Published: 2021-06-30

In vitro antibacterial activity of several plant extracts against fish bacterial pathogens

Tran Thi My Duyen, Nguyen Trong Tuan, Tran Thi Tuyet Hoa
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Crude methanol extract of 9 Vietnamese plants were in vitro screened for their antibacterial activity against three common freshwater fish pathogens including Aeromonas hydrophila, Edwardsiella ictaluri, and Streptococcus agalactiae. Agar disc diffusion method was used to evaluate the antibacterial activity, then solvent extract was performed for the extracts which exhibited the strongest and a broad-spectrum antibacterial activity. Minimal inhibitory concentration (MIC) was conducted for effective plant extracts using broth dilution method. The results indicated that most of the plant extracts exhibited antibacterial propeties to at least one tested bacterium. Headache tree (Premna corymbosa), bushwillows (Combretum quadrangulare) and Celandine spider flower (Cleome chelidonii) showed a broad-spectrum antibacterial activity. The largest inhibitory zones of 35 mm and 21 mm were observed  for the extract of Premna corymbosa against E. ictaluri and S. agalactiae, respectively. E. ictaluri was found to be the most susceptible for all of the extracts while A. hydrophila was the most resistant. The MIC of effective plant extracts against tested bacteria ranged between 0.39 mg/mL and 3.125 mg/mL. The result can be considered for further investigation of the development of an alternative therapy against bacterial infection in aquaculture.

Effects of rotifer densities on larval performance of spotted scat (Scatophagus argus)

Le Quoc Viet, Ly Van Khanh, Thi My Han Duong, Nguyen Duy Khoa Tran, Kotani Tomonari, Tran Ngoc Hai
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This study is aimed to determine the optimal rotifer feeding density for larviculture of spotted scat fish (Scatophagus argus). The experiment was randomly set up in triplicate with 5 treatments including 5, 10, 15, 20 and 25 rotifers/mL. The fish larvae with the initial body length and depth at 2,343 ± 110 µm and 812 ± 85µm, respectively, were stocked in 250-L tanks at 10 larva/L of density and 25‰ of salinity. After 21 days of rearing, the results showed that the larval growth were at 243 – 330 µm/day of DLG and 5.50 – 6.70 %/day of SGRL; 131 –204 µm/day of DDG and 7.20 – 8.93 %/day of SGRD, but no significant difference in larval growth performance was recorded among treatments (p>0.05). However, the highest survival rate of fish larvae (35.4-48.1%) was recorded in the treatments fed 5 and 10 rotifers/mL and was significantly higher than other treatments (p

The effect of guava (Psidium guajava) leaf extract on the quality of cobia (Rachycentron canadum) fillets during ice storage

Tran Minh Phu, Huynh Thi Kim Duyen, Le Anh Dao Nguyen, Nguyen Thi Nhu Ha, Nguyen Quoc Thinh, Tomoaki Hagiwara
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The aim of this study is to evaluate the effects of Psidium guajava leaves extract on the quality of cobia (Rachycentron canadum) fillets during in ice storage. A group of cobia fillets was soaked in Psidium guajava extract solutions at concentration of 0.03% (w/v) for 30 minutes while the other group soaked in cold ice water, considered as control treatment. The experimental fillets were packed and stored in ice for 15 days. Sampling were done on the 1st, 5th, 10th and 15th day. Analyzed parameters included temperature, total viable counts (TVC), sensory property, pH, moisture, water holding capacity (WHC), texture, total volatile base nitrogen (TVB–N), peroxide value (PV), Thiobarbituric acid reactive substances (TBARs), and fillet color. The results indicated that cobia fillets treated with guava extract solutions 0.03% showed significantly higher sensory property, lower PV and TBARs compared to the control treatment during ice storage. Based on the sensory property and total viable counts, cobia fillets can be used up to 10 days in both treatments remaining high quality of the cobia fillet.

