reasoning behind the use of CF instead of the fishmeal free diet?

Response 11: The experiment 2 was conducted in Kinshasa, with the goal to perform a strain comparison and not feed comparison. In Kinshasa, we did not have access to neither a pelletizer nor an extruder and could not prepare the experimental feed ourselves.

Reviewer 3 Report

Please refer PDF file

Comments for author File: Comments.pdf

Author Response

Comment 1: Page 1, Line 30: use p<0.05

Response 1: In the abstract, (P<0.05) has been added everywhere the was a significant result and (P>0.05) was added where there was not a significant result.

 

Comment 2: Page 2, Lines 45-46: Need to be corrected

Response 2: I have added a coma before in the sentence, to make it more comprehensible and it now reads “Despite the recent developments in aquaculture in Africa (Adeleke et al., 2020), the sector is yet to realize its full potential (Brummett, Lazard, & Moehl, 2008), as aquaculture only contributed 18% of the total fish production on the continent in 2018 (FAO, 2018, 2020).”.

 

Comment 3: Page 2, Lines 54-55: Is the statement is true? Is so give reference

Response 3: The statement is true, and most of the co-authors are based in the Democratic Republic of the Congo. However, we don’t have a reference to support that statement, therefore we will delate the sentence from the text, as the deletion does not change anything on the quality and articulation of the paragraph. Moreover, but deleting this sentence, the contradiction with the next reviewer’s comment is solved.

 

Comment 4: Page 2, Lines 59-61: Contradictory to line no 54

Response 4: The statement in the line 54-55 has been deleted and there is no contradiction in the paragraph anymore.

 

Comment 5: Page 3, Lines 108: Oversize the experimental design

&

Comment 6: Page 3, Lines 1010-111: Already mentioned in above para. May be deleted

 

Response 5 &6: The entire paragraph was rewritten, taking into account the reviewers' comments 5 and 6 and now reads “The experiment was conducted using a 2 × 3 factorial randomized complete block design. The experiment was carried out in net enclosures referred to as “hapas” (experimental units) of 1.1 × 0.9 × 0.8 m (0.8 m² surface) each, with 1 mm mesh size. The hapas were installed in ponds.  The first factor was ‘strain’, with two levels, the Nyakabera and Lake Kivu strains. The second factor was ‘feed’, with three levels, a commercial feed manufactured in Zambia, a locally-made feed containing 30% local fishmeal (trash freshwater fish) in the diet and a fishmeal-free locally-made feed. Ingredients available in the local markets of Bukavu, South Kivu, were used to formulate the last two feeds (WorldFish, 2018). There were thus six treatments (two strains × three feeds), with each treatment applied in triplicate.  There were therefore 18 experimental hapas (2 × 3 × 3), with nine hapas per strain (“Nyakabera” or “Lake Kivu” strains) and six hapas receiving each of the three experimental feeds. The experiment was conducted in three experimental ponds (blocks), with one replicate for each of the six treatments applied in one pond (block). ”

 

Comment 7: Page 3, Lines 122-131: This may be kept is separate section of pond preparation or pre-stocking management

Response 7: The text is now placed in a new section titled “2.1.2. Pond preparation”, as per the reviewer’s suggestion.

 

Comment 8: Page 3, Lines 133-146: Avoid repetition. This part need to be shotrten

