1. Introduction
Pangasius catfish is an important commercial aquaculture species with a high economic value for fish farming with an annual production of approximately reached 1.52 million tonnes [
1]. Recently, it is reported that the low survival rate and unstable supply of fish fingerlings throughout the year could be one of the major hindrances and bottlenecks for the continued growth of the
Pangasius aquaculture industry sector in the Mekong Delta, Vietnam [
2,
3,
4].
Pangasius broodstocks spawn all year round, but it has low and variable survival rates for fish fry and fingerling, rarely reaching over 20–25% during the main spawning season and only 12–15 % end-breeding season [
2,
4,
5,
6,
7]. In the Mekong Delta, Vietnam, most
Pangasius catfish hatchery operations and nursery farming typically feed their broodstock fish with the same commercial diet as used for grow out of the produced commercial fish. This diet, containing 28–30% available crude protein (CP) and 3.5–5% lipid contents, may not contain the appropriate feed nutrient levels to optimize spawning success of brooders and to improve the quality of fish fry [
4,
5,
8,
9]. Many scientific researchers stated that low quality broodstock nutrition, feeding, and feed management is one of the major challenges for fish producers, alongside decreased genetic integrity, inbreeding of fish, and seed degeneration [
3,
4,
7,
10,
11,
12]. However, many research scholars emphasize that better quality broodstock diets, formulated to increase successful reproduction and better fish management practices, would allow producers not only to reduce the number of broodstock needed to meet eggs and fry production goals but also produce better quality fry and meet fry demands of fish farmers’ year round [
13,
14,
15,
16].
Many studies are being carried out around the world to investigating the human health benefits of fungi and algae [
17,
18,
19]. Several species of algae and fungi including lichenized fungi (lichens), have the ability to biosynthesize biologically active compounds and are potential sources of natural antibiotics and antioxidants that could be used as supplementary medicine and food sources for human and aquatic animals [
58]. The main nutrients found in mushroom-fruiting bodies are proteins, carbohydrates, fats, including essential fatty acids (EFA), fibre, and vitamins and minerals. Algae biomass and lichens are a renewable source of many valuable active substances that have a wide range of applications in many industries, such as food, chemical, agriculture (including animal and aquatic feeds), pharmaceuticals, cosmetics, and medicines [
17,
18,
20]. Microalgea provides essential amino acids, valuable triglycerides such as lipids, vitamins, and pigments, making them suitable as nutritional supplements in animal feed and aquafeed formulations [
17,
18,
21,
22]. It is also reported that microalgea supplements in diets improved the fatty acid profile of farmed fish and shrimp by improving the ω-3/ω-6 ratio, increasing polyunsaturated fatty acid (PUFA) content, and enriching long chain PUFAs [
21,
23]. Studies on application of microalgae species rich in EPA or DHA in aquaculture include Pacific white shrimp, Giant tiger prawn, Giant freshwater prawn [
21,
24,
25], Gibel carp [
23], Tilapia [
22,
25], European seabass [
26], and Common carp [
25]. Several studies reported that microalgae oils have the potential to replace fish meal and fish oils in aquaculture and ensure sustainability standards. It can be used directly as supplement sources in animal feed and aquafeed feed formulations to improve reproduction, produce good quality of fish eggs, fish fry and yields [
18,
22,
27].
In recent years, dietary protein, lipid (fats, fatty acids), vitamin and energy requirements of many commercial catfish species (included Channel catfish, Black catfish, Bagrid catfish, African catfish have been widely examined [
28,
29,
30,
31,
32,
33,
34,
35,
36,
37,
38,
39], while studies focusing specifically on broodstock nutrition of
Pangasius catfish species are still limited. This absence of research may be because it is generally considered to be of high cost as it requires a long period of feeding broodstock fish before any effects can be seen on fish fecundity, egg quality, hatching success [
13,
14,
15]. The quality of feed ingredients, feed quality and feed utilization by broodstock fish species is a key factor to improve the reproductive performance, egg and sperm quality and hatchability and enhanced survival rate of fish species [
13,
14,
15]. The quality of feed ingredients, feed quality and feed utilization by broodstock fish species is a key factor to improve the reproductive performance, egg and sperm quality, hatchability and enhanced survival rate of fish species [
13,
14,
15]. Up to now little research is available on broodstock nutrition and the potential effects on reproductive performance, fish fry survival rate fry, and fingerling and seed quality from adding vitamins, fatty acids from algae oil and fungi oil to the food of
Pangasius catfish broodstock. A study on striped catfish in Vietnam recommended that a standard for the conditioning feeds of
Pangasius catfish broodstock needs to be developed [
40]. Therefore, this feeding trial was conducted to evaluate the effects of different diets supplemented with vitamin solution effect on growth performances, broodstock reproduction, hatchability, and the survival rates of fry and fingerling of
Pangasius catfish. The hypothesis tested in this study was that a dietary of approximate 35% CP contents supplemented with different vitamin solution, and plant oils (algal oil, and fungal oil) can improve the reproductive performances, eggs quality of broodstock, and enhance the survival rates of fry and fingerlings of
Pangasius catfish. The findings of this research will provide valuable information for
Pangasius catfish farmers and the fish production industries in the Mekong Delta, Vietnam.
