ISSN: 1511-3701

Pertanika J. Trop. Agric. Sci. 34 (2): 195 - 206 (2011) © Universiti Putra Malaysia Press

Review Article

Streptococcosis in Tilapia (Oreochromis niloticus): A Review

Amal, M.N.A. and Zamri-Saad, M.*

Department of Veterinary Pathology and Microbiology,
Faculty of Veterinary Medicine, Universiti Putra Malaysia,
43400 UPM, Serdang, Selangor, Malaysia
*
E-mail: zamri@vet.upm.edu.my

ABSTRACT
Tilapia (Oreochromis niloticus) is a hardy, most cultured freshwater fish in the world. It has been contributing
to the world aquaculture since the ancient Egyptian days and remains a major freshwater fish species to be
cultured. Although tilapias are more resistant to unfavourable water quality than other freshwater fish, tilapias
have been reported to succumb to infection by Streptococcus, which was first observed among the populations
of rainbow trout (Oncorhynchus mykiss) farmed in the Shizouka Prefecture in Japan in April 1957. Since then,
the disease that is also known as ‘pop eye’ has been reported in many other fish species throughout the world,
contributing to an annual loss of approximately USD 150 million. Affected tilapia shows loss of appetite,
spine displacement, haemorrhages in the eye, corneal opacity, haemorrhages at the base of the fins and in the
opercula. The most prominent signs are uni- or bi-lateral exophthalmia (also known as “pop-eye”), distended
abdomen and erratic swimming. Control is mainly through implementing some preventive measure and
antibiotic therapy, while vaccination is generally not effective in preventing Streptococcus outbreaks in tilapias.

Keywords: Streptococcus, tilapia, infection

INTRODUCTION into many tropical, sub-tropical and temperate

The tilapias are freshwater fish that belong to regions of the world during the second half of
the family Cichlidae, and they are exclusively the 20th century.
associated with Africa and Middle East In the world where captured wild fisheries
(Trewaves, 1983). The Nile tilapia (Oreochromis are becoming increasingly depleted, tilapias
niloticus) is one of the first fish species to offer a possibility of commercialization because
be cultured in the world. Illustrations from of their superior culture adaptability. According
Egyptian tombs suggested that the Nile tilapias to FAO (2004), tilapias (Oreochromis sp.) are
had been cultured more than 4,000 years ago, i.e. among the most cultured fish worldwide. In fact,
about 1000 years before carp was introduced into the production of tilapias made the fish one of
China (Balarin & Hatton, 1979). Tilapias have the most important species for the 21st century
been called the “Saint Peter’s fish” in reference aquaculture (Fitzsimmons, 2000) which also
to biblical passages about the fish being fed to rose commercially in more than 100 countries
the multitudes (Popma & Masser, 1999). Pillay (Shelton & Popma, 2006).
(1990) reported that tilapias were introduced The estimated global tilapia production for
the year 2000 was 1.5 million metric tonnes

Corresponding Author
*
 Amal, M.N.A. and Zamri-Saad, M.

