Effect of replacing dietary soybean meal with black soldier fly (Hermetia illucens) larvae meal on performance of nile tilapia (Oreochomis niloticus)

A Musoni, C Uwizeyimana, G Dusabemungu, R Gatare, P Nambajimana, A Kanimba, A Kayitesi and P Nyabinwa

Department of Animal Resources Innovation and Technology Transfer/ Rwanda Agriculture and Animal Resources Development Board (RAB), Rwanda (5016)
nyabipassi@gmail.com

Abstract

A 84-day feeding trial was conducted at Kigembe Aquaculture farm to assess the effects of substitution of dietary soybean meal with black soldier fly (Hermetia illucens) larvae meal (BSFLM) on the growth performance, survival rate, and feed conversion ratio of Nile Tilapia (Oreochomis niloticus). Five test diets were formulated and substitution of soybean meal by BSFLM made at 0%, 25%, 50%, 75%, and 100%. 400 male Nile tilapia (9.9±0.4 g) were divided into 2 groups (2 replicates) each and were placed in 10 hapa nets (40 fish/hapa). The all five treatments of fish were fed diet two times a day. The fish were fed at 8% body weight at the beginning (first month), 6% for the second month, and then 5% of body weight/day was used for the last month of culture period. Physico-chemical parameters were monitored weekly while sampling of the fish was done biweekly. The weight gain, and specific growth rate of the Nile tilapia were significantly different (p<0.05) among treatment diets. In contrast, the survival rate and feed conversion ratio were not significantly different (p>0.05) among treatment diets. The present study indicates that the optimal results were achieved where soybean meal was replaced by 50%BSFLM. This is indicative that BSFLM can be considered as one of the best alternatives for partial or complete replacement of soybean meal in Nile tilapia diets that warrants the adoption of this animal protein source to fish farmers to sustainably produce cheap and nutritious fish feed capable of increasing yields and maximizing profits. Further studies should determine the profitability potential of using black soldier fly larvae to manage various organic substrate streams.

Keywords: animal protein, feeding trial, fish feed, Kigembe, Rwanda

Introduction

Nile tilapia (Oreochromis niloticus) is the mainstay of Rwandan aquaculture production primarily conducted in ponds and cages farming. Plan for Agriculture Transformation, 2018-2024 (PSTA4) under the general framework of National Strategy for Transformation recognizes that the farming of fish and other aquatic species have the great potential to make an important contribution to the agriculture sector. In Rwanda, aquaculture production was estimated at 4,900 tons in 2022 (MINAGRI 2022) and the Government needs to promote aquaculture as an important means to increase per capita consumption of fish and contribute to its vision 2050. The current status of Rwanda’s fish production is 4,028 tons of Nile tilapia (Oreochromis niloticus), 572 tons of African catfish (Clarias gariepinus) and 276 tons of other species such as common carp, totaling 4,876 tonnes in 2021 (Of 2022). This indicates that Tilapia is currently the most farmed fish in Rwanda.

One of the problems in tilapia culture in Rwanda is higher in production cost, especially for the feed. This is because the Nile tilapia feed has higher protein content (30-56% crude protein) which contributes mostly from both the soybean and fishmeal This indicates that protein source is more costly in fish feed formulation (Abdel-Tawwab et al 2010). However, there is a greater market competition between different animals that need soybean meal in their feed formation including human beings who need this protein source in the diet. This is an indication that soybean meal is becoming a less reliable protein source. Fish feed makes up roughly 60% of the production costs of a fish farm (Elangovan et al 2017). The present cost of feed in Rwanda is significantly higher (at c.a. USD 1,150 per tonne) than for other regional countries (c.a. USD 900 per tonne) due to the low level of supply and transportation costs (MINAGRI 2022). Therefore, it was very urgent to explore alternative protein sources from animals to replace that one from plant which reduces pressure on available land and is cheaper than that soybean meal The BSF (Hermitia illucens) is a harmless insect with a potential to solve two of modern agriculture’s growing problems, namely, serve as an alternative protein source for animal feeds and disposal of organic wastes, byproducts and side streams. Ahmed Tumpa et al (2021) stated that BSF has an ability to transform low quality organic wastes into high quality protein that can be utilized in the production of feeds for Nile tilapia, allowing for the aquaculture production to remain economically and environmentally viable. Also, insects are consumed naturally by fish and other animals. Therefore, we can assume that these animals are evolutionarily adapted to eating them as a part of their regular diet. Furthermore, BSF larvae meal, produced from the larvae of Hermetia illucens, has shown promise as a fish meal replacement in diets for catfish and tilapia (Ahmed Tumpa et al 2021). BSF has over 42% high quality protein and 35% fat making it suitable for use as an alternative protein source in animal feeds(Hender et al 2021). Therefore, the present study was conducted to produce BSF and to evaluate the efficiency of protein from Black Soldier Fry meal replacing Soybean (SB) meal protein in Nile Tilapia diets.

