2.1. Ethical statement
This study was conducted based on the approval by the ethical committee of TNJFU, Nagapattinam, Tamil Nadu, India.
2.2. Experimental fish and feeding trial
Gold fish juveniles were procured from Ornamental Fish Trade Centre, Kolathur, Chennai, Tamil Nadu, India. Ostensibly, healthy seeds in the first instance were acclimatized in fibre-reinforced plastic tanks by feeding them with diet containing 320 g/kg of protein over a period of three weeks. Before the experiment, the fishes were graded to select an individual average weight of 2.8 ± 0.3 g and were stocked in indoor aquarium facility. Three hundred and sixty fishes were distributed in 18 groups with twenty fishes in each aquarium. The aquarium had a water holding capacity of 70 litres in which the fishes were stocked for the feeding trial. Satiation feeding was carried out twice a day (09.00 and 17.00 H) for 60 days and the daily feed consumption was noted. Water exchange was carried out at the rate of 10% every three days in each aquarium. Aeration was continuously provided throughout the experimental period using a 5-HP air blower (Everest Pvt). During the growth trial, water quality parameters were monitored daily and the mean values were as follows: water temperature at 30.96±0.54°C, pH at 8.22±0.07, dissolved oxygen at 6.64±0.61 mg/L, ammonia-N at 0.07±0.10 ppm, nitrite-N at 0.76±0.44 ppm, nitrate-N at 0.06±0.10 ppm and hardness at 408.51±68.64 ppm.
2.3. Experimental diets
Six different FM and BSFLM based isonitrogenous experimental diets were formulated to contain 320 g/kg of crude protein (Table 1). The experimental diets were supplemented with black solider fly larvae meal (Eco care Agrovet) at levels of 0.0 (T0), 6.7 (T20), 13.4 (T40), 20.1 (T60), 26.8 (T80) and 33.5 g/kg (T100) to replace fish meal protein at 0, 20, 40, 60, 80 and 100 percent, respectively. The experimental diet T0 was observed as a control diet with 20 g/kg inclusion of fish meal and excluding the addition of BSFLM. The inclusion level of palm oil was adjusted to maintain isolipidic nature of experimental diets. Dietary ingredients were finely ground, thoroughly mixed using vertical ingredient mixer (Jinan Sunpring Machinery) and then extruded at 60–70°C to prepare 1.5-mm floating pellets using a single screw extruder (Unitech). The air tight plastic containers were utilized to store all the experimental diets at room temperature.
TABLE 1: Formulation and chemical composition of the experimental diets (g/kg of diet)
Ingredients
|
T0
|
T20
|
T40
|
T60
|
T80
|
T100
|
Black soldier fly larvae meal a, f
|
0
|
67
|
134
|
201
|
268
|
335
|
Fish meal b
|
200
|
160
|
120
|
80
|
40
|
0
|
Soybean meal b
|
270
|
270
|
270
|
270
|
270
|
270
|
Groundnut oil cake b
|
80
|
80
|
80
|
80
|
80
|
80
|
Corn flour b
|
266
|
246
|
226
|
206
|
185
|
165
|
Rice bran b
|
100
|
100
|
100
|
100
|
100
|
100
|
Cassava starch b
|
30
|
30
|
30
|
30
|
30
|
30
|
Palm oil c
|
34
|
27
|
20
|
13
|
07
|
0
|
Dicalcium phosphate b
|
10
|
10
|
10
|
10
|
10
|
10
|
Vitamin premix d
|
5
|
5
|
5
|
5
|
5
|
5
|
Mineral premix e
|
5
|
5
|
5
|
5
|
5
|
5
|
Proximate composition (g/kg dry matter)
|
Crude protein
|
329.4
|
322.8
|
325.7
|
323.2
|
320.9
|
323.4
|
Crude lipid
|
70.1
|
71.2
|
71.6
|
70.4
|
71.1
|
70.9
|
Crude fibre
|
32.2
|
33.6
|
33.8
|
33.7
|
33.9
|
33.8
|
Ash
|
83.9
|
83.5
|
84.3
|
83.6
|
83.4
|
83.8
|
aEco care agrovet, Puducherry, India
bNational co-operative consumers ‘federation of India, Chennai, India
cLocal market, Chennai, India
dComposition of vitamin premix (quantity/kg): Vit. A—10,000,000 IU, Vit.B1—5,000 mg, Vit.B2—5,000 mg, Vit.B3—6,000 mg, Vit.B5—6,000 mg, Vit.B6—6,000 mg, Vit.C—60,000 mg, Vit.D3— 2,000,000 IU, Vit. E—10,000 EU, Vit. H—200 mg.
