Apparent digestibility of proximate composition, essential amino acids and energy in full-fat and defatted black soldier fly larvae meal for Asian seabass (Lates calcarifer) fingerlings

Nguyen Duy Quynh Tram, Le Duc Ngoan¹ and Pham Thi Phuong Lan

Faculty of Fisheries, Hue University of Agriculture and Forestry, Hue University, Vietnam
ptplan@hueuni.edu.vn
¹ Faculty of Animal Sciences, Hue University of Agriculture and Forestry, Hue University, Vietnam

Abstract

This study aimed to determine apparent digestibility of proximate composition, essential amino acids and energy in full-fat and defatted black soldier fly larvae (BSFL) meals for Asianseabass fingerlings in brackish water with 10‰ salinity. Asian seabass fingerlings with an average initial weight of 14.5 g were randomly distributed into 12 tanks (25 fish per tank 160 L), fed one of 3 diets and 4 replicates/diet, namely FMD – a reference diet consisted of fish meal as main protein source and FFD and DFD were test diets formulated by 70% FMD and 30% full-fat or defatted BSFL meal, respectively. Titanium dioxide was added at 0.7-1.0% as marker and nutrient digestibility of full-fat and defatted BSFL meal was then calculated by the difference. The results showed that apparent digestibility of proximate composition and essential amino acids in full-fat BSFL meal were higher than in defatted BSFL meal (p<0.05), but digestible nutrients content including proximate and essential amino acids in two types of meals were comparable, except for ether extract and energy.

Keywords: brackish water, digestible amino acid, digestible energy, seabass juvenile

Introduction

In aquaculture, fish meal (FM) is considered as the main source of protein. However, the availability of wild-caught fish is declining and the use of FM protein has been warned to be unsustainable (FAO 2017). Rising prices and limited global supply of FM have resulted in high feed costs accounting for up to 60-70% of total production costs (Wilson 2002). Currently, many studies are focusing on finding protein-rich feed sources to replace FM in order to reduce feed costs and increase sustainability for aquaculture production (Rana et al 2015; Cammack and Tomberlin 2017).

One of the potential insect species used to replace FM in animal feed is the larvae of the black soldier fly Hermetia illucens (BSFL) (Dumas et al 2018; Ngoan et al 2021). Black soldier fly larvae are rich sources of protein and some essential amino acids such as lysine and methionine, good fat such as linoleic acid and alpha-linolenic acid and also provide adequate levels of essential minerals and vitamins at a level equivalent or superior to other insects, suitable for aquatic animal feed (Cammack and Tomberlin 2017; Lan et al 2022^a,b; Zabulione et al 2023; Suong et al 2023; Manh et al 2023; Nghia et al 2023). Besides, BSFL is an insect with a short longevity and raise easily, they can eat all kinds of organic waste such as animal manure, kitchen waste and contribute to the reuse of organic waste (Zheng et al 2012; Webster et al 2016). BSFL can digest large quantities of raw waste more quickly and efficiently than any other known species of fly due to their very powerful mouthparts and digestive enzymes (Tomberlin et al 2002; Kim et al 2011). Therefore, BSFL is considered as a good and sustainable feed ingredient in aquaculture.

In Vietnam, previous studies on using different substrates such as cassava by-products, brewers grains, tofu by-products and/or their mixtures for BSFL farming, it is found that, feeding BSFL by tofu by-products gave more advantages than others in term of larvae yield and crude protein content and lower crude fat (Thao et al 2021; Lan et al 2022^a; Quan et al 2023). In addition, tofu by-products are local available feed source and presently lower price as compared with cassava by-products and brewers grains in the research area. Therefore, in recently study, BSFL were fed by tofu by-products. In fact, BSFL could be used as fresh form and meal for aquaculture. However, high fat concentration in BSFL made it difficult to balance diets according to energy and fatty acids (Schiavone et al 2017^a,b). Normally, when the fat content in feed increases, the digestibility of the proteins present in the complex systems (such as emulsions) could be significantly decreased. Such phenomenon occurs because the products of the fat oxidation induce the aggregation of the larvae proteins, resulting in the limited access of the protease enzymes to the protein complexes (Obando et al 2015; Traksele et al 2021). In addition, the use of defatted BSFL meal reduces the concentration of harmful saturated fatty acids (SFA) and helps to balance the beneficial fatty acids in the larvae-based diet (Makkar et al 2014; Spranghers et al 2017). The defatting technology requires large financial resources such as machinery, factories and chemical solvents, which are difficult to apply to farm households (Kim et al 2016). However, the technology required for partial defatting can be as simple as a mechanical pressing of the larvae widely applied because of its low cost (Aniebo et al 2009; Russin et al 2011). Therefore, many authors recommended that fat reduction should only be applied to BSFL with over 25% crude fat content.

