This document summarizes several common bacterial diseases that affect fish and shellfish. It describes the causative agents, affected species, symptoms, diagnosis, and treatment/control methods for each disease. The major fish diseases discussed are furunculosis, columnaris, edwardsiellosis, vibriosis, pseudomonas septicemia, streptococcal infection, mycobacteriosis, and dropsy. The shellfish diseases summarized are filamentous bacterial disease and luminous bacterial disease.

1. BACTERIAL FISH AND SHELLFISH DISEASES
PREPARED BY: SADIYA FAROOQ
FACULTY OF FISHERIES
SKUAST-KASHMIR

2. BACTERIAL FISH DISEASES

3. Furunculosis
• Causative agent - Aeromonas salmonicida
• Furunculosis is highly contagious disease that affects fish of all ages.
• The infection causes high mortality in salmonids, though some other species of fish are affected.
• The name furunculosis is given because of its sub acute or chronic form, recognized by the presence of lesions resembling boils
i.e., furnuncles in the musculature.
• TRANSMISSION: Horizontal transmission occurs via the water column, but also through direct fish-to-fish contact and animal
vectors
• SYMPTOMS: Furuncles (or boils) involving skin and/or muscle progressing to lesions. Haemorrhages on the skin, mouth and
fin bases. Darkening of body colour and pale gills. Bloody discharge from nares and/or vent. 5) Stomach filled with mucus,
blood.
• DIAGNOSIS: Presumptive diagnosis is made by culture of a Gram-negative, oxidase positive, non-motile bacterial rod from
blood, kidney, or lesions on TSA or furunculosis agar with the production of a brown diffusible pigment. Some strains of
bacteria may not produce pigment. Diagnosis is confirmed by biochemical tests, slide agglutination and fluorescent antibody
tests specific for A. salmonicida.
• TREATMENT & CONTROL: It is done by removing the severely infected fishes from the pond and by supplying food containing
antibiotics like introfurans or sulphonamids etc. Disinfection may be done with 0.015 % sol. of merthiolate or 0.185 % sol. of
Acriflavin . 1% provindone-iodine sol. is most recommened ones owing to its relatively lesser toxicity compared to other
disinfectants. Iodine is used to decontaminate the surface of fertilised eggs to prevent vertical transmission (passage of
infection from parent to offspring).

4. Furunculosis in fish

5. Columnaris:
• Causative agent: Flavobacterium columnare.
• The commonly affected species include Ayu, tilapia, Common carp, channel catfish,
goldfish, rohu.
• SYMPTOMS: There is appearance of white spots on some part of the head, gills, fin
or body with a zone with a distinct reddish tinge usually surrounding this.
• On the gills, the lesions are more necrotic.
• On the skin, they develop into hemorrhagic ulcers.
• DIAGNOSIS: Columnaris disease can be presumptively diagnosed from disease
signs on the skin and gills of the host and from squash preparations made from
scrapings of the affected areas.
• TREATMENT & CONTROL: Maintain water quality. Separate diseased fish. Copper
sulfate dip at 40 mg/L for 20 min or 500 mg/L for 1 mi.

7. EDWARDSIELLOSIS
• Causative agent: Edwardsiella tarda.
• The commonly affected species include Tilapia, channel catfish, mullet, carp etc.
• SYMPTOMS: Edwardsiella tarda infection manifests itself by the presence of
small, 3-5 mm cutaneous or skin lesions located dorsolaterally on the body. The
skin loses pigmentation. A foul smelling gas is emitted when the skin is incised.
Internally, there is generalized hyperemia and enlargement of the liver and
kidney.
• E. tarda infection usually occurs during the warm, summer months.
• DIAGNOSIS: The bacterium is easily isolated from muscle and internal organs of
clinically diseased fish on most general-purpose media such as brain heart
infusion agar (BHIA) and tryptic soy agar (TSA).
• Small punctate colonies develop in 24-48 h on inoculated media.
• TREATMENT AND CONTROL: Improve water quality; Reduce stocking density;
Apply oxytetracycline at 55 mg/kg fish for 10 days.

8. EDWARDSIELLOSIS

9. VIBRIOSIS
• Causative agent: Vibrio alginolyticus, V. anguillarum and V. vulnificus.
• The commonly affected species include Grouper, rabbitfish, milkfish,
seabass, sea bream etc.
• Vibriosis usually occurs in the warm summer months, especially when the
stocking densities are high.
• SYMPTOMS: Large bright colour body lesions in the skin and muscles.
Gills may bleed with slightly pressure. Inflammation of intestinal tract.
Eye problems with cloudy eye, leading to pop- eye and finally eye loss.
• DIAGNOSIS: Isolation of the bacterium on agar plates (TSA or TCBS) and
identification either serologically or biochemically via tests.
• TREATMENT AND CONTROL: Dip treatment in copper sulphate sol. and
application of antibiotics with artificial food may be considered as curative
measures for vibrosis

10. VIBRIOSIS

11. PSEUDOMONAS SEPTICEMIA OR RED SPOT DISEASE
• Causative agent: Pseudomonas fluorescens, P. anguilliseptica, and P.
chlororaphis.
• The commonly affected species include Milkfish (Chanos chanos), goldfish
(Carassius auratus), tilapia (Oreochromis niloticus)
• SYMPTOMS: The disease causes small hemorrhages in the skin around
the mouth and opercula and along the ventral or abdominal surfaces. The
body surface may ooze blood and slime in severe cases but there is no
reddening of the fins and anus.
• Diagnosis: The organisms can usually be isolated from the kidney and
other internal organs of affected fish, as well as from the lesion. They grow
well on most common laboratory media such as BHIA, TSA and NA.
• TREATMENT AND CONTROL: Maintain proper stock management
procedures, ensure water quality and reduce stocking density. Transfer in
a tank and raise temperature to 26-27°C and maintain for about 2 weeks.

