| Livestock Research for Rural Development 38 (3) 2026 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study aimed at evaluating the effect of the inclusion of fresh or dried black soldier fly larvae in diets on the rates of survive and growth, productivity and chemical composition of Asian seabass stocking in fresh water. A total 750 seabass fingerlings of 18.2 g were randomly located to 5 dietary treatments with 5 replicates named: CT, in which fish were fed a basal diet; DL and FL, in which fish were fed 100% dried or 100% fresh larvae; CT-DL and CT-FL, in which fish were fed 50% (as DM) of basal diet and 50% dried larvae or 50% fresh larvae, respectively. Results showed that the survival rates were not different between treatments, growth performance and yield highly improved by feeding basal diet and fresh larvae at 1:1 ratio; and chemical composition of fish fillet was similar among the treatments. However, the growth performance and yield of fish fed dried larvae were impaired.
Keywords: fresh water seabass farming, fish fillet, growth in weight and in length
In Viet Nam, seabass (Lates calcarrifer Bloch, 1790) is one of the important commercial fish species widely cultured because seabass has a fast growth rate, good adaptability to cage, net and pond culture in fresh, brackish and salt-water areas (Khanh et al 2010; Lan et al 2022ab; Tu et al 2023). The adult seabass is considered an insatiable carnivore but juveniles are omnivorous and opportunistic predatory species, with ontogenetic dietary progression from crustacean to fish. In present practice, seabass fingerlings are mainly fed by trash fish or floating pellets with high fish meal.
In order to partly replace fishmeal in seabass diets, black soldier fly larvae (BSFL) are considered as a good quality protein feed in aquaculture (Hoa and Dung 2016; Ngoan et al 2021; Lan et al 2022ab; Manh et al 2023, 2024; Suong et al 2023; Nghia et al 2023ab). Lan et al (2022b) recommended that BSFL fed by tofu by-product could be collected at 7-9 days after rearing at temperature 30-35°C and used as sources of protein and essential fatty acids. Many present studies showed that the use of fresh or dried larvae or larval meal in diets can improve aquatic animal performance at an appropriate level inclusion. Hoa and Dung (2016) have shown the growth rate of snakehead fish (Chana micropeltes) fed directly BSFL or 30% of BSFL meal-based diet was improved.
Manh et al (2023) reported that replacing fishmeal by BSFL at level of up to 12.9% did not affect the survival rate, growth rate and yield as well as chemical composition of snakehead fish but higher levels declined the growth performance and yield. Similarly, Suong et al (2023) concluded that inclusion of up to 9.2% BSFL meal in diets improved growth performance of climbing perch fish.
In addition, Nghia et al (2023a) reported that Thai frogs were fed the diet comprised equally from fresh BSFL and commercial feed increased growth performance as compared to diets with either fresh or dried BSFL. Manh et al (2024) reported that the inclusion of fresh BSFL in diets for the snakehead fish did not affect the survival rate, improved growth performance and yield; and did not affect the chemical composition of the fish. Suong et al (2024) concluded that the growth performance, yield and chemical composition of square-head climbing perch were improved by feeding commercial feed and fresh larvae at ratio 1:1.
In previous experiment, Lan et al (2022a) indicated that, the survival rate of Asian seabass fingerlings cultured in fresh water was higher than in brackish water and productivity was not affected by the water source (fresh and brackish) but it was higher in fish fed trash fish than in the one fed BSFL. The authors concluded that, replacement of total trash fish by fresh BSFL declined the productivity of seabass in both fresh and brackish water environment.
This study therefore aimed to evaluate the effect of the inclusion of fresh or dried black soldier fly larvae in diets on survive rate and growth, productivity and chemical composition of Asian seabass stocking in fresh water.
This experiment was carried out at the Lab of Faculty of Fisheries, Hue University of Agriculture and Forestry (HUAF), Hue City, Viet Nam.
Fish fingerlings: Seabass fingerlings of around 18.2g live weight were purchased from Quoc Thang Company, Hue city, Viet Nam. They were stocked in 10‰ salinity water in 1m3 composite tanks, and behaved to fresh water for one week for adaptation by lowering salinity by 3‰ per day until 0‰ salinity.