In previous paper, Lan et al (2023) reported that apparent digestibility of proximate composition and essential amino acids of diets contained full-fat BSFL meal were higher than that of FM-diet and defatted BSFL diet for Asian seabass juveniles in fresh water. Also, results showed that nutrient digestibility of full-fat BSFL meal was higher than defatted BSFL meal. Therefore, this study aimed to determine the apparent digestibility of proximate composition and essential amino acids of full-fat and defatted BSFL meal for Asian seabass juveniles rearing in brackish water.

Materials and methods

The experiment was conducted at the laboratory of the Faculty of Fisheries, University of Agriculture and Forestry, Hue University and was approved by the Advisory Council on Animal Ethics in Research of Hue University, Vietnam (code No: HU VN0017 dated April 10^th, 2022).

Larval meal and diet preparation

Larval meal preparation: BSFL were fed by tofu by-products and collected at day 7th after rearing at temperature 26-33°C. Larval meal preparation was followed Kroeckel et al (2012). Larvae were washed with water several times to remove all impurities and were divided into two parts: one for full-fat meal and another for defatted meal. In the first part, BSFL were boiled briefly in 100°C water to kill the larvae, then dried in oven at 60°C for 48h and milled into full-fat BSFL meal. The second part, BSFL were ground using a food processor. The ground larvae solid was put in a nylon bag and then carefully soaked in 60°C water for 5 minutes to take out some part of fat. The larvae solid was mechanically pressed to remove remained fat out of solid. Then, the remaining residue was dried at 60°C for 24h to grind into defatted BSFL meal. Chemical composition and energy of feed ingredients were presented in Table 1.

Diet preparation: All ingredients were carefully mixed according to their ratio in the diet. Then the mixtures were extruded through a 3 mm diameter die plate using an extruder (Sheng Kiang, China). Feed was chopped into pellets approximately 3 mm long, dried at 45°C for 24h and stored in plastic bags at room temperature prior to use. The proportions of ingredients and the nutritive value of the diets are presented in Table 2.

Experimental design

Asian seabass with an average initial weight of 14.5 g were purchased from Quoc Thang Company, Thua Thien Hue province, Viet Nam. Fish were randomly allocated in 12 tanks (25 fish per tank 160 L) and fed one of 3 diets and 4 replicates per diet. Dietary treatments named FMD as a reference based-fishmeal diet as main protein; FFD and DFD were the test diets that formulated by 70% FMD and 30% full-fat BSFL meal and defatted BSFL meal, respectively.

Feeding and management

The fish were acclimatized to the experimental conditions for a week and were fed with the test diets before the start to collect faeces. The fish was fed two times a day (8h and 17h) until apparent satiation. The uneaten feed was removed after feeding each meal every day. All water quality factors were measured periodically every day and measured twice per day (7h and 14h). Water temperature (°C) was measured by thermometer, pH by HI98107/Hanna handheld meter; NH₃ by HI 700/Hanna; dissolved oxygen (DO) by DO test kit of Sera (Germany); and salinity was measured by refractometer (Atago Model 2491-master's, Japan). Water quality parameters were recorded during the experimental period as follows: water temperature 25-27°C, pH 7.58-7.9, DO 4.08-4.5 mg/L and NH₃< 0.1 mg/L.

Chemical analysis

The diets, ingredients and faeces were analyzed for proximate composition: dry matter (DM), ether extract (EE), crude protein (CP), crude fiber (CF) and total ash (Ash) according to the Association of Official Analytical Chemist methods (AOAC 1990) procedures at the Lab of the Faculty of Animal Husbandry and Veterinary Medicine, HUAF. Amino acid compositions were analyzed by Performic Acid Oxidation with Acid Hydrolysis–Sodium Metabisulfite Method (AOAC 994.12; 1997); Titanium dioxide (TiO₂) was analyzed followed ICP (155 QĐ/VCN) at the Lab of Biotechnology of the National Institute of Animal Sciences, Ha Noi. Meanwhile, gross energy (GE) was calculated according to Ewan (1989):

GE (MJ/kg) = 4.184 x [4143 + (56 x EE + 15 x CP – 44 x Ash)]/1000

Apparent digestibility calculation

Faeces collection was carried out throughout 15 consecutive days of the digestibility trial. The fresh faeces were carefully siphoned from the tanks 3 hours after feeding, dried on filter paper and immediately kept frozen until being used for analysis.

The apparent digestibility (AD) for dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), gross energy (GE) and amino aicds of the diets were calculated using the following equations (Cho et al 1982):

AD of nutrient = 100 - [100 x (% faeces nutrient /% dietary nutrient) x (% dietary titanium dioxide /% faeces titanium dioxide)]

The AD of the test ingredients was calculated by the difference method basing the digestibility of the reference diet (FMD) and test diets (FFD and DFD) using the equation (Bureau and Hua 2006):

AD_I= AD _TD + (AD _TD - AD_RD) x (0.7 x D _RD / 0.3 x D_I)

Where: AD _I = AD of the test ingredients; AD _TD = AD of the test diet; AD _RD = AD of the reference diet; D _RD = % nutrient of the reference diet; D _I = % nutrient of the test ingredients.

