Effects of Probiotic Dosage on Water Quality, Total Count of Aeromonas spp. and Pseudomonas spp. in Eel Anguilla bicolor Cultivation

This study was carried out to evaluate the effects of probiotic dosage on water quality, total number of Aeromonas spp. and Pseudomonas spp., in eel (Anguilla sp.) cultivation. Experiment was conducted by using fiber glass tanks (1x1 m) with 800 L water volume. Eel fingerling with 50 g average body weight were stocked at a density of 20 eel/tank in triplicates. Observation was conducted on total number of bacteria and water quality. The results indicated that the total bacterial count increased gradually by the time of cultivation with highest density of 1.49x10 cfu/mL. Probiotics at a dose of 40 mL/tank weekly increased the total count of bacterial cells in water. Probiotic application was able to decrease the total number of both Aeromonas spp. from 1.95 x 10 to 5.44 x 10 cfu/mL, and Pseudomonas spp. from 3.57 x 10 to 8.1 x 10 cfu/mL. Water quality during this study was not significantly affected by the application of probiotic. This result suggested that the application of proper dose probiotics suppresses Aeromonas spp. and Pseudomonas spp. cells density in water, and might decrease the bacterial infections in eel culture.


Introduction
Eel (Anguilla sp.) has economic value, high prices and very popular in Japan, Europe, America, Korea and Taiwan. In Indonesia, eel also is a popular food that the aquaculture still depends on the availability of eel seed (elver/glass eel) from capture [1]. Elver are available along the coast or estuary of the southern coast of Java Island, including Yogyakarta Special Region. Eel cultivation can be carried out starting from the supply of glass eel; larvae nursery with up to 2 g; grow out with up to 120-200 g for market size. The optimal water qualities of eel aquaculture in accordance with temperatures 28-33 o C [2]; dissolved oxygen (DO) 1-10 mg/L [3]; pH 6.5-8.0 [4]; and free CO2 < 25 mg/L are crucial in the eel culture.
Petrogrow is one of probiotic products is considered as a supplement contains with microorganisms which are given through various ways to balance the digestive microflora, so that it is beneficial for eel. Petrogrow also useful to support the environment by improving water quality and inhibits the growth of pathogens in water. Petrogrow is a liquid that contains beneficial microorganisms including Bacillus subtilis, Lactobacillus sp., Pantoea *Corresponding author: btriyatmo@ugm.ac.id sp., and Bacillus sp. The purpose of this research was to study the application of Petrogrow probiotics on water quality and the number of total bacteria of Aeromonas spp. and Pseudomonas spp.

Research Methods
The fiberglass tanks of 1x1 m 2 with water depth of 80 cm were used to culture eel with an average weight of 50 g. Each tank was equipped with continuous aeration. Eel fingerlings were stocked at a stocking density of 20 eel/tank, and cultured for 5 months. The experiment was designed in a completely random design in triplicates. The probiotic (PetroGrow, Petrokimia Kayaku) was applied at dosages of 0, 10, 50, 100 ml/m 3 water. The eel was fed with feed paste (39.8 % protein) at feeding rate of 3 % total body weight. Water change was carried out weekly by 35 % of total water volume. The total count of bacteria, Aeromonas spp. and Pseudomonas spp. were observed monthly by total plate count method on Tryptic Soy Agar (TSA) medium for total count of bacteria, and on GSP agar medium for total count of Aeromonas spp. and Pseudomonas spp. The water quality parameters observed including temperature, turbidity, pH, and dissolved O2 were measured with Water Quality Checker, while organic matter and free carbon dioxide (CO2 = ) were measured by titration method.

Result and Discussion
Total cells counts of Aeromonas spp. and Pseudomonas spp. subsequently are presented in Tables 1, 2, and 3. The total number of bacterial cells showed all bacteria including beneficial and pathogenic bacteria especially Aeromonas spp. and Pseudomonas spp.  Total Aeromonas spp. cell density in water added with doses of probiotic at 0, 8, 40, 80 mL probiotics/800 L every week were 194.7; 128.2; 69.2; 54.4 x 10 3 cfu/ml, respectively, while Pseudomonas spp. cells densities were 20.0; 8.1; 13.1 x 10 3 cfu/ml, respectively.. Probiotics at higher doses suppressed the growth of Aeromonas spp. and Pseudomonas spp. Water quality during experiment is presented in Table 4. The water quality is still favourable for eel culture.

Conclusions
The results of this study showed that: 1). Probiotics administration at doses up to 40 ml increases the total cell count of bacteria, specifically beneficial bacteria; 2) Addition of probiotics in water at higher doses suppresses the growth of Aeromonas spp. and Pseudomonas spp. 3). Addition of probiotics improve the water quality by reducing the organic matter and increasing DO.