Larvae: Black soldier fly larvae were fed by tofu by-products and collected at day 7-9th after rearing (Lan et al 2022b). Larvae were washed with water several times to remove all impurities, soaked in boiling water for 15 minutes to kill them, then removed and drained. They were divided into two parts: one for drying at 60°C for 48 hrs (dried larvae) and another fresh larva stored at refrigerator for using in the experiment.
Their chemical composition was presented in Table 1.
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Table 1. Analyzed chemical composition of fresh and dried black soldier fly larvae (% feed) |
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|
Dry matter |
Crude protein |
Ether extract |
Crude fiber |
Ash |
|||
|
Dried larvae |
90.1 |
49.1 |
18.2 |
9.9 |
7.7 |
||
|
Fresh larvae |
21.4 |
12.5 |
4.1 |
2.3 |
1.9 |
||
All ingredients were carefully mixed according to their proportion 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 24hrs and stored in plastic bags at room temperature prior to use. The proportion of ingredients and the nutritive value of the diet are presented in Table 2.
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Table 2. Ingredient proportion and nutritive value of the control diet |
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|
Ingredient |
g |
|
|
Fishmeal |
460 |
|
|
Corn meal |
70 |
|
|
Soybean meal |
339 |
|
|
Soya oil |
21 |
|
|
Moller’ Tran fish oil |
30 |
|
|
Meizan wheat meal |
30 |
|
|
Premix vitamin and mineral |
30 |
|
|
CMC# |
20 |
|
|
Total |
1.000 |
|
|
Nutritive value |
% as DM |
|
|
Dry matter |
92.8 |
|
|
Crude protein |
43.8 |
|
|
Ether extract |
10.8 |
|
|
Crude fiber |
4.2 |
|
|
Total ash |
11.9 |
|
| #CMC: Carboxyl methyl cellulose | ||
A total 750 seabass of 18.2 g were randomly located to 5 dietary treatments with 5 replicates. In CT treatment (Control), fish were fed a control diet formulated of fishmeal and soybean meal as main protein source (Table 2). In DL and FL treatments, fish were fed 100% dried or 100% fresh larvae, respectively. In CT-DL and CT-FL treatments, fish were fed as DM 50% of control diet and 50% dried larvae and 50% fresh larvae, respectively. In each replicate, 30 fish were kept in a plastic tank of 200 L, and were daily fed by two meals at 8-9h and 16-17h.
The experiment was lasted 90 days. The layout of dietary treatments was presented in Table 3.
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Table 3. Dietary treatments |
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Treatment |
CT |
DL |
FL |
CT-DL |
CT-FL |
|
Feed/Diet |
Control |
Dry larvae |
Fresh larvae |
Control and dry larvae at 1:1 as DM |
Control and fresh larvae at 1:1 as DM |
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Replicates: 5, Number of animals per replicate: 30 |
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Water quality: Water temperature (°C) was measured by thermometer, pH by HI98107/Hanna handheld meter; NH 3 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). All water quality parameters were measured periodically every 2 days and measured at twice per day (7:00 and 14:00h).
Survival rate (SR, %): The SR is calculated by a ratio between survival fish number at the end (N1) and at beginning (N0) of the experiment.
SR (%) = (N1/N0) x 100
Growth performance: Every 15 days of experimental implementation, the weight and length of 10 fish/tank were measured to calculate the following parameters:
Daily weight gain (g day-1) was a ratio between total weight gain within a stocking time and days of stocking.
Specific growth rate in weight (SGRw, % day-1) = [Ln(final weight) - Ln(initial weight)/ duration in days] x 100
Specific growth rate in length (SGRl, % day-1) = [Ln(final length) - Ln(initial length)/ duration in days] x 100
Feed conversion ratio (FCR) = total feed intake (kg)/total weight gain (kg)
Fish yield (Y, kg/m2): The Y is total fish weight at the end of the experiment and calculated by the survived fish number multiplied individual live weight for 1 m2 water surface.
Chemical composition of fillet: At the end of the experiment, the samples of fish fillet were taken from 5 fish/tank for chemical analysis.
All feed samples and fillet were chemically analyzed for dry matter (DM), ether extract (EE), crude fiber (CF), and total ash according to the procedures of AOAC (1990). Samples were analyzed at the Lab of the Faculty of Animal Science and Veterinary Medicine, HUAF.
The data were statistically processed by analysis of variance (ANOVA) by General Linear Model in Minitab v.16.2 (2010) and presented in the form of the mean (M) and standard error of the mean (SEM). The difference between the mean values was determined by the Tukey method at a confidence level of 95%.