2. Materials and Methods
2.1. Study Site and Research Layout
The experiments were carried out at the Pangasius catfish broodstock farm and hatchery in My Thoi wards, Long Xuyen city, An Giang province, Vietnam. Two experiments were carried out, one outdoors and one indoors. In the outdoor experiment, 180
Pangasius catfish brooders were fed six test diets supplemented with differing amounts of vitamin premixes, algal oil, and fungal oil in a series of 18 hapa nets in an earthen pond of 1,500 m
2, with three replicates for each diet. The experiment was done during October–February, which is over spawning season. The experiments of breeding, larvae rearing and fingerling rearing were conducted in an indoor hatchery. These experiments aimed to evaluate the quality of eggs, egg hatchability, growth performances, fingerling production, and the survival rates of fingerlings of
Pangasius catfish. The research layout of this study is presented in
Figure 1
2.2. Pond Preparation and Management of the Broodstock
The earthen pond used for the broodstock experiment was prepared by pumping out the water and treating it with 150 kg lime (CaCO3). After this the pond was filled with new freshwater from a reservoir pond. A system of 18 hapa-nets with 4.0 mm mesh size were used to test six treatments in triplicates. Each hapa-net was suspended and tied to four Melaleuca poles. The sides and bottoms of each hapa-net were scrubbed and cleaned every two months, and at least 20–30% of the water was exchanged monthly during cultivation of the broodstock fish.
2.3. Selection Criteria of Broodstock
The broodstock were obtained from a broodstock fish pond at the Pangasius catfish farm of NAVICO. A total of 180 brooders fish at the pre-maturation stages, which were at 3–3.5 years old, were selected from the broodstock fish pond and transferred to 18 hapa-net system (6 treatments in triplicates), where each hapa-net was 3.5 m x 3.5 m x 3.0 m (length x width x depth) (
Figure 1). At the beginning of the experiments the body weight, length and belly width of the broodstock fishes were measured. The female breeders were checked and selected based on having a large soft belly, healthy external appearance, good agility condition, and uniform eggs size. The male breeders were selected based on the thickness of the milt/semen, obtained by hand stripping, healthy external appearance, good agility condition, and large size [
41].
2.4. Experimental Diet Preparation and Feeding Practice
The experimental diets were formulated to meet the nutrient requirements for striped catfish broodstock, with approximately 35% CP supplemented with vitamin premix, algal and fungal oils (
Table 1). The experimental feed ingredient sources were: soybean meal (45% CP) and Kien Giang fish meal (55% CP), poultry by-product meal (65% CP), and soybean oil, which were purchased from the local markets in An Giang and Dong Thap provinces. Fish oil (Tuna oil), choline chloride (50% choline), mineral premix for fish, vitamin premix algal oil and fungal oil were provided by DSM SINGAPORE INDUSTRIAL PTE. LTD.
The detailed composition of vitamin premix, mineral premix and algal oil compounds are presented in
Table 1. Two tonnes of floating pelleted feeds with 5.0 mm diameters of the six test diets of the experiment were produced at the Aquafeed production of Dong A plant, Cao Lanh city, Dong Thap province, Vietnam. The broodstock fishes were reared and fed with the experimental diets for 65 days. Broodstock fishes of each treatment were fed by hand to apparent satiety, at a rate of about 3–5% of body weight, twice a day at 8:00–9:00AM and 4:00–5:00 PM. The chemical composition of the test ingredients and diets are shown in
Table 2 and
Table 3.