Effects of salinity on growth performance, survival rate, digestive enzyme activities and physiological parameters of striped catfish (Pangasianodon hypophthalmus) at larval stage

Nguyen Thi Kim Ha, Nguyen Tinh Em, Nguyen Minh Ngoc, Yasuaki Takagi, Nguyen Thanh Phuong, Do Thi Thanh Huong
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The present study was to investigate the effects of different salinities (0 (control), 3, 6, 9, 12, 15‰) in striped catfish (Pangasianodon hypophthalmus) at larvae stage. Four-hundred individuals were randomly distributed to each 500-L composite tank (containing 250-L water) in triplicates. After 60 days, fish was sampled to determine survival rate, growth performance, hematological parameters, stress response indicators, and enzymatic activities. The results showed that the survival rate was highest in 6‰ (60.9%) and lowest in 15‰ (1.25%) (p

Drugs and chemicals use in frog farming in Dong Thap province

Nguyen Quoc Thinh, Tran Minh Phu
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The study was conducted to investigate the use of chemicals, drugs, and disease occurrence from frog farming in Dong Thap province. Data were collected through a questionnaire from a random sample of 30 frog farmers from January to April 2020. The results showed that the common diseases were pus in liver (66.7%), hemorrhage (66.7%), and digestive tract problems (flatulence, abdominal intestine, 40%). Farmers used antibiotics to treat diseases and chemicals to treat parasitic infection without knowledge on pathogens. Commonly used antibiotics were oxytetracycline (53.3%), doxycycline (63.3%), amoxicillin (53.3%), florfenicol (36.7%), and sulfamethoxazole/trimethoprim (46.7%). In addition, other antibiotics such as tetracycline, enrofloxacin, ciprofloxacin, rifampicin were used in some households. Farmers used iodine (26.7%), copper sulfate (20%), and BKC (16.7%) as disinfectants. There was no antibiotic residues test prior to sell to traders. It is necessary to support farmers in knowledge on diseases, drugs/chemicals use, and safety in the use of drugs and chemicals.

Effects of temperature on growth performance, survival rate, digestive enzyme activities and physiological parameters of striped snakehead (Channa striata) at fry stage

Do Thi Thanh Huong, Nguyen Thi Kim Ha, Nguyen Tinh Em, Tang Minh Ky, Yasuaki Takagi, Nguyen Thanh Phuong
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The effects of temperature on growth performance, survival rate, digestive enzymatic activities, and physiological responses of striped snakehead (Channa striata) at fry stage were evaluated. The study consisted of two trials including (1) determination of temperature threshold and (2) effects of different temperatures (24°C, 27°C (control), 30°C, 33°C and 36°C) on growth performance, survival rate, digestive enzyme activities and physiological parameters of striped snakehead fry stage for 90 days. The growth experiment was conducted in 500-L tank (250-L water) with triplicates. The stocking density was 300 individuals per tank. Striped snakehead at fry stage showed a high tolerance to temperature ranging from 10 to 40ºC. After 90 days, fish reared in 30°C performed the greatest weight and survival rate (13.1±3.12 g/fish and 15.5±4.63%, respectively). The number of red blood cells and hemoglobin concentrations increased with the increase in temperature. It was discovered that different temperatures (from 27 to 36°C) did not significantly influence the number of white blood cells, osmolality, and ion concentration of fish. Glucose and cortisol concentrations increased with temperature rises and peaked in fish reared at 36°C, while temperatures of 30oC and 33oC showed higher digestive enzyme activities. It proves that 30°C is the optimal level for striped snakehead fry rearing.

Screening utilization of different natural prebiotic extracts by probiotic Lactobacillus sp. for development of synbiotic for aquaculture uses