Data analysis

Data were presented in the form of the mean (M), standard error of the mean (SEM). The data were statistically processed by analysis of variance (ANOVA) by General Linear Model in Minitab v. 16.2 (2010). The difference between the mean values was determined by the Tukey method at a confidence level of 95%. Statistical model:

Y_ij= µ + T_i+ e_ij

Where: µ is the average value; T _i is the effect of diets or feed ingredient; e_ij is the experimental error.

Results and discussion

The apparent digestibility of nutrients in diets

Data in Table 3 showed that apparent digestibility (AD) of proximate composition, essential amino acids and gross energy of diets was differed among treatments. The AD of DM, OM, CP and energy in FFD were higher in FMD and DFD (p<0.05). Similarly, AD of essential amino acids was also higher in FFD than in FMD and DFD (p<0.05). These findings are in agreement with previous results of Lan et al (2023), who reported that apparent digestibility of nutrients of full-fat BSFL diet was higher than in fishmeal diet and defatted BSFL meal for seabass fingerlings kept in fresh water.

The apparent digestibility of nutrients in full-fat and defatted larval meals

The AD of nutrients and energy in Table 4 was differed between full-fat and defatted BSFL meals (p<0.05), except the AD of histidine had no statistical difference (p>0.05). The AD values of DM, OM, CP, EE and GE were higher in full-fat BSFL meal than in defatted BSFL meal. Similarly, the AD of all essential amino acids was higher in full-fat than in defatted BSFL meal (p<0.05).

Data in Table 1 show that, the CP of larvae meal was higher than fishmeal and of defatted was higher than full-fat BSFL meal (65% compared to 58.7%), the CF was 2 times higher (21.1% compared to 10.8%), but the gross energy was lower (22.2 MJ/kg versus 23.7 MJ/kg). This means that defatting method affected the nutritive value and energy of BSFL. In this study, the method of dipping ground larvae solid in boiling water before mechanical pressing had some limitations such as reducing soluble protein and mineral contents in the larvae. Therefore, we recommend that, appropriate method of larvae defatted process can be further studied.

According to Peres and Oliva-Teles (2006), protein requirement in the diet for seabass about 40-50% and the optimal for level growth is 40-45%. According to NRC (1993), the AD of protein-rich ingredients typically ranged from 75% to 95% in fish, that was agreement with this study. In this study, the AD of CP ranged from 87.6-93.6%, that are in agreement with NRC recommendation. Meanwhile, Glencross (2008) reported that the AD of CP of poultry meal 54-79% and soybean meal 85% in fish. As compared with the AD of CP in seabass in this study was higher than previous publications in other fish. In rainbow trout (Oncorhynchus mykiss), the AD of CP for defatted BSFL meal 85% (Dumas et al 2018); 63.1% in Psetta maxima fingerling (Kroeckel et al 2012); 86.5% in Acipenser baerii (Christian et al 2020). Meanwhile, Magalhães et al (2017) reported that the AD of DM, CP and EE in European seabass fed full-fat BSFL meal were 69.8%; 91.6%; and 81.5, respectively. In hybrid grouper fed larval meal, the AD of DM, CP and EE ranged 61.4-80.5%; 81.1-88.3%; and 95.2-99.3%, respectively (Mohamad-Zulkifli et al 2019).

In addition, the CF and EE concentrations in feed affected the digestibility of aquatic animals. Specifically, high CF concentration increases the speed at which feed passes through the digestive tract, leading to increase feed intake but reduce growth performance (Hien and Tuan 2009). The increase in EE content in feed can significantly reduce the digestibility of CP (Obando et al 2015; Traksele et al 2021). Thus, seabass fingerlings have a higher digestibility for full-fat BSFL meal than defatted meal, which was completely suitable in this study.

Digestible nutrients in full-fat and defatted BSFL meals

Calculated digestible nutrients including proximate composition and essential amino acids in full-fat and defatted BSFL meals presented in Table 5. Even though, higher digestibility of nutrients in full-fat BSFL meal, but digestible nutrients in full-fat BSFL meal were comparable, except for EE and digestible energy (DE) concentrations were higher in full-fat BSFL meal. In general, 1 kg DM BSFL meal contained 548.9-569.6 g digestible protein and 14.3-19.4 MJ DE and 28.3-36 g digestible lysine and 15-18.2 g digestible methionine.

Conclusion

In Asian seabass fingerlings stocking in brackish water with 10‰ salinity, apparent digestibilities of proximate composition and essential amino acids in full-fat black soldier fly larvae meal were higher than in defatted black soldier fly larvae meal, but digestible nutrients including proximate and essential amino acids in two types of meals were comparable, except for ether extract and energy.

Acknowledgement

The authors acknowledge the financial support by Hue University under the Core Research Program (Code: 06/HĐ-ĐHH).

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