Materials and methods

Black soldier flies’ larval production

The BSF production was carried out over a period of 90 days (from December 2021 to February 2022) in a small house prepared for rearing the BSF located at Kigembe aquaculture farm, Gisagara district, Southern province of Rwanda. The prepupae used for this research were supplied by Maggot Farm Production Ltd located in Kayonza District, Eastern province (https://bsfrwanda.com/). They were supplied 30 kg of prepupae for adaptation and multiplication. After two weeks those prepupae were metamorphosed into flies which laid eggs for incubation in plastic basins. Eggs were collected before hatching, so harvests were scheduled three times a week using manual technique. They were fed on fruits mixed with vegetables (banana peels, oranges, pineapples, avocados, and watermelons) and brewers’ waste. Therefore, a uniform feeding rate between 100-150mg/larva/day substrates were weighed and distributed to the feeding containers (Diener et al 2011). In the current experiment, water was supplied daily (about 2 L/day) using a pressurized water gun that allows spraying small droplets on the coved net housing the flies.The feeding was controlled until they reached the prepupae stage. Subsequently, all the prepupae and any remaining larvae were separately harvested by sieving through a 5mm diameter mesh screen and supplemented by manual picking of small sized larvae that may have passed through the sieve together with the residue(Ajani et al 2004).

Experimental design and feed formulation

The feeding of BSFLM to Nile Tilapia Fish (Oreochomis niloticus) was carried out over a period of 84 days (from March 2022 to May 2022) at Kigembe aquaculture farm, Gisagara district, Southern province of Rwanda. The BSF larvae (prepupae) were prepared based on the method of Ajani et al 2004, they were killed in an oven at 60ºC for 24 hours and sun dried until constant weight. The dried BSF larvae were then pounded in mortar to produce a meal that was then analyzed for quality control purposes. The other ingredients used together with BSFL meal (BSFLM) were also analyzed before their mixing (Table 1). Five isonitrogenous (35% crude protein) were formulated to replace Soybean meal using BSFLM at 0% (control diet, diet without black soldier fly larvae meal inclusion), 25% (BSFLM₂₅), 50% (BSFLM₅₀), 75% (BSFLM₇₅) and 100% (BSFLM₁₀₀, 100%). BSFLM, dried fish meal and soybean meal served as the major protein sources in the experimental diets while rice bran, wheat, and cassava flour were the carbohydrate sources (Table 1). Soybean meal was substituted at graded level and accordingly adjustments were done in other ingredients to balance the protein and lipid content in all experimental diets. Feeds were designed and formulated to meet the optimum nutrient requirement of experimental fish, following the nutrient requirements and recommended for tilapia fingerlings (M. El-Sayed 2006). After thoroughly mixing the dry ingredients the filtered tap water was added to attain a consistency for pelleting and make a soft dough of the powdered mixture. The experimental diets were, therefore, pelleted with a simple pelleting machine without heating, using a 2-mm diameter and drying in air-lightroom. The pellets were sun-dried and stored at room temperature.

Proximate composition of the individual ingredients and test diets was analyzed dry matter, crude protein, crude fat, and ash content using the standard proximate analysis method (General et al 2023) (Table 2).