(MT) compared to merely 28,260 metric tonnes The aims of this paper are to review
in 1970. Similarly, the value of the farmed the current information on streptococcosis,
tilapias also increased from about USD 154 including epidemiology, main water quality that
million in 1984 to USD 1,800.7 million in 2002 contributes to the disease, mode of transmission,
(FAO, 2004). China alone produced 706,585 MT pathogenesis, as well as disease diagnosis, and
of farmed tilapia (representing 50% of the total control measures in farmed tilapias.
world production), followed by Egypt (167.7
MT), the Philippines (122.4 MT), Indonesia
STREPTOCOCCUS AND
(109.8 MT), Thailand (100.6 MT), Taiwan
STREPTOCOCCOSIS
(85.1 MT), Brazil (42 MT), Colombia (24 MT),
Malaysia (20.8 MT), and Laos (20.8 MT). The Streptococcosis is a disease that develops
farmed tilapias had exceeded 2 MMT in 2004 following the infection by Streptococcus sp.
worldwide (FAO, 2004; El-Sayed, 2006). They are spherical or ovoid in shape and 0.5-2.0
Tilapias have good characteristics for µm in diameter. They occur in pairs or chains
farming and are now so domesticated that when grown in liquid media, are non-motile,
this fish species has earned the title “aquatic non spore-forming and Gram-positive. A major
chicken”. Moreover, tilapias are fast-growing identification feature of Streptococcus is that it
with firm, white flesh, and able to survive in poor is Gram-positive that appears purple/blue when
water conditions, eat a wide range of food types, stained using a procedure called a Gram stain.
breed easily with no need for special hatchery On the contrary, most of the common disease-
technology (Nandlal & Pickering, 2004), as causing bacteria of fish are Gram-negative
well as feed at the base of the aquatic food web and appear pink with Gram stain (Yanong &
(Beveridge & Baird, 1998). Tilapias are tough Floyd, 2002). It is facultatively anaerobic,
and can tolerate a wide range of environmental requiring nutritionally rich media for growth
conditions; therefore, little environmental and commonly attacks red blood cell to produce
modification with low technology system is greenish discolouration (α-hemolysis) or
needed for culturing tilapias (Pullin & Lowe- complete clearing (β-hemolysis) on blood agar.
McConnell, 1982; Welcomme, 1988; Beveridge In addition, it is also a type of bacteria that are
& McAndrew, 1998; Nandlal & Pickering, fermentative in metabolism, producing mainly
2004). lactic acid, but without gas and catalase negative
Initially, tilapias were considered to be more (Holt et al., 1994).
resistant to bacterial, parasitic, fungal, and viral In fish, it was initially described among the
diseases compared to other species of cultured populations of rainbow trout (Oncorhynchus
fish. In more recent times, however, tilapias have mykiss) farmed in the Shizouka Prefecture in
been found to be susceptible to both bacterial and Japan in April 1957 (Hoshina et al., 1958).
parasitic diseases. Common tilapia pathogens After that, Robinson & Meyer (1966) reported
include Streptococcus sp., Flavobacterium two epizootics, both involving infections of
columnare, Aeromonas hydrophila, Edwarsiella golden shiner (Notemigonus crysoleucas) with
tarda, Ichthyophitirius multifillis, Tricodhina Streptococcus. Meanwhile, Plumb et al. (1974)
sp., and Gyrodactylus niloticus (Klesius et al., isolated Streptococcus sp. from over 50% of the
2008). It is important to note that streptococcal diseased fish during an epizootic in the estuarine
infections have become a major problem in bays along the Florida, Alabama, and the Gulf
tilapias farming and contributed to severe Coast of Mexico in the United States in 1972.
economic losses (Shoemaker & Klesius, In fish, Streptococcus spp. has been reported
1997). Streptococcus iniae and Streptococcus to cause considerable morbidity and mortality
agalactiae are the major bacterial species that worldwide. Estimated losses were around USD
affect the production of tilapias in the world 150 million annually in 2000 and these further
(Evan et al., 2006a). increased to USD 250 million annually in 2008
(Klesius et al., 2000; Klesius et al., 2008).
196 Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011
 Streptococcosis in Tilapia (Oreochromis niloticus): A Review