eComposition of mineral premix (quantity/kg): magnesium—2,800 mg, iodine—7.4 mg, iron—7,400 mg, copper—1,200 mg, manganese—11,600 mg, zinc—9,800 mg, chlorides cobalt—4 mg, potassium—100 mg, selenium—4 mg, calcium carbonate—27.25%, phosphorous—7.45 mg, sulphur—0.7 mg, sodium—6 mg, Calpan—200 mg, aluminium—1,500 mg and choline chloride— 10,000 mg
fProximate of BSFLM – crude protein-42.27 %, crude lipid-18%, crude fibre- 8.73%, ash- 24.16%, moisture- 20.3%
|
2.4. Fish growth sampling
After 60 days of feeding trial, all the fish were put down with an overdose of tricaine methane sulphonate (MS-222; Sigma-Aldrich) and individually counted and weighed to estimate their survival, feed conversion ratio (FCR), protein efficiency ratio (PER), Thermal-unit growth coefficient (TGC) as follows:

2.5. Proximate and amino acid analysis
Six fishes from each experimental unit were collected after completion of growth trial to determine whole-body composition. The proximate composition such as moisture, crude protein, crude lipid and ash contents of experimental diets as well as whole body was estimated following standard protocols (AOAC, 2010). The amino acid composition of control and treatment diets were estimated using ultra-pressure liquid chromatography (UPLC; Model—Waters ACQUITY-UPLC, Waters), following the method described by Ishida et al. (1981).
TABLE 2: Amino acid composition of the experimental diets (g/kg of diet)
|
T0
|
T20
|
T40
|
T60
|
T80
|
T100
|
Essential amino acids
|
|
Arginine
|
25.6
|
25.2
|
24.9
|
23.6
|
23.2
|
23.4
|
Histidine
|
12.5
|
11.7
|
11.8
|
12.4
|
12.6
|
12.5
|
Isoleucine
|
18
|
17.4
|
17.5
|
18.6
|
18.3
|
18.1
|
Leucine
|
26.1
|
25.8
|
25.5
|
25.7
|
26.1
|
25.6
|
Lysine
|
19.5
|
19.3
|
19.2
|
18.8
|
18.6
|
18.3
|
Methionine
|
5.9
|
5.7
|
5.4
|
5.2
|
5.2
|
50.1
|
Phenylalanine
|
18.8
|
19.2
|
19.4
|
18.7
|
18.4
|
18.7
|
Threonine
|
14.6
|
14.3
|
14.5
|
14.2
|
14.1
|
14.1
|
Tryptophan
|
3.1
|
2.8
|
2.7
|
2.4
|
2.3
|
2.4
|
Valine
|
19.6
|
19
|
19.1
|
19.5
|
19.4
|
19.6
|
Non-essential amino acids
|
|
Cysteine
|
5.3
|
5.4
|
5.4
|
5.2
|
5.3
|
5.1
|
Tyrosine
|
13.3
|
13.5
|
13.5
|
13.3
|
13.3
|
13.3
|
Glutamic acid
|
61.7
|
63.1
|
64.6
|
65.2
|
66.1
|
66.6
|
Aspartic acid
|
43.4
|
43.2
|
42.7
|
46.4
|
44.8
|
44.4
|
Glycine
|
19.5
|
19.5
|
19.5
|
20.7
|
20.3
|
20.2
|
Serine
|
18.2
|
18.2
|
18.3
|
18.6
|
18.5
|
18.6
|
Alanine
|
18.8
|
17.2
|
17.4
|
17.8
|
18.5
|
19
|
2.6. Haemato-biochemical assay
The blood samples were obtained from three individual fishes from each replication of aquaria to analyze the hematological and serum biochemical parameters at the end of the feeding trial. The fishes were anaesthetized using clove oil before collection of blood and caudal vein puncture method was used to obtain blood using 1-ml syringe. The collected blood samples were expelled into heparinized and non-heparinized tubes and stored immediately on ice. The serum was obtained by keeping the non-heparinized tubes in slant position for 2 hours and then centrifugation at 3,500 rpm for 25min at 4°C in a refrigerated centrifuge (Eppendorf Centrifuge 5804 R) was done. Neubauer hemocytometer was used to determine the RBC (red blood cell) counts. Cyanmethemoglobin method (Drabkin, 1946) was used to analyze the haemoglobin (Hb) contents whereas the microhematocrit method (Nelson & Morris, 1979) was used to determine the hematocrit (Ht). Erythrocyte indices, such as MCH, MCV and MCHC were calculated according to the equation given by Wintrobe (1934). The equations are as follows:
MCV (per µl) = (Ht × 10)/erythrocytes
MCH (%) = (Hb × 10)/erythrocytes
MCHC (g/dl) = (Hb × 100)/Ht
The total serum protein was analysed following the Biuret method (Reinhold, 1953). The bromocresol green binding method (Doumas et al., 1971) was utilized to calculate the albumin content. The globulin value is derived by deducting the albumin values from the total serum protein. A/G ratio is calculated by dividing the albumin value and globulin value. The method of Parekh and Jung (1970) was followed to calculate Serum cholesterol (CHO). Triglyceride (TG) levels were estimated following the protocol of Rice (1970).