Huynh Truong Giang, Hung Hai Vu, Thi Cam Tu Phan, Pham Thi Tuyet Ngan, Vu Ngoc Ut
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The study is aimed to develop a relevant synbiotic to promote growth performance of the whiteleg shrimp, Litopenaeus vannamei. For this, four common natural fiber extracts from Arcera banana, Siamese banana, yellow sweet potato, and white sweet potato were screened for supporting the growth of Lactobacillus sp. which was isolated from whiteleg shrimp intestines with probiotic activity, prebiotic score, and ability to induce bacterial enzyme activities of protease, leu-aminopeptidase, and a-amylase. Results showed that Lactobacillus sp. was able to utilize all extracts from banana and sweet potato as the sole carbon sources. At 24 hours of culture, the growth of Lactobacillus sp. was highest after adding the extract from white sweet potato as the sole carbon source. Considering pathogenic bacteria, including Vibrio parahaemolyticus, white sweet potato extract had the highest prebiotic score with a mean of 0.25 as compared with those of V. harveyi with a mean of 0.16. White sweet potato extract induced the highest activities of protease. These results indicated that white sweet potato extract was more suitable for combining with Lactobacillus sp. as a synbiotic for shrimp culture.

Effects of stocking density on performance of snubnose pompano juvenile (Trachinotus blochii) reared in recirculating system

Tran Ngoc Hai, Nguyen Duy Khoa Tran, Kotani Tomonari, Ly Van Khanh, Le Quoc Viet
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This study aimed to determine appropriate densities for rearing pompano juvenile (Trachinotus blochii) in a recirculating system. Four treatments of stocking density were evaluated including 500, 1.000, 1.500, and 2.000 inds/m3 in triplicate. The experimental system for pompano rearing was designed with 120-L tanks connected to 1 settling tank, 1 filter tank, 1 stone filter tank (contained 250 L of filter volume for each tank). The system was fulfilled with marine water at 30 ‰ of salinity and aerated continuously. Pompano were initially stocked at 0.07 ± 0.03 g/fish of body weight and daily fed using commercial pellet contained 55% of crude protein. After 30 days of rearing, the fish stocked at 1.000 individuals/m3 showed the best results in growth rate (0.060 g/day of DWG and 10.97 %/day of SGR) and was significantly higher than the treatment stocked at 1,500 and 2,000 inds/m3 (p < 0.05), however, no significant difference was observed between  1,000 and 500 treatments (p > 0.05).

Intraspecific variations in morphology of swamp barb (Puntius brevis)

Le Ngoc Son, Duong Thuy Yen
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Understanding inter-population variation and sexual differences in morphology is a fundamental part of taxonomic and biological research. External morphology of swamp barb (Puntius brevis) was compared between sexes and among three populations in the Mekong Delta, including O Mon-Can Tho (n=86), U Minh Thuong-Kien Giang (n=49) and U Minh Ha-Ca Mau (n=77). The results illustrate that color and countable parameters are similar in all populations. Nonetheless, 9 out of 20 morphometric indices are significantly different among three populations (P

Incorporation of amine functional group on surface of hydroxyapatite prepared fromstriped catfish (Pagasianodon hypophthalmus) bone

Ho Quoc Phong, Yasuaki Takagi, Huynh Lien Huong, Nguyen Thanh Tuyen, Tran Minh Phu, Le Thi Minh Thuy, Cao Luu Ngoc Hanh
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This study was conducted to incorporate amine functional groups on the surface of hydroxyapatite to enhance its potential application in biomedical materials. Hydroxyapatite particles (HA) were synthesized from striped catfish (Pagasianodon hypophthalmus) bone and surface modified by grafting with (3-aminopropyl)triethoxysilane (APTES). Important factors affected grafting efficiency such as concentration of APTES, water content, reaction temperature and reaction time were studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) were used to confirm the grafting reaction on HA surfaces. Grafting efficiency was evaluated based on intensity of characteristic absorption peaks of APTES. The experimental results showed that amine functional groups were successfully introduced on HA surface at optimal condition of 0.2 M APTES, 0.75 wt.% water content, at 60°C and 12-hour reaction time.