Streptococcus iniae was first isolated from a the preparation of S. iniae infected tilapias for
skin lesion of a captive Amazon River fish, Inia cooking (Lehane & Rawlin, 2000). S. agalactiae
geoffrensis (Pier & Madin, 1976). Since then, is the causative agent of neonatal meningitis,
the bacterium has been reported in many species sepsis and pneumonia in human (Baker, 1980).
of fresh, estuarine and marine fish species from It has been isolated from chickens, cattle, camels,
15 countries in 6 continents, including Africa, dogs, bottlenose dolphins, horses, emerald
Asia, Australia, Europe, as well as North and monitors, cats, fish, frogs, hamsters, humans,
South Africa. The susceptible fish include ayu mice, monkeys, and nutria (Wilkinson et al.,
(Kitao et al., 1981), barramundi (Bromage et 1973; Elliott et al., 1990; Evans et al., 2002;
al., 1999), coho salmon (Eldar et al., 1995a), Zappulli et al., 2005).
European seabass (Zlotkin et al., 1998), grey
mullet (Eldar et al., 1995a), grouper (Kvitt
Transmission
& Colorni, 2004), rainbow trout (Eldar et al.,
1994), red drum (Shen et al., 2005), snapper Many studies have been carried out to reveal the
(Ferguson et al., 2000), silver bream (Bromage transmissions of Streptococcus sp. According to
& Owen, 2002), tilapia (Klesius et al., 2006a), Nguyen et al. (2002), the newly introduced fish is
and yellowtail (Kaige et al., 1984). the most important factor that introduced S. iniae
Group B Streptococcus agalactiae, another and S. agalactiae into the farm. The bacteria are
emerging fish pathogen, has been shown to cause excreted in the faeces of infected fishes, survive
significant morbidity and mortality among a in the water and be infectious to other healthy
variety of freshwater and saltwater fish species fish (Nguyen et al., 2002). Besides, using the
throughout the world (Robinson & Meyer, infected thrashed fish as feed is believed to be
1966; Plumb et al., 1974; Evans et al., 2002). responsible for the outbreaks of streptococcosis
Streptococcus agalactiae was first reported in the among flounder in Korea (Kim et al., 2007).
captive freshwater shiners in 1966 (Robinson & Similarly, an experimental study revealed that
Meyer, 1966). Recently, this particular bacterium cohabitation of dead or infected fish with healthy
has been reported in fish from 7 countries in 3 fish resulted in the infection of the healthy fish.
continents, namely the United States (North Meanwhile, the horizontal transmission of the
America), Israel, Japan, Kuwait and Thailand pathogens between fish is believed to be the
(Asia), Honduras (Central America), and Brazil most common mechanism of dissemination.
(South America). This pathogen has also been A study by Xu et al. (2007) showed that the
isolated from 17 fish species including rainbow infection by this particular pathogen could occur
trout, seabream, tilapia, yellowtail, catfish sp., through wounds and abrasions of the skin. This
croaker, killfish, menhaden spp., mullet spp. and mechanism usually involved in fish that were
silver pomfret (Wilkinson et al., 1973; Plumb cultured in high densities. Furthermore, the
et al., 1974; Rasheed & Plumb, 1984; Elliot et transmission of Streptococcus between different
al., 1990; Baya et al., 1990; Eldar et al., 1995a; species of wild and cultured fish, within the
Vandamme et al., 1997; Evans et al., 2002; same aquatic environment, is likely to occur
Duremdez et al., 2004; Suanyuk et al., 2005; (Evans et al., 2002). This is because wild fish
Salvador et al., 2005; Evans et al., 2006a; Kim and fish cultured nearby have been found to be
et al., 2007; Garcia et al., 2008). infected with the same S. iniae strains in Israel
Streptococcus spp. is considered a diverse (Colorni et al., 2002). Similarly, Bromage &
group of bacteria that possess the capacity Owen (2002) reported that the fish cohabiting
to infect a wide range of hosts. Among barramundi pens had the same S. iniae strains
other, S. iniae has been isolated from humans as the barramundi. In addition, the transmission
with bacteraemia, cellulitis, meningitis, and among the species of reef fish has also been
osteomyelitis (Facklam et al., 2005). The source reported in the Caribbean (Ferguson et al., 2000).
of human infections has been associated with

Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011 197

 Amal, M.N.A. and Zamri-Saad, M.

