Modern shrimp culture industry developed rapidly in China since the late 1970s.The total yield of cultured shrimp had a significant increase during 1980s. However, there was about 70% reduction of shrimp production after 1993 due to ecological unbalance and disease occurred frequently. Traditionally, the prevention and the treatment of disease are based on the routine use of antibiotics that have non-targeted action against pathogenic bacteria, such inadequate use leading to resistant strains and ecological disturbance. Recently, the concept of biological disease control, particularly using microbiological modulator for disease prevention, has received widespread attention. A bacterial supplement of a single or mixed culture of selected nonpathogenic bacterial strains was termed probiotics. These live bacteria added to aquaculture systems to modify or manipulate the microbial communities in the water and sediment, to reduce or eliminate selected pathogenic species of microorganisms, to improve water quality by degrading waste, and generally to improve growth and survival of the targeted cultured aquatic species. However, the issue of using commercial bacterial flora to benefit aquaculture production systems is still controversial. To study the potential of ALKEN CLEAR-FLO 1200 in shrimp culture, some water qualitative parameters and bacterial number of the water samples taken from the tested ponds were investigated.
Materials and Methods
The commercial bacterial flora used in the tests was ALKEN CLEAR-FLO 1200, made by ALKEN MURRAY CORPORATION. It is a hazy liquid product with a slightly musty odor. This product is a combination of Bacillus subtilis, Pseudomonas aeruginosa, P. stutzeri, P. fluorescens, Escherichia hermanii (Manufacturer's note: B. licheniformis was always present, but was omitted from mention by the author of this study. Formulation changed in 1997: P.aeruginosa was deleted, Enterobacter cloacae was substituted for Escherichia hermanii, and P. stutzeri and P. fluorescens were reclassified as P. putida by ATCC) and two species of nitrifying bacteria Nitrosomonas and Nitrobacter. So ALKEN CLEAR-FLO 1200 contained bacteria 500 million cfu/ml has the function of organic matter degradation and ammonia removal.
Our study was carried out at Laizhou, Shandong Province, China from 19th Aug. to 30th Sept. 1999.The commercial bacterial supplement was added to the test pond (about 300 square meters) of the Japanese shrimp according to the manufacturers instructions. There was a control pond (about 200 square meters) which exchanged water daily while the test pond without water exchange during the test period. The juvenile shrimp obtained from a local farmer was added to each pond. The average body length and weight of the juvenile shrimp was about 7-8cm and 5-6g, respectively. Both shrimp ponds were managed with the same methods every day during the test period. The water samples were taken from both ponds weekly. The samples pH, temperature, salinity, chemical oxygen demand (COD), nitrite and ammonia were tested. Then the left water sample was added Tween 80 (5¼ g/ml) , mixed for 20-30 minutes thoroughly, serially diluted with sterile physiological saline and 0.1 ml from each dilution was plated onto ZoBells marine agar (2216E) and thiosulphate citrate bile sucrose agar ( TCBS) media. After 2 days of incubation at 28° C, the colonies were counted. At the end of the test, the mean body length and weight of the sampled shrimps were measured.
Results and Discussion
The effect on water quality: In our study, the effect of commercial bacterial flora on P. japonicus grown in the grow-out pond under no water exchange revealed no significant difference between the pond treated and untreated with ALKEN CLEAR-FLO 1200. But there was a noticeable difference in the level of ammonia between the treated and untreated ponds. As shown in data, it seemed that the commercial probiotics began to reduce the level of ammonia after one week. Even though the level of ammonia in the both ponds varied with time, the ammonia level in the experimental pond was much lower than that of the untreated pond from the second week to the end of the test. Thus, it appears that the probiotics addition affected the accumulation and removal rates of ammonia.
During the test, the level of COD and nitrite in the both ponds also varied with time. Moreover, they showed no major difference between both ponds. It appears that the commercial supplement had no effect on organic matter degradation and nitrite reduction. However, it is suggested that the low original level of COD and nitrite in the shrimp ponds and continual heavy rain during the test should be taken into account. Additionally, the used product in the test was on its way down in quality. (Manufacturer's note: Product shelf-life is 6 to 9 months, and product used in the test was 11 months old at the start of the test) It may be better to do more far studies on exploring the effect on the degradation of organic waste and nitrite removal.