Characterizations of sulfur oxidizing bacteria from extensive shrimp ponds

Huynh Truong Giang, Hung Hai Vu, Thi Cam Tu Phan, Pham Thi Tuyet Ngan, Vu Ngoc Ut
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The aim of this study is to characterize the sulfur oxidizing bacteria (SOB) isolates from the sediments of extensive shrimp ponds for recommending the use of this group for water quality management in aquaculture. Sediment samples were collected from 12 extensive shrimp ponds located in Tra Vinh, Soc Trang, Bac Lieu, and Ca Mau provinces. To screen the potential sulfur oxidizing bacteria, medium was amended with sodium thiosulfate, and the sulfate ion production ability and sulfur oxidase enzyme activity of the isolates were measured spectrophotometrically. Results showed that 30 isolates grew on the thiosulfate agar medium. Among these, only five isolates reduced the pH of the growth medium and showed high sulfur oxidase activity and production of sulfate ion when isolates were inoculated with thiosulfate as a substrate. Physiological and biochemical tests indicated that five selected isolates were Gram negative, short rod, non-motile, non-spore forming, negative for oxidase reaction, and positive for catalase reaction. The isolates SOBTB1.1 and SOBTB6.2 showed the significantly higher sulfur oxidase activity and production of sulfate ion compared to other isolates. SOBTB6.2 isolate produced sulfate ion and exhibited higher sulfur oxidase activity at pH4-5, followed by pH6-7. It is, therefore, suggested that the SOBTB 1.1 and SOBTB6.2 could be promising sulfur oxidizers for further research and uses in aquaculture.

Investigation of parasites in the digestive tract of white leg shrimp (Litopenaeus vannamei) cultured at coastal farms in the Mekong Delta

Dang Thi Hoang Oanh, Nguyen Thi Nhu Thuy, Vu Ngoc Ut
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A total of 291 white leg shrimp samples were collected from 70 cultured ponds in Soc Trang, Bac Lieu and Ca Mau provinces in the Mekong Delta and subjected to endoparasitic detection in the digestive tract. Collected shrimps displayed unhealthy behaviors such as stop or less feeding and lethagic swimming. Pathological signs in the gastrointestinal tract include (1) empty midgut and stomach together with pale and atrophy hepatopancreas; (2) empty, little or discontinued food in the midgut; (3) slow growth and variation in sizes; and (4) white feces. The results from fresh and Giemsa stained smears methods revealed that 96.5% of sampled shrimps were infected by gregarine parasite at different developmental stages. A prevalence infection of 24.7% was recorded with Vermiform present in the hepatopancreas by fresh smear and histology. Histopathological analysis noted that 7.9% of collected shrimp samples had Enterocytozoon hepatopenaei (EHP) spores in hepatopancreas and midgut and confirmed by PCR analysis.

Survey on the roles and impacts of seaweeds and aquatic plants in the improved extensive black tiger shrimp farms in Bac Lieu province

Nguyen Thi Ngoc Anh, Nguyen Hoang Vinh, Lam My Lan, Tran Ngoc Hai
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A survey was conducted to assess the roles and impacts of seaweeds and aquatic plants on the production and financial efficiency of black tiger shrimp in improved extensive farms through direct interviews with 60 farmers from Dong Hai district, Bac Lieu province. The householders were divided into two groups based on the presence of natural seaweed and aquatic plant, including group 1: the presence of different seaweeds and aquatic plants but the absence of red seaweed (mixed vegetation) and group 2: the presence of red seaweed dominates over the mixed vegetation. The surveyed results showed that group 2 had an average shrimp yield of 268.6 kg/ha/year with a profit of 58.4 million VND/ha/year, which was higher than that of group 1 (shrimp yield of 203.1 kg/ha/year and profit of 43.0 million VND/ha/year). Almost all farmers agreed that seaweeds and aquatic plants acted as important roles in improving water quality, providing natural food and shelter for shrimp, crab, and fish. Farmers, on the other hand, claimed that their excessive growth (high biomass) increased water transparency, limited living space, and hampered the activities of shrimp, crab, and other organisms, as well as reduced shrimp growth and production and polluted water after seaweed died off. Notably, the farm that maintained vegetation coverage ≤50% obtained higher shrimp production and profit than pond with coverage >50%. Moreover, 46.7% of farmers preferred red seaweed over other seaweed and aquatic plant species in their farms.