Pathogenesis outbreak. Other factors usually come into play,

Infection by Streptococcus leads to various such that either the pathogen has an advantage
clinical signs, which include haemorrhages at the over the host or the immune system of the host
gill plate, loss of appetite, spine displacement, is compromised in some ways, increasing its
haemorrhages in the eye, corneal opacity, and susceptibility to the pathogen. This phenomenon
haemorrhages at the base of the fins and in the is often precipitated by “stress” (Yanong & Floyd,
opercula. The most prominent signs are uni- or 2002). Therefore, stress often plays a significant
bi-lateral exophthalmia, also known as “pop- role in the outbreaks of infectious disease in
eye”, and distended abdomen. The post-mortem fish populations. Some stressors that have been
examinations of the affected fish revealed the associated with the Streptococcal outbreaks
presence of blood-tinged fluid in the body include high and low water temperatures, high
cavity, enlarged and reddened spleen, pale but salinity and alkalinity (pH>8), low dissolved
enlarged liver, as well as inflammations around oxygen concentration, poor water quality (such
the heart and kidney. Meanwhile, hemorrhagic as high ammonia or nitrite concentrations), high
lesions were observed on the skin (Bullock, stocking densities, as well as harvesting and
1981; Yanong & Floyd, 2002; Salvador et al., handling effects (Chang & Plumb, 1996; Bunch
2005). Other clinical signs include darkening of & Bejereno, 1997; Bowser et al., 1998; Yanong
the skin and erratic swimming, which is either & Floyd, 2002).
spiralling or spinning just below the surface of Meanwhile, water quality parameters can
water. In some cases, however, the affected fish contribute to the development of disease. It
showed no obvious clinical signs before death is a well-known fact about the intolerance of
and the mortality is mainly due to septicaemia tilapias to low temperatures, which is a serious
and infection of the brain and nervous system constraint for commercial culture in temperate
(Barham et al., 1979; Yanong & Floyd, 2002). regions (Chervinski, 1982; Cnaani et al.,
Buchanan et al. (2005) identified enzyme 2000). Reproduction of tilapia is best in water
phosphoglucomutase as the virulence factor temperatures above 27℃, but it does not occur
for S. iniae. This enzyme inter-converts when water temperature is below 20℃. In sub-
glucose-6-phosphate and glucose-1-phosphate tropical regions with a cool season, the numbers
which play important role in the production of fry produced are decreased when daily water
of S. iniae polysaccharide capsules. Unlike temperature averages less than 24℃. It was
S. iniae, the regulatory proteins and enzymes concluded that the optimal water temperature
associated with cell surface metabolism have for the growth of tilapias is between 29℃ and
been revealed as the virulence factors for S. 31℃ (Popma & Masser, 1999), but a water
agalactiae. Therefore, the removal of the genes temperature of >31oC predisposes tilapias to the
that are involved in these functions can reduce outbreaks of Streptococcus agalactiae infection
the virulence. Fuller et al. (2002) found that (Evans et al., 2006a; Amal et al., 2008).
the virulence factor could also be caused by Oxygen is the first limiting factor for growth
the gene that is associated with β-hemolysis. and well-being of fish. Fish require oxygen for
However, additional research should be carried respiration, which physiologists express as the
out to identify and characterize the genes and the mg of oxygen consumed per kilogram of fish
virulence factors that regulate their expression. per hour (mgO2/kg/h). Although tilapia can
survive acute low DO concentrations of less than
0.3 mg/L for several hours, tilapia ponds should
FACTORS CONTRIBUTING be managed to maintain the DO concentrations
TO THE DEVELOPMENT OF above 1 mg/L. Metabolism, growth, and disease
STREPTOCOCCOSIS resistance are depressed when DO falls below this
The presence of the pathogen in the environment level for a prolonged period (Popma & Masser,
of the fish is inadequate to cause a disease 1999), predisposing tilapias to streptococcosis.

198 Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011

 Streptococcosis in Tilapia (Oreochromis niloticus): A Review

Moreover, it is a well-known fact that increasing In general, tilapias can survive in pH