Response 8: To avoid repetition, the first sentence (“The first syntheseTwo strains of Nile tilapia were used in the experiment, the Nyakabera strain and the Lake Kivu strain”) has been deleted. In addition, the text has been rewritten and re-organized to make it easy to understand and it now reads as fllows: “The Nyakabera strain was introduced to the Nyakabera station in Bukavu in 2005 from the Université Nationale du Rwanda, Rwasave fish farming station in Butare, Rwanda (F. J. Nihoreye, Masilya, Isumbisho, & Okitayela, 2019). This Nyakabera strain is described as a mix of Ivorian and Egyptian strains of Nile tilapia that was introduced to the l'Université Nationale du Rwanda de Rwasave in Butare from Auburn University in the US, between 1984 and 1985 (Fakage John Nihoreye et al., 2019). The broodstock used to produce the fry of the Lake Kivu strain used in the experiment were collected from the Bukavu basin of the Lake Kivu and bred at the Nyakabera government station. The two strains are referred to as the Nyakabera strain and the Lake Kivu strain in the various sections of the present paper only for simplicity and consistency with the appellations used by other authors who worked with these strains in the past (F. Nihoreye, Muzumani, & Nshombo, 2009; Fakage John Nihoreye et al., 2019; F. J. Nihoreye et al., 2019).

The eggs and larvae from the two strains were incubated and reared at The President Olusegun Obasanjo Research Campus, in Kalambo, South Kivu, before being transferred to the Nyakabera fish station, where the experiment was conducted. Each of the experimental hapas were stocked at a density of 30 fish/0.84 m² of hapa (300 fish per hapa) for a total of 5400 fry for the 18 hapas. The average initial weights ± standard deviation of the fish were 0.84 ± 0.06 g and 0.84 ± 0.02 g for the Nyakabera and Kivu strains, respectively.”

 

Comment 9: Page 4, Lines 152: Keep sub heading feed and formulation

Response 9: The sub-heading has been modified and improved, taking into account the reviewer’s comment and now reads “Feed formulation and feeding”.

 

Comment 10: Page 5, Lines 208: Hard to read the design. It has to be reduced

Response 10: The entire sub-section has been improved and is now better organized, and has short sentences.

Round 2

Reviewer 2 Report

I want the authors to discuss further in the introduction regarding difference between bloodmeal based feeds and fishmeal based feeds and their differences and where or which species of fish they are usually used and applied and during what stage of cultivation. In the discussion, there was no comparison made between the commercial feeds vs the bloodmeal based and fishmeal based feeds. I think the authors should elaborate more on that regarding growth, weight gain, protein efficiency ratio and lipids. I think the authors did not discuss that further. And whether this can also be applied with regard to other aquaculture species.

Author Response

Comment 1: I want the authors to discuss further in the introduction regarding difference between bloodmeal based feeds and fishmeal based feeds and their differences and where or which species of fish they are usually used and applied and during what stage of cultivation.

Response 1: Please, there is no blood meal-based feed in the experiment 1 in Bukavu. Both experimental diets had blood meal. The differentiator in the two diet was rather the fish meal, as fishmeal was present in one diet and absent in the other diet (while the blood meal was present in both diets, although in different proportions in order to balance the diets). That is why we talk in the article about the fishmeal-based and fishmeal-free feeds. It is already written that the blood meal was found locally, so elaborating on the blood meal in the introduction and the discussion may divert the paper from the main focus around local fish feeds that do and do not contain fishmeal.

 

Comment 2: In the discussion, there was no comparison made between the commercial feeds vs the bloodmeal based and fishmeal-based feeds.

 

Response 2: our response is the same as above; elaborating on the blood meal in the introduction and the discussion may divert the paper from the main focus around local fish feeds that do and do not contain fishmeal.

 

Comment 3: I think the authors should elaborate more on that regarding growth, weight gain, protein efficiency ratio and lipids. I think the authors did not discuss that further. And whether this can also be applied with regard to other aquaculture species.

 

Response 3: I the paper, we have elaborated on regarding growth, weight gain, protein efficiency ratio and lipids, as directed by the statistical results presented in the tables 2, 3, 5 and 6 and it is briefly appropriately discussed in the line 456. Moreover, we prefer to focus our results on tilapia and not extrapolate on other fish species, as fat metabolism is species-specific.

Reviewer 3 Report

Authors have taken hard effort to correct the manuscript. It may be considered with minor changes

Author Response

Comment 1: Authors have taken hard effort to correct the manuscript. It may be considered with minor changes.

Response 1: Thank you very much.