2.5. Broodstock Experimental Design
The experiment was set up as a factorial design with six different diets fed in triplicate groups of Pangasius catfish broodstock cultured in a hapa net system in an earthen pond (1,500 m2) with a depth of about 2.5 m. Ten fishes with a mate ratio of 3 males : 7 females were reared in each net for about two months to acclimatize them to the conditions in the hapa net. Before the experiment began all the fish were fed daily on the same commercial diet, containing 24% CP. Feeding was carried by hand, from a small boat, between 4 and 5pm each day, at a rate of 3-5% of body weight, until fish reached apparent satiety. The feed was distributed to each treatment using a small boat.
2.6. Induced Spawning and Larvae Rearing Practices
2.6.1. Mature Broodstock Fish Selection for Induced Spawning
After 65 days of intensive feeding of the broodstock fish with the experimental diets, the egg quality and development status of individual female fish were checked with the help of a catheter. Mature females were identified by their big, round and soft bellies, along with reddish, swollen ventral genital pores. Male broodstock fish were identified by observation of their genital papilla, which oozes milt/semen when they were ready to breed, the presence of a slight stripe on the abdomen, and the quantity and quality of their sperm/milt were checked by stripping.
Mature male and female broodstock fish in good condition from each treatment were selected, marked, and quarantined for 1–2 days in separate rectangle tarpaulin tanks with 10 m3 of water volume for female breeders and 5 m3 of water volume for male breeders for their acclimation to the water environmental condition in the hatchery before the induced breeding procedure commenced
2.6.2. Induced Stripping Practices of Broodstock
The mature broodstocks were induced to spawn in hatcheries using human chorionic gonadotropin (hCG) injection. The female fish were given 4 injections, each injection with a different dose of hCG: 200, 300, 700 and 2,700 UI/kg, while male fish were injected only once, at the same time as the final injection for the females. The detailed protocol of hCG doses, time for fish injection, and injection dose calculation are given in the supplemental information. Females ovulated from 10–12 hours after the last injection, with a water temperature of 27–28°C. Eight hours after injecting the last dose of hCG, female breeders were checked for eggs by slight stripping on the belly to ensure that the ripe eggs were at stage IV condition. Eggs and milt/semen of fish breeders from each treatment were then drily striped and slowly poured into each other in small plastic tubs, each stripping into a separate tub. All eggs and body weight of each female from different treatments were weighed for their gonadosomatic index determination. Milt/semen and eggs of different treatment were stirred around two minutes by using the chicken feathers and then washed 2–3 times with clean water (
Figure 1). A tannin solution with 5% concentration was added to the tub to remove adhesiveness (stickiness). The mixture was slowly poured on the mixed eggs in a plastic tub of each treatment and stirred for 1–2 minutes, and then thoroughly rinsed with clean water 2–3 times. One gram of eggs of each treatment was sampled and measured in triplicate to evaluate the egg fecundity, eggs number, and eggs size, using a microscope (Carl Zeiss Microscopy, Germany) at 4x and 10x magnifications. The wet weight of eggs was determined using an electronic balance (Mettler Toledo, Swiss).
2.6.3. Eggs Incubation and Larvae Fish Nursing Practices
An incubator system was set up in a closed re-circulation system in a series of 18 hatching jars (Weiss-shaped incubators) for six treatments in triplicates with a water volume of about 18 L for each hatching jar (Fig. 1). The water supply for the hatching jars of the incubator system was taken from a reservoir tank, treated with a biological filter and passed through an ozone generator before being supplied to each hatching jar. The water flow through the incubator system had been adjusted to moderate flow so the eggs were stirred and not allowed to settle at the bottom of the jars. Fertilized eggs were stocked at an average density of 44,340 (15,800–88,890) eggs per hatching jar. The fertilized eggs of each treatment were incubated in the hatching jar system for 35–36 hours at a water temperature of 25–270C during December.
After hatching, all larvae fishes were moved and delivered into 18 different nursing tanks (six treatments in triplicates) with 0.5 m3 of water in each tank and reared for 48 hours. Aeration with two air-stone diffusers was provided to each tank via a moderate-pressure electrical blower. The total length and height of larvae after hatching were measured under a microscope (Carl Zeiss Microscopy, Germany), and the wet weight of hatchlings was measured using an electronic balance (Mettler Toledo, Swiss).