water temperature will reduce the rate of DO ranging from 5 to 10, but they do best in a pH
in the water. The high water temperature also range of 6 to 9 (Popma & Masser, 1999). On
leads to increased respiration rate and oxygen the contrary, low water pH leads to behavioural
consumption by tilapias because of the high changes, damage of the gill epithelial cells,
metabolism rate. This further increases the reduction in the efficiency of the nitrogenous
demand for oxygen by tissues. Therefore, excretion and increased mortality. Wangead
dissolved oxygen concentration greater than 5 et al. (1998) reported that fingerlings and
ppm is required for a good growth of tilapias adult tilapias exposed to pH 2-3 showed rapid
(Swann, 1992; El-Sayed, 2006). swimming and opercula movement, surfacing
Other than water temperature and dissolved and gulping of air, as well as lack of body
oxygen, massive mortality of tilapia occurs position and mass mortality within 1-3 days. A
within a few days when fish are suddenly study by Chen et al. (2001), on the other hand,
transferred into water without ionized ammonia showed that tilapias exposed to high water pH
concentration greater than 2 mg/L. Meanwhile, for 7 days decreased ammonia excretion, but
a prolonged exposure for several weeks to un- increased urea nitrogen excretion. Bonga et
ionized ammonia concentration greater than al. (1987) revealed that slow acclimatization of
1 mg/L in water with low dissolved oxygen tilapias to low or high pH levels might enable
predisposes tilapias to diseases including the fish to withstand long-term exposures to the
streptococcosis. In fact, the prolonged exposures acidic or alkaline water. Thus, farmers should
to 0.2 mg/L of un-ionized ammonia concentration be aware of the sudden change in water pH to
are found to be detrimental to fish (Popma prevent stress on their cultured tilapias that may
& Masser, 1999). Ahmed et al. (1992) have lead to disease outbreaks (Bonga et al., 1987).
found that Nile tilapias exposed to ammonia
had lower number of red blood cells leading to
Diagnosis
haemolytic anaemia and significant reduction in
blood oxygen content, which enhances ammonia The presence of typical clinical signs and
toxicity. demonstration of Gram-positive cocci from
Nitrate is relatively non-toxic to tilapias. the brains, kidneys, eye or other internal
However, a prolonged exposure to elevated organs constitutes a presumptive diagnosis of
levels of nitrate may decrease the immune streptococcosis. The causative bacteria are best
response and induce mortality (Plumb, 1997). detected in the brains of diseased fish (Sugiyama
Inversely, nitrite is highly toxic to tilapias & Kusuda, 1981). Streptococcal infection
because it disturbs the physiological function should be highly suspected if the affected fish
of the fish and leads to growth retardation (El- exhibit abnormal swimming behaviour, pop-
Sayed, 2006). Nitrite may enter the bloodstream eye, haemorrhages, and rapid severe mortalities,
passively as nitrous acid and freely diffuses while Gram-positive cocci are found in brain,
across the gill membranes of the fish. After kidney, and/or other organs. A confirmed
entering the bloodstream, nitrite oxidizes diagnosis requires culture of internal organs,
the iron in the haemoglobin molecule from specifically the brain and kidney, followed by
ferrous state (Fe2+) to ferric state (Fe3+) and identification of the bacterium (Yanong & Floyd,
the resulting product is called methemoglobin. 2002).
Since methemoglobin is incapable of reversibly To recover the streptococci is apparently
binding with oxygen, exposures to nitrite can straightforward; bovine blood tryptose agar
cause considerable respiratory distress because (Naude, 1975; Roode, 1977; Boomker et al.,
of the loss in blood oxygen-carrying capacity 1979), brain heart infusion agar (BHIA) (Minami
(Boyd & Tucker, 1998). et al., 1979, Ugajin, 1981), Todd-Hewitt broth,

Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011 199

 Amal, M.N.A. and Zamri-Saad, M.