Water quality parameters such as temperature ranged 28.21-28.48oC in AM and 28.43-28.90oC in PM, pH (7.11-7.18 in AM and 7.34-7.44 in PM), NH 3 (0.06-0.07 in AM and 0.08-0.09 in PM mg/L) DO (4.62-4.69 mg/L in AM and 4.77-4.81 mg/L in PM) and was similar among treatments.
The survival rates in the recent study range 75.56-84.44% (Fig. 1) are not different between the treatments (p>0.05). No difference in the survival rate proves that the seabass fingerlings could utilize 100% fresh or dried BSFL. In general, the survival rate of seabass fingerlings is low and is affected by many factors, such as growth stage, feed and feeding systems, nutritive value of diet, etc. Khanh et al (2010) found the survival rates of seabass fingerlings of 5-6 g live weight fed five different feed types (trash fish, golden snail, pellets and their combinations) ranged 14.5-40% at 6-old weeks and were highest in fish fed trash fish. Tu et al (2023) reported that the survival rates of seabass fingerlings of 20-25 g live weight stocked in 15 - 20‰ salinity were ranged 81.1-93.3% and wasn’t affected by gradually included 0.5-2% of fresh BSFL in the diet. Similarly, in the study on replacing totally trash fish by fresh BSFL, Lan et al (2022a) observed that the survival rates of seabass fingerlings were not different between two dietary treatments. In addition, Manh et al (2024) and Suong et al (2024) have found no effect on survival rate of snakehead fish and square-head climbing perch fed fresh or dried larvae or diets with combination of the larvae and commercial feed.
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| Figure 1. Survival rate of fish at 90-old days fed different diets |
After 90 days of feeding, live weights of fish fed different diets has been changed and presented in Fig. 2 and 3, and Table 4.
 |
| Figure 2. Live weight of fish fed different diets at 90-old days |
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Table 4. Growth performance of fingerlings fed different diets |
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|
Item |
Treatment# |
SEM |
p -value |
|||||
|
CT |
DL |
FL |
CT-DL |
CT-FL |
||||
|
Initial weight (g) |
18.3 |
18.1 |
18.2 |
18.2 |
18.2 |
0.049 |
0.21 |
|
|
Final weight (g) |
164.7ab |
129.5d |
157.9bc |
135.3cd |
189.3a |
5.251 |
<0.001 |
|
|
Daily weight gain (g/d) |
1.63ab |
1.24d |
1.55bc |
1.30cd |
1.90a |
0.058 |
<0.001 |
|
|
SGRw (%/d) |
2.44ab |
2.19d |
2.40bc |
2.22cd |
2.60a |
0.037 |
<0.001 |
|
|
Initial length (cm) |
11.5 |
11.2 |
11.4 |
11.3 |
11.3 |
0.065 |
0.41 |
|
|
Final length (cm) |
22.0ab |
20.7b |
21.3ab |
20.6b |
22.9a |
0.379 |
0.01 |
|
|
Daily length gain (cm/d) |
0.12ab |
0.11b |
0.11ab |
0.10b |
0.13a |
0.004 |
0.02 |
|
|
SGRl(%/d) |
0.72ab |
0.68b |
0.69b |
0.67b |
0.78a |
0.019 |
0.02 |
|
|
FCR |
1.69b |
1.93a |
1.77ab |
1.76ab |
1.58b |
0.040 |
0.00 |
|
|
Yield (kg/m2) |
10.44b |
7.99c |
8.95bc |
8.35bc |
11.05a |
0.468 |
0.01 |
|
|
# CT: Control diet; DL: dried larvae diet; FD: fresh larvae diet; CT-DL: control and dry larvae (1:1); CT-FL: control and fresh larvae (1:1) abcd: Means in the same row without common letter are different at p<0.05 |
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At the time of harvesting, live weight of fish fed different diets ranges 129.5-189.3 g and is statistically difference between treatment (p<0.05). The live weight of fish in the CT-FL (in diet composed from control diet and fresh larvae) is highest and lowest in the DL- dried larvae (p<0.05). Similarly, the daily weight gain (DWG) ranged from 1.24-1.9 g/day was different between the treatments (p<0.05) and reached a highest value in the CT-FL and a lowest value in DL. The results of specific growth rate by weight (SGRw) also showed similar results to DWG, and the SGRw value ranged 2.19-2.6 %/day. The FCR ranged 1.58-1.93 and was lower in the CT-FL and CT than in DL (p<0.05). The productivity of fish fed control diet and fresh larvae was highest in the CT-FL (11.05 kg/m2) and lowest in DL (7.99 kg/m2). However, the productivity of fish ranged 7.99-8.95 kg/m2 in DL, FL and CT-DL was similar (p>0.05).