2.7. The Experiments of Larvae to Fingerling Rearing
The larvae remained in the nursing tanks for the first 48 hours, until the yolk sacs had been absorbed, and then transferred to larger indoor tanks for the next 15 days, during December 2020 to January 2021. There were 24 tarpaulin tanks, placed indoors, each tank with a water volume of 1 m3 (1 m x 1 m x 1 m for each tank) and a stocking density of 15,000 larvae/tank. They were supplied with water which had been treated with a biological filter. The experiments were covered by a blue tarpaulin and a green net for sun and rain shade to control the temperature during the winter season (
Figure 1). The rearing tarpaulin tanks of the experiment were also covered with a long white tarred canvas to maintain the water temperature at nighttime (Fig. 1, G). Two days after hatching and until the 5th-day, the larvae fishes was fed with Artemia (Vinh Chau Artemia products) at a rate of Artemia to larvae of 5 : 1. Between 6–15 days after hatching the larvae fishes were also fed a mixture made up of 50% brine shrimp + 50% of UV-milk powder feed with 42% CP content (Commercial feed powder (Name: Tomboy TB0). The larvae were fed daily 4 times to apparent satiety at 8.00 AM, 11:00 AM, 2:00 PM, and 5:00 PM. At the beginning of the experiment, a sample of 30 larval fish from the nursing tank from each treatment was weighed using a digital scale and measured using a microscope (Mettler Toledo, Swiss) for the evaluation of growth performances indices. All larvae fish from each experimental treatment were harvested, counted and weighted at the end of the experiments to estimate production and final survival rates of the fish.
The second experiment of fry to fingerling rearing was conducted after finishing and harvesting the fish larvae from first experiment. 2,000 fry per tarpaulin tank were reared for 45-day using the same facility, equipment and diet treatments (6 treatments in 4 replicates) as the first experiment of larvae rearing (Fig.1). Fish were fed 2 times per day with the experimental milled diets to apparent satiety at 8.00 AM and 5:00 PM. At the beginning and in the end of the experiment, a sample of 30 fish in each nursing tank from each treatment were weighed and measured in the same way as in the first experiment. Fish of each treatment during the experiment were collected every fortnight to measure weight and length gains for the evaluation of growth performances indices. All fry of each experimental treatment were harvested, counted and weighted at the end of the experiments to estimate fingerling production and final survival rates of fingerlings.
2.8. Water Quality Monitoring
Temperature (TºC), Dissolved oxygen (DO mg/L), and pH in the earthen pond of the broodstock cultivation and the rearing tank system for fish larvae were recorded daily with a DO meter. Water samples for nitrogen (NO2− mg/L) and ammoniac (NH3+) analyses were collected twice a month and kept cool in the refrigerator until they were analysed using the Hach Lange cuvette test method (DR2800 visual spectrophotometer, Hach Lange Gmbh, Germany).
2.9. Chemical Analysis
Samples of experimental test ingredients and diets were analyzed by using standard methods [
42]. Dry matter was determined by drying in an oven at 105
0C for 24 hours. Nitrogen (N) was determined by the Kjeldahl method and crude protein (CP) was calculated as N x 6.25. Crude fat (EE) content was analyzed using the Soxhlet method after acid hydrolysis of the sample. Ash content was determined by incineration in a muffle furnace at 550
0C for 12h. Amino acid profiles of ingredients and diets (
Table 2 and
Table 3) were analysed by high-performance liquid chromatography according to [
43]. The fatty acid composition of the diets (
Table 3) was determined using the total lipid extracts of the diets that were transesterfied with boron triflouride. Laboratory analysis of feed ingredients and diets was conducted at the Advanced Laboratory, Department of Science, Can Tho University, Vietnam.
2.10. Calculation
The following calculations were made:
Fertilization (%) = [Number of fertilized eggs / total number of eggs in the batch] × 100.
Hatching rate (%) = [Number of hatched eggs / total number of eggs in the batch] × 100.
Ripe eggs (%) = (Number of eggs with yolk position near one edge of the egg / total number of eggs counted) × 100.
Gonadosomatic index (GSI%) = (Gonad weight / total body weight) × 100.
Relative fecundity index (RFI) = (Total number of eggs in female ovary/Total weight of female).