Experimental fish and feeding trial

Tilapia fingerlings (Oreochromis niloticus) averaging 9.9±0.4 g of mean weight was acquired from the nursery pond of Kibembe and randomly distributed in ten hapa assigned to five treatments each in duplicate groups where fish were stocked in hapas settled up in an outdoor pond. The total fish counted and stocked in each hapa was 40 fish (a stocking density of 4 fish/m²). The all five treatments of fish were fed diet twice daily (10:00 am and 15:00 pm). Tilapia fingerling was fed at 8% body weight at the beginning (first month), 6% for the second month, and then 5% of body weight/day was used for the last month of culture period. The total fish weight in each hapa was determined in every 2 weeks interval to avoid the stress of fish, and the amount of feed fed to the fish was adjusted accordingly.

The present study followed the ARRIVE guidelines and was carried out in accordance with the U.K. Animals (Scientific Procedures) Act, 1986 and associated guidelines, EU Directive 2010/63/EU for animal experiments, or the National Research Council's Guide for the Care and Use of Laboratory Animals.

Analysis of the experimental data

At the end of the study, all fish from each treatment were weighed as) to determine the following measures indicated in Table 3.

Statistical analysis

Continuous variables were tested for normality using a Shapiro-Wilk normality test . Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) Statistics version 20.0 for Windows package software. The analysis of growth data was performed using polynomial regression models that fit asymptotic curves to the data. The model correlation coefficient (R²) was calculated as a measure of fit for each model; the R² represents the proportion of variance in the output variable that can be explained by the input variable.When a significant treatment effect was observed, a Duncan test was used to compare means. Treatment effects were considered at p<0.05 level of significance.

Results

The dissolved oxygen levels were averaging 5.5mg L^-1, water temperature 24.29^oC, pH was 6.71 and ammonia was less than 0.1mg/L (Table 4). These parameters were recorded two times (morning and afternoon) weekly but as all hapa were installed in one pond all parameters were the same in all hapa. It means that those parameters were measured because they can affect fish health not to test the significant in different hapas of treatment.

The growth performance, feed conversion ratio, and survival rate of Nile tilapia fingerlings fed on the experimental diet for 84 days are presented in Table 5. At the end of the study period, mean weight gain achieved by Nile Tilapia fingerlings varied from 36.6g (Control) to 39.8g (BSFLM75%). Mean weight gain recorded for the fish fed with diet containing 75%BSFLM and 50%BSFL were significantly higher (p<0.05) than that of the control diet while both diets contained 25%BSFLM and 100%BSFLM did not differ from that of the fish fed with the control diet (p>0.05). The specific growth rate (SGR) ranged from 1.7 (g% day^-1) to 1.8 (g% day^-1). The higher SGR was recorded in fish fed on the diet containing 50%BSFLM, but this value was not significantly different with the control diet and BSFLM 25%, 75%, and 100% (p>0.05).

Similarly, the lowest FCR was recorded at BSLM50%, but the values were not significantly different with control diet, BSFLM 25%, 75%, and 100% (p>0.05). However, the higher SR was found in fish fed with BSFLM 25%, but this value was not significantly different with other treatment diets (p>0.05, Table 5). Generally, the BSFLM gave a significant effect on the weight gain (WG), and specific growth rate (SGR) (p<0.05), but didn’t give a significant effect on the survival rate (SR) and feed conversion ratio (FCR) (p>0.05).

All the three polynomial function significantly explain the data (p< 0.05) (Table 6) and high R² for all. However, the cubic one explains better than others. This is because. The cubic function is the best for the data description as it has the lowest standard error estimate (1.35) compared to the other two.

Body weights (BW) of tilapia from nursey pond to 12 weeks are presented in Figure 1. The mean BW were significantly different (p<0.05) among tilapia that were fed different diets from week 0 to week 12.

The current experiment is a production function design in which variations in the input in this case the BSFL meal replacing soybean meal are reflected in the outputs which are the growth rate (Figure 1) and feed conversion of Tilapia (Figure 2).

