THESIS INFORMATION
Thesis title: Study on nitrifying bacteria in the sediment of intensive shrimp
pond (Penaeus monodon)
Specialization:
Marine/Brackishwater Aquaculture
Specialization Code: 62 62 70 05
PhD student:
Pham Thi Tuyet Ngan
Supervisors
Ass.Prof. Dr. Nguyen Huu Hiep, Can Tho University
Ass.Prof. Dr. Trương Quốc Phú, Can Tho University
Training University: Can Tho University
I.
THESIS SUMMARY
Nitrogen accumulation affects the quality and sustainability of many aquaculture
products. Using beneficial bacteria to reduce nitrogen accumulation has been widely used
for many decades. Thus, study of nitrifying bacterial population in intensive shrimp pond
sediments was conducted from 2008 to 2011. The research included (1) collection and
identification of bacteria isolated from intensive shrimp culture ponds sediments in Vinh
Chau, Soc Trang province by biochemical and molecular technique through the cycling
culture. (2) Determination of the water quality, the density of bacteria in the water and the
sediment during the cycling culture. (3) Assess the potential to improve water quality of
the isolated bacteria and their roles in the hatchery and grow-out shrimp in the laboratory
scale.
Nine strains of Bacillus, 8 strains of Nitrosomonas and 8 strains of Nitrobacter
were isolated. Based on physiological, biochemical tests and sequencing results 3 species
of Bacillus were determined: B. cereus, B. amyloliquefaciens and B. subtilis. One species
of Nitrosonomas (N. nitrosa) and one species of Nitrobacter (N. winogradskyi) were
determined. Most of the environmental parameters of sediment and bacteria in intensive
shrimp ponds were suitable for shrimp culture. Most of the isolated bacteria were positive
effect on water quality, decomposed organic mater, improved survival of shrimp and
increased shrimp growth.
II.
NEW FINDINGS OF THE THESIS
Several beneficial bacteria in shrimp ponds were isolated and selected for the
improvement of water quality in shrimp ponds. The results from laboratory conditions
showed that the appropriate bacterial density added in tank at larvae stage was 105
CFU/mL for Bacillus. This was the optimal density of bacteria on biodegradation of
organic matter and suppression of other bacteria, especially Vibrio and survival of larvae
was improved significantly. Most of the environmental parameters and sediment in
intensive shrimp ponds were suitable for shrimp culture.
Bacillus cereus was the dominant species in intensive shrimp ponds. This dominant
species was not present in Probiotics products (B. subtilis and B. licheniformis). This
finding proved that the bacteria species originated naturally in ponds rather than from
Probiotics products. Therefore this finding confirmed that bacteria used in probiotics could
not compete with native species, and they could only help to stabilize the density of
Bacillus, but could not change the indigenous bacterial population in the pond. So, when
Probiotics products were used in intensive shrimp ponds, most of the environmental
criteria were at permitted levels. Bacterial population decomposing organic mater was
stable during culture. Initial nitrifying bacteria was not appeared yet and after three weeks
of culture period its density increased. Dominant bacteria in the pond were not included in
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the species from biological products, but from the ponds. The predominant were the best in
water treating, in term of the longest present in the tank and increased survival rates as well
as the shrimp growth. So the isolated bacteria were beneficial bacteria and could be applied
in Probiotics products. The species B37 (B. cereus) was effective dominant species
compared to other isolated species. Finally, four species of bacteria B. subtilis (B41), B.
cereus (B38, B9) and B. amyloliquefaciens (B67) could be used to produce Probiotics.
III.
APPLIED FINDINGS AND FURTHER RESEARCH
3.1.
Applied findings of the thesis
The results from the thesis provided basic scientific data which could be applied in
producing safe and sustainable intensive shrimp culture in aquacultue. The new
findings from the thesis could be used to update aquaculture and environmental
microbiology lecture note as well.
3.2.
Further research
- Identification of other isolated bacteria and test of their capacity in treating water
of intensive shrimp ponds.
- Several field experiments should be carried out at different ecological
environments to determine the good effect of isolated beneficial bacteria in
intensive shrimp pond.
Supervisors
Ass.Prof. Dr. Nguyen Huu Hiep
Student
Ass.Prof. Dr. Truong Quoc Phu
Pham Thi Tuyet Ngan
CERTIFIED BY TRAINING INSTITUTION
RECTOR
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