Weight gain = Final body weight – Initial body weight.
Length gain = Final body length – Initial body length
Daily weight gain (DWG) = (Wf – Wi) / T), where Wf and Wi refer to the mean final weight and the mean initial weight, respectively, and T is the feeding trial period in days.
Specific growth rate (SGR%) = [(ln Wf – ln Wi) / T] × 100.
Food conversion ratio (FCR) = [total feed intake (g)/total wet weight
gain (g)].
Survival rate [(SR%) = (TFf / TFi) × 100], where the TFf is the total number of fish at the finish (harvest) and TFi is the total number of fish at the start.
2.11. Statistical Analysis
All data on induced spawning, egg fecundity, early lifestage development, hatching rate, growth performances of broodstock and larvae fish, survival rate of fry and fingerling, and water quality parameters were statistically analyzed by General Linear Model (ANOVA), using Pairwise Comparison and Tukey method for treatment comparisons (P ≤ 0.05 level of significance), MINITAB Statistic program (version 16).
4. Discussion
A diet rich in functional ingredients such as n-3 LC-PUFA fatty acids, essential amino acids, vitamin antioxidants, and prebiotic compounds has been shown to improve the broodstock, survival rate of larvae, yield, and farmed fish quality [
19,
44,
45,
46]. Colombo [
44] reported that maternal nutrition directly influence on the quality of the larvae and fingerlings. Lipids (fats and fatty acids) from fish oils, vegetable oils, microalgae and algal oils are an essential macronutrient for growth performances of fish and they provide at least three key essential fatty acids (EFA), which contain n-3 LC-PUFA, specifically DHA (22 : 6n-3) and EPA (20 : 5n-3). These substances are important for the metabolism of terrestrial animals and fish and contribute to their growth and physiological functions [
17,
18,
20,
47,
48]. Several researchers have shown that diets containing highly unsaturated fatty acids (HUFA), such as n-3 and n-6 HUFA influence gonadal development, eggs quality, fecundity, hatching and larvae survival rates [
15,
20,
49,
50,
51]. It is [
50,
52] reported that the dietary manipulation of n-3 and n-6 highly unsaturated fatty acid could improve levels and ratios of AA, EPA, and DHA , which were transferred to the resulting eggs with improvements in early survival and hatching success for European sea bass (
Dicentrarchus labra) and Channel catfish (
Ictalurus punctuates).
In recent years, the microalgal biomass market produces about 5,000 tonnes of dry matter per year and generates a turnover of approximately US
$ 136.25 million per year [
53,
54]. Ślusarczyk, Adamska [
17] reported that both fungi and algae are a potential source of natural antibiotics and antioxidants that would be safe to use and have no side effects. It is indicated that fungi and algae have the potential to replace fish meal and fish oil in aquaculture and ensure sustainability standards. Algae provide essential amino acids, valuable triglycerides such as lipids, vitamins, and pigments, making them suitable as nutritional supplements in livestock feed and aquafeed formulations [
17,
18,
19]. Several previous studies have reported that among the lipids in algae there are essential unsaturated fatty acids (EFAs) including arachidonic acid, eicosapentaenoic acid and the rare γ-linolenic acid (GLA) [
17,
48,
54].
Vitamins are organic compounds essential for supporting the normal growth and health of fish. They represent a significant cost in food fish and aquafeed production [
55]. Since fish often cannot synthesize vitamins and essential amino acids, they must be supplied in their diets [
15,
16,
55]. Vitamin premixes commonly used in food fish production diets are often considered adequate for farmed fish [
55]. Consequently, the relative importance of fatty acid and vitamin premix contents for reproductive performance and fish fry production can be qualitatively assessed by testing them as supplements in broodstock fish diets. The chemical composition, the content of essential amino acids and fatty acids of the experimental diets used in this experiment were comparable with the values reported for broodstock diets of European Sea Bass [
50], Gilthead sea bream [
16] and Channel catfish [
56]. Also the content of crude protein, crude fat and the composition of the vitamin premix compounds of the test diets in this study were in good agreement with feed given to adult channel catfish, tilapia, African catfish and striped catfish [
28,
39,
57].
