International Journal of Aquaculture, 2017, Vol.7, No. 3, 15
-
22
16
Information on aquatic indigenous probiotics in Nigeria is scarce. Therefore, the aim of the present work was to
evaluate the effectiveness of antagonistic
Pseudomonas aeruginosa
previously isolated from healthy shrimp
intestine (Ariole and Aungwa, 2013) as biocontrol agent against
Vibrio
infection in shrimp (
Penaeus monodon
)
culture.
1 Results
1.1 Molecular identification
Molecular analysis conducted on
Pseudomonas
sp. Ps2 and
Vibrio
sp. V1 revealed that they are closely related to
Pseudomonas aeruginosa
strain XyC5 gi: 379070233 (Figure 1) and
Vibrio
mimicus
strain XQ gi: 648833882
(Figure 2) respectively.
Figure 1 Phylogenetic tree showing species relatedness of
isolate (Ps2)
Figure 2 Phylogenetic tree showing species relatedness of isolate
(V1)
1.2 Pathogenicity tests
The antagonistic
Pseudomonas aeruginosa
was safe to
Penaeus monodon
postlarvae when compared with the
control that showed mortality of 14% (Table 1). The shrimp became weak and sluggish after exposure to
Vibrio
mimicus
and finally, mortality of the shrimp was observed. Other clinical signs of black disease such as lethargy,
skin ulcers, swimming abnormality, and lack of appetite were very obvious. The thoracic appendage and
exoskeleton showed the presence of black nodules. The LC
50
of
Vibrio mimicus
for
Penaeus monodon
postlarvae
was estimated to be 3.2x10
4
cfu/ml. Mortality of 6% was recorded among shrimp in control group (Table 2).
Table 1 Safety test of
Pseudomonas aeruginosa
on shrimp (
Penaeus monodon
) postlarvae
Pseudomonas aeruginosa
(cfu/ml)
No of dead shrimp /No tested (with time intervals)
Mortality (%)
0 h
24 h
48 h
72 h
96 h
3 x 10
3
0/50
0/50
0/50
0/50
0/50
0%
3 x 10
4
0/50
0/50
0/50
0/50
0/50
0%
3 x 10
5
0/50
0/50
0/50
0/50
0/50
0%
3 x 10
6
0/50
0/50
0/50
0/50
0/50
0%
3 x 10
7
0/50
0/50
0/50
0/50
0/50
0%
Control (Non-infected)
0/50
2/50
4/50
5/50
7/50
14%
1.3 Histopathological test
There was no degeneration of the epithelial tissues and tubule lumen of the hepathopancreas (HP) of the shrimp
from control group (Figure 3) as well as shrimp from the group inoculated with
Pseudomonas aeruginosa
(Figure
4). However, the shrimp infected with
Vibrio mimicus
showed an abnormal hepatopancreas. The epithelial tissues
and the tubule lumen were degenerated. The nuclei were also disrupted (Figure 5).