Figure 1. Effect of replacing soybean meal by BSFL Meal on the growth rate of Nile Tilapia (Oreochomis niloticus)	Figure 2. Effect of replacing soybean meal by BSFL Meal on feed conversion ratio of Nile Tilapia (Oreochomis niloticus)

Discussion

The results of this study show that replacement of soybean meal with maggot meal at various percentages (25-100%BSFLM) of dietary treatments have a significant effect on growth, survival rate, and FCR. These results agree with those obtained by Ajani et al 2004 who concluded that 100% maggot meal in Nile tilapia diets is cost-effective and may reduce the cost of feeding by as much as 50% without affecting fish growth.

Fingerlings fed the control diet (0%BSFLM) presented the lowest growth performance than that fed diet containing 50%BSFLM and 75%BSFLM. This finding is in agreement with that proved by Nguyen et al 2009. He found that high inclusion of plant protein in fish diets have frequently been reported to result in reduced growth attributed to poor palatability, high crude fiber, reduced digestibility of lipid and energy, imbalance of essential amino acids and presence of anti - nutritional factors leading to a depression in daily weight gain. Insect meal (IM) is a good source of protein, minerals, and vitamins, similar to Fish Meal It is also rich in essential amino acids, especially lysine, methionine, and leucine, containing no anti-nutritional factors (Baiano 2020).

Tilapia fingerlings fed the control diet had statistically similar weight gain as those reared on the diet containing the highest level of BSFL meal even though the replacement of soybean meal by BSFL meal did not show a significant difference compared to the control diet, the results showed a decrease at 100% soybean meal replacement. This may be attributed to the chitin content in BSF larvae, the chitin content of BSF larvae has been reported to range from 6 to 9% and to reduce fish growth (Shumo et al 2019). Even if the protein value of insect meals is known to be superior to soybean meal it has chitin as major component of black soldier fly larvae that has been reported to negatively affect the digestibility of BSFL meal in fish that lack chitinase activity (Eggink et al 2022; Rathore & Gupta 2015). Nile tilapia, an omnivorous species with a great ability to feed on plankton, may possess some advantages in chitin degradation and digestion. The presence of chitin in insect meal might interfere with the utilization of protein (Eggink et al 2022). The similarities observed between the results from survival rate when the fish were fed BSFLM showed that the feed formulated with maggot meal is of interest for aquaculture.

The mean specific growth rate recorded for diets 3 (where soybean meal was replaced 50% by black soldier fly larvae meal) is optimal to all treatments. This result proved the well acceptance of replacement of soybean meal by black soldier fly larval meal for Nile tilapia. Considering the increased specific growth rate and weight gain as well as lower feed conversion ratio for diet 3 that contained 50%BSFLM meal could decrease the production cost. However, compared to the present study, the growth performance of Tilapia in the study of Dietz and Liebert (Dietz & Liebert 2018) were quite low with no difference significantly from the control diet, in which SGR ranged between 1.2 and 1.3 after 56days. In general, tilapia of all treatments in the present study showed high growth performance (between 1.8 and 1.9).

Feed conversion ratio (FCR) is an important economic indicator in the feed production industry. The FCR is also an indicator of how efficiently an animal utilizes feed, and therefore, minimizing feed wastage (Attalla and Mikhail 2008). Low FCR is usually desired in feed production. The FCR produced in this present study was quite good and ranged from 2.6 to 2.8 even though the optimal results were achieved for the fish fed diet containing 50%BSFL meal (FCR= 2.6). In addition, the visual observations of the feeding behavior, the fish showed that there were no palatability issues with the BSFLM-containing experimental diets. Similarly, Dietz and Liebert 2018 reported that the inclusion of 50% BSFLM as a replacer for soy protein-concentrate did not compromise the growth performance and FCR of Nile tilapia. Similar to our findings, these aforementioned studies also didn’t report the limitations in replacing soybean meal using insect meal.

Conclusion

• The optimal results were achieved where soybean meal was replaced by 50%BSFLM.
  
  
• BSFLM can be considered as one of the best alternatives for partial or complete replacement of soybean meal in Nile tilapia diets

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