Quality
& Survival
Various concentrations of NS Series SPO were tested for growing 61-day old
and 100-day old prawns. Application of NS Series SPO at only 0.5 g/cu.m.
was equally effective as the higher concentrations of 1.0 and 1.5 g/cu.m.
Good water quality and high prawn survival were obtained with bacterial inoculations.
Research and development efforts are greatly needed to sustain the growth of the prawn industry in the Philippines. In 1987, prawn production showed a growth rate of 31% in volume (15,500 MT) valued at
PhP 3.2 Billion. Employment generated in this sector is tremendous considering that at least 20,000 hectares of brackish water ponds have been converted to prawn monoculture. However, the industry suffered a major setback due to the low market price of prawns. For these reasons, support and assistance in terms of industry-oriented researches on ways and means of improving production efficiency must be conducted at the soonest time possible.
One area of research and development is the use of specially selected and adapted strains of microorganisms inoculated in the ponds to improve water quality and survival rates of prawns. It is in this context that bioaugmentation of these bacterial strains in the new and innovative product, NS Series
SPO, were tested under semi- controlled conditions. Experimental results will provide baseline information for the eventual commercial application of NS Series in
prawn culture systems.
First Experiment
of prawn post-larvae, PL 18
MATERIALS
AND METHODS
Five thousand pieces of prawn post-larvae (PLI8) obtained from Calatagan, Batangas were transported to the experimental site in double plastic bags with oxygen. Young post larvae were stocked at 5,000 pcs/bag with 30 liters water during transport. Upon arrival, the transported post larvae were placed in 100-liter capacity tanks containing 20 liters of water with salinity of 23 ppt. The set-up was provided with moderate to vigorous aeration. They were then I conditioned to their new environment with '\ the gradual addition of 20 ppt sea water.
After two days, 50 pcs each of the post-larvae were stocked in 12 units of
100 liter capacity tanks containing 30 liters of water at 20 ppt. or an effective stocking density of 1,666.7 per square meter.
The required amount of NS Series spa was applied by preparing a stock solution of 1 gram of NS Series SPO in one liter of water. Aliquot amounts were added in each tank, i.e. 30 ml, 15 ml, and 9 ml each for treatment I, II and III. The un-inoculated lots served as control.
| Treatment |
Dosage |
|
g / cu.m. |
g / 30Liters |
| I |
1.0 |
0.030 |
| II |
0.5 |
0.015 |
| III |
0.3 |
0.009 |
| IV |
0 |
0 |
Prawn post-larvae were fed with SMI - President starter feed given at 3% of body weight (BW). The feed was prepared by mixing one part of feed to 5 parts of water
mixed and sieved through 80 microns plankton nets. Feed ration for the day was divided into 6 equal parts and fed to the prawns at every four-hour intervals.
The physio-chemical parameters of the rearing water were closely monitored. These I consisted of nitrite, nitrate, ammonia,
hydrogen sulfide, dissolved oxygen (D.O.), pH, total solids, and bacterial count. Samples were taken initially and every two days
thereafter using standard methods.
No water change was done for the entire duration of the experiment (20 days). Initial and final length and final survival of the test animals were recorded.
RESULTS
AND DISCUSSION
Nitrite and Nitrate levels
Nitrite and Nitrate levels of the The nitrite levels in the growing media of young
post-larvae, PL 18, were maintained
at very low levels in all treatments with bacterial inoculations (0.3, 0.5 and 1.0 g/cu.m.). Values obtained on the 20th day of culture period were below 0.2 ppm NO2 compared with the un-inoculated control which reached 0.592 ppm and 0.648 ppm on the 18th and 20th day of culture
respectively. These results demonstrate the effectiveness of NS Series SPO in reducing the nitrite level of water even at a very low concentration of 0.3 g/cu.m. for young
post-larvae. The same trend was observed in the nitrate level of the water (Fig. 1A and
1B).
Statistical analysis showed that bacterial inoculations of various levels provided a lot of beneficial effects and are
significantly different from the control without bacterial inoculations.
Ammonia content of the water
Bacterial inoculation was also very effective in maintaining the ammonia level of the rearing water of young prawn
post-larvae within optimum levels. This effect was most pronounced starting on the 12th day of culture when the un-inoculated control lots showed drastic increase in the ammonia level. However, the conditions are unlike in older prawns where the ammonia
accumulation in the control reached toxic levels of up to 3.2 ppm (see results of 2nd and 3rd experiments). With young PL 18, the highest value of NH 3,..N in the control without bacterial inoculation is only 0.316 ppm which is still within the optimum limits set for prawn.. This result can be explained by the fact that young post larvae are given less feeds compared with older prawns.
(Fig.1C)
Dissolved oxygen in the water
Mean dissolved oxygen levels of both control and treated lots were high during the experiment period. Values ranged from 6.28 to 7.02 ppm after 2 days of rearing. Dissolved oxygen (D.O.) readings were maintained within these high values up to 20 days
even without change of water and no photosynthesis occurring. The D.O. is well within the optimum limit for prawns which is set at a value higher than 3.5 ppm. The higher values of D.O. obtained in the control compared to the treated lots may be due to the consumption of oxygen by the bacteria during the decomposition of uneaten feeds and fecal matter excreted by the growing post-larvae.
The Duncan's Multiple Range Test showed that no significant difference was observed among the treated and controlled lots.
(Fig.1D)
pH of the water
The same trend was observed for both treated and controlled lots. Values started at pH 7.0 gradually becoming lower (pH 6.4 etc) as the experiment progressed. The range of pH for both control and treated lots up to the 16th day of culture without water change remained within the optimum limit set for prawn (ph 6.5 to pH 8.7).
Total Solids
The efficiency of bacterial inoculation was reflected in the total solids content of the medium. In the control lots, there was a build up of organic matter in the form of feces and uneaten feeds. With bacterial inoculation, degradation was going on efficiently in the system such that the total solid contents of the media remained low. This effect was most apparent starting on the 12th day of culture.
The total solids content of the rearing media were significantly lower in the inoculated lots compared to the control.
(Fig.1E)
Survival of post larvae
After 20 days, higher percent survival were obtained in all treatments inoculated with NS Series SPO compared with the control. The highest bacterial concentration applied (1.0 g/cu.m.), gave a high percent survival of 85.3% compared to the
un-inoculated control which was 54.3% only.
Duncan's Multiple Range Test showed significant difference between control and treated lots.
(fig.1F)
The bacterial population were significantly higher in the inoculated lots than the control. This effect was most apparent on the 14th day of culture. This may be explained by the fact that the inoculated bacteria multiplied in number because of the accumulation of organic matter in the rearing media. On the other hand, the non-specific, indigenous bacterial population in the control did not show significant increase in number.
| 