Our results show that there were significant differences (P < 0.05) among the test diets in growth performance indices (final body weight, total weight gain, daily weight gain, specific growth rate) and reproduction indices (gonad somatic index, relative fecundity index, total number of eggs in the ovary, percentage of fertilized eggs, and hatching ratios) of the broodstock (
Table 4 and
Figure 2). The values for the diets in Treatment 5 were the highest, followed in descending order by Treatment 1, Treatment 6, Treatment 2, Treatment 3, and Treatment 4. This indicates that the Pangasius catfish broodstock received the diet nutrients well, without compromising growth and reproductive performance indices. [
15] and [
58] reported that gonadal development, fecundity and egg fertilization, egg size, and total egg volume all increased in some fish species when certain dietary proteins and essential nutrients, such as essential amino acids, vitamins, and fatty acids, were available in the feed..
The broodstock SGR in the present study was similar to values observed in a study on striped catfish breeders after six months feeding with a trial feed containing a 35% crude protein and a supplementary vitamin premix [
59,
60]. The GSI (%) and RFI (egg/kg) values in the present study were much higher than GIS (4.73–9.21%) and RFI (65,000–168,900 eggs/kg) previously reported for Pangasius catfish broodstock fed different dietary protein (25–45% CP) [
59,
61]. In general, the relative fecundity values (egg/kg) in this study were comparable to values (117,000–153,000 eggs/kg) of striped catfish broodstock spawners obtained by [
4,
59,
62]. However, it was much greater than value found for Basa (
Pangasius bocourti) and
Pangasius catfish broodstock reported by Cacot, Legendre [
63], Cacot [
64]. The fertilized egg incubation period in this experiment lasted for 33–36 hours to complete the hatching process and is similar to the hatching periods reported for Asian Pangasius catfish [
65]. The average hatching rate of eggs in the present study during the off? breeding season was approximate 78.5% (P < 0.05), which was in the range of the 70–80% hatching rates reported for
Pangasius sutchi during peak season in Bangladesh [
66] and Vietnam [
4,
5], Malaysia [
67] and Nepal [
62]. However, the hatching rate of the present study was much higher than the average values of 55–65% reported for Tra catfish (
Pangasius hypophthalmus) and Basa catfish (
Pangasius bocourti) in Vietnam [
63,
65,68] and 30% reported for yellowtail catfish (
Pangasius pangasius) in Bangladesh [68].
The survival rates of fingerlings reared for 45 days after hatching ranged between 22.0% and 66.3%. The highest final survival rate was recorded in Treatment 3 (66.3%), followed by Treatment 5 (45.3%), Treatment 6 (36.3%), Treatment 1 (23.3%), Treatment 4 (22.7%), and Treatment 2 (22.0%) (P<0.05). These results suggest that diets for Pangasius broodstock supplemented with 0.6% H-OVN, as well as those supplemented with 0.6% H-OVN mixed with 12.6% algal oil, can improve growth performance, reproduction of the broodstock, and survival rates of fingerlings. This improvement is likely due to the adequate provision of lipids, essential amino acids, and vitamins, which regulate metabolism and intestinal flora. The final survival rates (22.0–66.3%) of fingerlings in the present study during the over spawning season were 1.4 to 2.0 times higher than the survival rates (20–25%) during the main spawning season and (12–15%) during the over spawning season reported for Pangasius catfish by fish farmers in the Mekong Delta [
2,
4,
5,
6,
7].
Acknowledgments
The authors wish to thank DSM SINGAPORE INDUSTRIAL PTE. LTD, a company incorporated in Singapore for funding this research for a researcher team of Ton Duc Thang University, Vietnam to carry out this research. The authors wish to thank NAVICO Company, An Giang province for providing striped catfish broodstock and necessary facilities to conduct experiments and technician staff to support and assist the implementation of these experiments. On behalf of authors, I would like to thank Professor Torbjörn Lundh, Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Sweden for his valuable comments and advice on the feed nutrition for this research. Finally, we would also would like to thank the laboratory staff of the Advanced Laboratory, Department of Science, Can Tho University, Vietnam, and Mr. Tran Quang Dien and Mr. Qui, students of the Aquaculture Department, Faculty of Agriculture and Natural Resources, An Giang University, Dong Nai Technology University Vietnam, for their support and assistance during this study. Finally, the authors also thank professor Hakan Berg (Stockholm University, Sweden) and Dr. Charles Howie Former adviser in education to Faculty of Agriculture, An Giang University, and Agricultural Consultant for language revision of this paper.