nutrient agar supplemented with rabbit blood 1998). Besides, a PCR technique using 16S-23S
(Kitao et al., 1981) are suitable media for ribosomal DNA intergenic spacers was found to
culture. Inoculated media should be incubated at be useful for the identification of S. agalactiae
22-37℃ for up to 48 hours before the “dull grey” from fish (Berridge et al., 2001). However, the
colonies of approximately 1-2 mm in diameter results of the PCR assay should be supported by
develop. This pathogen is easily grown on BHIA presumptive techniques to ensure the accuracy
(Plumb et al., 1974). Beside that, it also can of the detection.
grow on tryticase soy agar supplemented with Klesius et al. (2006a) developed an indirect
0.5% glucose, Todd-Hewitt broth agar (THBA), fluorescent antibody technique (IFAT) based on a
and horse blood agar (Kitao, 1982). highly specific monoclonal antibody for a rapid
A single colony from pure culture should detection of S. iniae. The olfactory epithelium
be Gram-positive cocci, oxidase, and catalase of naturally infected tilapias was demonstrated to
negative and either non-hemolytic or β-hemolytic be a reliable, sensitive and non-lethal sample site
on agar plate. The carbohydrate group antigen for the detection and identification of S. iniae.
test should be also among the first presumptive
test performed. The only group B streptococcal
Controls
species is S. agalactiae. In contrast, S. iniae
does not have a carbohydrate group antigen. Chemotherapy
If the streptococci hydrolyze starch, it is also Several drugs have been tested for the treatment
presumptive test for S. iniae (Evans et al., of streptococcosis. Among other, Darwish &
2004). Meanwhile, the biochemical and other Griffin (2002) found that oxytetracycline was
identification tests have been fully described effective in controlling S. iniae in blue tilapias
elsewhere (Shoemaker et al., 2001; Evans et (O. aureus). Oxytetracycline was incorporated
al., 2002). into the feed at 0, 25, 50, 75, and 100 mg/kg body
Rapid kits such as API 20E, API Rapid Strep weight. The 75 and 100 mg doses significantly
32, and API CH50 could not be used to identify increased the survival of the infected fish from
S. iniae because this particular bacterium is not 7% to 85 and 98%, respectively.
included in the database system. However, these Some reports concluded that erythromycin
rapid kits can be used for the identification of is effective against streptococcal infections
S. agalactiae and other Streptococcus spp. (Evans in cultured yellowtails (Shiomitsu et al.,
et al., 2006a). Jayarao et al. (1991) compared 1980) and rainbow trout (Kitao et al., 1979)
the identification systems between Vitek- at doses of 25-50 mg/kg/day for 4 to 7 days.
Gram positive and API Rapid Strep 32 system Doxycycline, oxytetracycline, kitasamycin,
and found that 93% of S. agalactiae isolates oleandomycin, josamycin, and lincomycin
could be identified using both the kit systems. have also been used to control streptococcosis
A comparison between API Rapid Strep 32 in the cultured yellowtail in Japan (Kitao et al.,
System and Biology system using Gram-positive 1979). Doxycycline, at 20 mg/kg/day for an
plates revealed that both the systems produced undetermined duration, has also been advocated
100% identification of the S. agalactiae isolates (Nakamura, 1982). Similarly, a novel fisheries
(Evans et al., 2006b). However, the Biology therapeutant, i.e. sodium nifurstyrenate, dosed
system using Gram-positive plates was able to at 50 mg/kg body weight of fish/day for three
correctly identify approximately 70% of S. iniae to five days has been proven to be successful in
(Roach et al., 2006). treating streptococcosis when incorporated with
Molecular diagnosis using the PCR feed (Kashiwagi et al., 1977).
technique is useful to identify streptococcus. Meanwhile, streptococcal infections respond
Many of the PCR techniques make use of the to antibiotic therapy, but the disease cannot be
16S rRNA gene as the molecular marker for legally controlled with antibiotics all the way to
the identification of S. iniae (Zlotkin et al., the market because the withdrawal period for all