In addition, the results showed that final length of fish ranged 20.7-22.9 cm after 90 days stocking in fresh water. The final length values were different between treatment (p<0.05), were higher in the CT-FL (22.9 cm) than in DL (20.7 cm). Similarly, the daily length gain (DLG) and special growth rate in length (SGRl) of fish also showed higher results in CT-FL than in DL (p>0.05).
In this study, the growth performance, productivity and feed cost were improved in seabass fingerlings fed the control diet plus fresh larvae (1:1 ratio as DM), meanwhile were impaired in fish fed dried larvae. These findings are in agreement with conclusions reported by Manh et al (2024) and Suong et al (2024), who reported that the inclusion of fresh BSFL in commercial feed for the snakehead fish and climbing perch improved feed conversion ratio, increased live weight and daily weight gain and fish’s yield. These findings suggest that farmers should feed snakehead fish and climbing perch with commercial feed plus fresh black soldier fly larvae to maintain good condition factor and enhance fish growth performance and production.
Better growth performance and yield in fish fed fresh larvae and control diet probably resulted from a diet rich in essential fatty acids in fresh BSFL. Lan et al (2022b) reported that BSFL fed by tofu by-products contained very high LA (omega-6) ranging from 27.57 - 29.7% and ALA (omega-3) ranged from 1.89 - 2.04 % as total fat. Also, it relates to the habit of seabass fingerlings, who prefer catching fresh insects rather than dry one. In fact, we observed that fingerlings slowly couth the dried BSFL.
 |
| Figure 3. The length of fish fed different diets at 90-old days |
In general, feeding seabass with a combination of basal diet and fresh black soldier fly larvae at 1:1 as DM ratio improved significantly growth rates in weight and length and the productivity, meanwhile feeding dried larvae to seabass reduced growth performance and productivity, possibly due to the dry larvae form made it difficult for digestion and utilization.
Results on chemical composition of fish fillet in Table 5 showed that except for ether extract (EE) content, all items were not different between the treatments (p>0.05). The EE content tended to higher in the CT-FL, CT and FL than in DL, but this value in DL and CT-DL was not statistical different (p>0.05).
|
Table 5. Analyzed chemical composition of fish fed different diets (% as fresh fillet) |
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|
Item |
Treatment |
SEM |
p -value |
|||||
|
CT |
DL |
FL |
CT-DL |
CT-FL |
||||
|
Dry matter |
25.8 |
25.5 |
25.2 |
25.5 |
25.4 |
0.182 |
0.38 |
|
|
Crude protein |
16.2 |
16.1 |
16.1 |
16.2 |
16.3 |
0.102 |
0.40 |
|
|
Ether extract |
4.19ab |
3.51c |
4.23ab |
3.64bc |
4.50a |
0.123 |
0.002 |
|
|
Total ash |
3.75 |
3.91 |
3.76 |
3.89 |
3.70 |
0.092 |
0.46 |
|
Manh et al (2024) reported that proximate composition of fillet meat at the end of the experiment, including the contents of DM, CP, EE and ash was not affected by the inclusion of fresh or dried BSFL in the diets’ snakehead fish. However, Suong et al (2024) found the effect of inclusion of fresh or dried BSFL in diets of climbing perch on EE content of fillet. The EE contents of fish fed fresh larvae and fresh larvae plus commercial feed were higher than in fish fed dried larvae and commercial feed. However, the EE content did not tend to decrease in rainbow trout when replacing 26.4% fishmeal with larvae meal (Dumas et al 2018); in yellow catfish with replacement rates up to 100% (Xiao et al 2018).
Feeding fresh or dried larvae or combination of larvae and control diet to seabass fingerlings stocked in fresh water didn’t affect the survival rates but the growth performance and yield highly improved by feeding control diet and fresh larvae at 1:1 ratio. However, the growth performance and yield of fish fed dried larvae were impaired.
This work was supported by Hue University under the Core Research Program, Grant No. NCTB.DHH.2025.14.
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