2.7. Digestive enzyme analysis
At the end of the feeding trial, three fish (n=3 triplicate per treatment) from each treatment were randomly selected, and intestine samples were collected by dissecting it on chilled condition. The sample was then homogenized with cold phosphate buffer (pH 7.8) and centrifuged at 4500 rpm for 5minutes. The supernatant was kept at -20°C until the enzyme assay was carried out.
Quantifying of amylase activity was fulfilled using 3.5 dinitro salicylic acid colorimetric technique based on the method illustrated by Clark (1964). Cherry and Crandel (1932) method was used to determine the lipase activity by measuring the fatty acid release caused by enzyme hydrolysis of olive oil. The protease activity was quantified using Lowry, Rosebrough and Farr technique. The enzyme activity was observed based on the changes in absorbance using a spectrophotometer (Lamba 25UV Win Lab V 6.0). One unit of enzyme activity was expressed as 1µg of maltose, fatty acid and tyrosine released per minute.
2.8. Quantitative real-time PCR (qRT-PCR)
Sequentially, after the end of the feeding trial, the skeletal muscle (for MyoD and myostatin gene) and pituitary gland (for GH gene; n = 3 fish per aquaria) was collected to extract the total RNA as per the manufacturer’s instruction using RNA iso-plus (Takara Bio). Then, 2g of total RNA was reverse-transcribed to cDNA according to the manufacturer's instruction. The protocols of Prabu et al. (2021) were utilized for relative gene expression studies. The gene-specific primers of MyoD, myostatin, 18sRNA, GH gene and β actin were shown in Table 3. The quantitative real-time-polymerase chain reaction (qRT-PCR) consisted of 20 ng of cDNA template, 10 μM of each primer (forward and reverse), and 1× SYBR Green PCR Master Mix Kit (Takara Bio), in a 20 μL of total volume. The qRT-PCR was performed in a C1000 Touch thermal cycler-CFX96 Real-time PCR (Bio- Rad). The PCR cycling profiles were carried out programmed with an initial denaturation at 95°C for 10 min, along with 40 cycles of 15 s denaturation at 95°C, annealing at 60– 62°C (depends on the target genes) for 30 s, extension at 72°C for 30 s and ended with dissolution curve. The threshold cycle values of the qRT-PCR performed in triplicates were calculated and from that the relative expression level of specific gene was presented as 2−ΔΔCt (Livak & Schmittgen, 2001). The genes 18S rDNA and β-Actin were utilized as an internal control gene to collate the relative expression levels of the genes.
TABLE 3: Primers used for qRT-PCR analysis
Gene name
|
GenBank number
|
Primer sequence (5´-3´)
|
Myogenic Factor (MyoD)
|
GU246722
|
Forward: CCACCTGTCAGACAACCAGA
Reverse: ACTGCGTTCGCTCTTCAGAC
|
Myostatin 1
|
FJ972683
|
Forward: TCCACATGACCCTGCAGAC
Reverse: TGCACCACACATACTCCTCATC
|
18Sribosomal
DNA (18SrDNA)
|
JF698683
|
Forward: GGACACGGAAAGGATTGACAG
Reverse: GTTCGTTATCGGAATTAACCAGAC
|
Pituitary growth hormone
|
XM_003442542
|
Forward: TCGGTTGTGTGTTTGGGCGTCTC
Reverse: GTGCAGGTGCGTGACTCTGTTGA
|
β-Actin
|
EU887951.1
|
Forward: CCACACAGTGCCCATCTACGA
Reverse: CCACGCTCTGTCAGGATCTTCA
|
2.9. Statistical analysis
All the experimental data were shown as the mean values ± standard deviation (SD) of three replications. Each and every data were tested for normality (Shapiro–Wilk test) and homogeneity of variance (Levene’s test) and transformed when the data did not show normal distribution. One-way ANOVA was performed to test the significant differences, wherein the Tukey's test was used to find out the significant differences between experimental groups. Differences were considered significant at p < 0.05. The software SPSS 20.0 for windows (SPSS) was used to statistically analyze the data.