200 Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011

 Streptococcosis in Tilapia (Oreochromis niloticus): A Review

effective antibiotics is longer than it takes for the Vaccines

streptococcal infection to return. Furthermore, A vaccine is a preventive tool used in a heath
it is only a matter of time before Streptococcus management strategy for controlling infectious
develops resistance to the antibiotics. In fact, disease (Klesius et al., 2006a). In aquaculture,
streptococcal strains at several facilities have the development and use of vaccines are now
already developed resistance to some antibiotics making rapid progress to achieve their full
(Darwish & Hobbs, 2005). Therefore, antibiotic potential as effective disease prevention tools.
treatment is generally ineffective and the need The objective of vaccination is to provide a
of proper vaccine has become a must (Klesius strong immune response to an administered
et al., 2000). antigen that is able to produce acquired long-
term protection against a pathogen. Killed and
Preventive measures modified live vaccines have been developed for
use in aquaculture. The type of immunity needed,
If causative streptococci are present in the mud
antibody or cell mediated, against a particular
and water throughout the aquatic environment,
pathogen are among the deciding factors in the
avoidance is not an easy or practical means of
development of a vaccine. Killed vaccines are
disease prevention. However, purchasing specific
usually administered by intraperitoneal (IP) or
pathogen-free stock, quarantining new arrival
intramuscular injection (IM) of individual fish.
fish stock, reducing overcrowding, avoiding
Injection is the least cost effective in terms of
overfeeding, keeping separate water supplies
labour and time. Meanwhile, killed vaccines are
for culture systems, minimizing unnecessary
considered safer than the modified live vaccines,
handling or transportation, removing dying
which may revert to virulence. Consequently,
and dead fish frequently, feeding pathogen free
future trends may include oral delivery of
ration, and keeping excellent sanitary conditions
vaccine, immersion delivery of killed vaccine,
will reduce the risks of disease outbreak (Inglis
development of additional modified live vaccines
et al., 1993; Klesius et al., 2008). Furthermore,
and multivalent vaccines and improved vaccine
periodic cleaning and disinfections of all the
adjuvants and immunostimulant. Vaccines
production units and equipment should be done
prevent disease and mortality, but they may not
to decrease the transmission of pathogens.
completely eliminate streptococci in surviving
Maintaining good water quality in the systems
fish (Klesius et al., 2008).
is also necessary (Klesius et al., 2008).
The first killed vaccine was developed to
Management control by ‘break-cycle’ has
prevent losses in trout due to S. iniae infection
been suggested (Amal et al., 2008). April-June
in Israel (Eldar et al., 1997). The mortality of
is a critical period in tilapia culture because
rainbow trout intraperitoneally (IP) immunized
of the high water temperature, while fish that
with formalin killed S. iniae vaccine was 5%,
weigh 150-300 gram are in critical condition.
whereas in non-immunized rainbow trout,
Huge and slow flow water bodies are critical
the mortality exceeded 50% in the field trial.
situations for development streptococcosis in
Whole cell and bacterial protein vaccines
Malaysia. Farmers are advised to manage the
were produced against S. agalactiae (Eldar et
cultured fish so that harvesting of adult fish of
al., 1995b). A non-autogenous killed S. iniae
more than 200 gram can be done before the
vaccine supplemented with its extracellular
coming critical period of April-June and to
products (ECP) was found to be effective in
ensure that only fish of less than 100 gram are
tilapia (Klesius et al., 1999). The mortality
available in the cage at the critical months of
was reduced by 91.3% in tilapia immunized IP
April-June. Nevertheless, farmers who still keep
with this vaccine at 30 days post-experimental
fish of 150-300 gram during the critical period of
challenge with S. iniae. The molecular weight
April-June are advised to reduce overcrowding
of the extracellular product was greater than
by re-distributing the fish in cages.
2kD. The relative percent survival was 95%

Pertanika J. Trop. Agric. Sci. Vol. 34 (2) 2011 201

 Amal, M.N.A. and Zamri-Saad, M.

in 25 gram tilapia and 84.2% to 94.7% in 100 Production Control in Anticipation of Global
gram tilapia. Besides that, western blot analysis Warming (pp. 48-51). Surabaya.
revealed predominant 54 and 55 kDa antigens in Baker, C.J. (1980). Group B streptococcal infection.
the extracellular products (ECP) of S. agalactiae Advances in Internal Medicine, 25, 475-501.
(Pasnik et al., 2005). The results of the study
Balarin, J.D., & Hatton, J.P. (1979). Tilapia: A guide
provided a correlation between protection and
to their biology and culture in Africa. Stirling,
antibody production against ECP and for the
UK.: University of Stirling.
importance of the 55 kDa antigen for vaccine
efficacy against S. agalactiae. Barham, W.T., Schoobee, H., & Smit, G.L. (1979). The
occurance of Aeromonas sp. and Streptococcus
spp. in rainbow trout (Salmo gairdneri). Journal
CONCLUSION of Fish Biology, 15, 457-460.
In conclusion, Streptococcus spp. (specifically S. Baya, A.M., Lupiani, B., Hetrick, F.M., Roberson, B.S.,
agalactiae and S. iniae) are very pathogenic as Lukacovic, R., May, E., & Poukish, C. (1990).
they can affect many fish species in the world. Association of Streptococcus sp. with fish
In particular, Streptococcosis has been reported mortalities in the Chespeake Bay and its
to occur in fresh, marine and brackish water fish; tributaries. Journal of Fish Diseases, 13, 251-
thus, it has caused millions economic losses of 253.
aquaculture in the world. Tilapias have become Berridge, B.R., Fuller, J.D., de Azavedo, J., Low,
a perfect host for Streptococcus infection. D.E., Bercovier, H., & Frelier, F. (2001).
Tilapia farmers should be advised and educated Development of a specific nested oligonucleotide
on a proper management of tilapias so as to PCR primer for S. iniae 16s-23s ribosomal
prevent the outbreak and spread of the disease. DNA intergenic spacer. Journal of Clinical
In addition, water quality parameter plays an Microbiology, 36, 2778-2781.
important role in tilapias farming. In more Beveridge, M.C.M., & Baird, D.J. (1998). Feeding
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