12. PSEUDOMONAS SEPTICEMIA OR RED SPOT DISEASE

13. STREPTOCOCCAL INFECTION
• Causative agent: Streptococcus sp.
• The commonly affected species include Seabass (Lates calcarifer), tilapia (Oreochromis
niloticus), rabbitfish (Siganus guttatus), ayu (Plecoglossus altivelis) etc.
• SYMPTOMS: The fish shows Erratic swimming, darkening of body color, unilateral or
bilateral exopthalmia, corneal opacity, hemorrhages on the opercula and the bases of the fins
and ulceration of body surface are the most common clinical signs.
• Diagnosis: The pathogen grows easily on tryptic soy agar supplemented with 0.5% glucose.
Colonies develop after 24-48 h of incubation at 20-30°C.
• TREATMENT AND CONTROL: Avoid overcrowding, overfeeding and unnecessary handling
or transport. Remove and slaughter promptly all moribund fish in ponds or net cages at
early stage of infection to prevent outbreak or reduce severity of disease. Apply erythromycin
at 25-50mg/kg body weight of fish for 4-7 days.

14. STREPTOCOCCAL INFECTION

15. MYCOBACTERIOSIS OR PISCINE TUBERCULOSIS
• Causative agent: Mycobacterium marinum, M. fortuitum and M. chelonae
• The commonly affected species include Siamese fighting fish (Betta splendens)
• SYMPTOMS: Listlessness, anorexia, emaciation, exopthalmia, skin discoloration and
external lesions ranging from scale loss to nodules, ulcers and fin necrosis are signs of
advancing infection.
• Diagnosis is usually based on the presence of granulomatous lesions, either grossly
visible or microscopic.
• CONTROL AND TREATMENT: Maintain water quality. Dip treatment for one minute in
1 : 2000 copper sulphate sol. for 3-4 days may be useful. Alternatively the fishes may be
destroyed and the pond sterized with KMnO4 or with soaked lime restocking .

16. MYCOBACTERIOSIS OR PISCINE TUBERCULOSIS

17. DROPSY
• Causative agent: Aeromonas hydrophila
• The commonly affected species include Catla catla, Labeo rohita and
Cirrhinus mrigala
• SYMPTOMS: In infected fish, there is accumulation of water in the body
cavity or in scale pockets thereby making the scale loose. The abdomen of
the fish gets distended. Mild ulceration may occur due to secondary
infection.
• DIAGNOSIS: It can be done by observing the abdomen of the fish which is
massively swollen and scales are pushed out by the swelling, causing a
pinecone-like appearance.
• TREATMENT & CONTROL: Removal and complete destruction of fishes ,
followed by draining , drying and disinfecting the fish pond with quicklime
is suggested to prevent spread of the disease. The infected fishes may be
cured by a two minutes dip in 5 mg / KMnO4 sol.

18. DROPSY

19. BACTERIAL SHELLFISH DISEASES:

20. FILAMENTOUS BACTERIAL DISEASE
• Causative agent: Leucothrix sp., Thiothrix sp., Flexibacter sp., Cytophaga sp.,
Flavobacterium sp.
• The commonly affected species include Penaeus monodon, P. merguiensis, P. indicus.
• SYMPTOMS: Infected eggs show a thick mat of filaments on the surface. In larvae and
postlarvae, normal respiration, feeding, locomotion, and molting may be seriously impaired,
resulting in slower growth rates. Frequent molting does not allow adequate time for the
bacteria to accumulate on the exoskeleton. Presence of fine, colorless, thread-like growth on
the body surface and gills as seen under a microscope
• DIAGNOSIS: Direct microscopic examination of wet mounts of larvae or postlarvae,
appendages and gill filaments excised from juvenile or adult shrimp, and of filamentous
organisms attached to external surfaces of the cuticle.
• TREATMENT AND CONTROL: Maintain good water quality with optimum dissolved oxygen
and low organic matter levels. Apply Cutrine Plus at 0.15 ppm copper in 24 h flowthrough
treatments. Apply 0.5 ppm copper in 4 to 6-h static treatments for PL 2 and older.

21. FILAMENTOUS BACTERIAL DISEASE

22. LUMINOUS BACTERIAL DISEASE
• Causative agent: Vibrio harveyi and V. splendidus
• The commonly affected species include Penaeus monodon, P. merguiensis, P.
indicus
• SYMPTOMS: Shrimps become weak and opaque-white. Affected shrimps often swim
to the pond surface and edges. Heavily infected shrimps in tanks and ponds show a
continuous greenish glow when observed in total darkness.
• DIAGNOSIS:The disease may be detected by bacteriological, histological,
serological, fluorescent antibody technique (FAT) and enzyme linked
immunosorbent assay (ELISA) using specific antibodies] methods.
• CONTROL AND TREATMENT: Disinfect incoming water and use filtration
equipment to prevent entry of luminous bacteria into the hatchery system. Use
immune prophylaxis or vaccination. Monitor bacterial population and diversity in
the intake and rearing waters of the shrimp pond. Apply antibiotics and other
antibacterial substances only as the last resort.

23. LUMINOUS BACTERIAL DISEASE

24. NON-LUMINOUS VIBRIOS
• Causative agent: Vibrio parahaemolyticus, V. alginolyticus, V.
anguillarum, V. vulnificus, V. damsela, V. fluvialis and V. penaeicida.
• The commonly affected species include Penaeus monodon, P. vannamei,
P. japonicas
• SYMPTOMS: Affected shrimp may show erratic or disoriented swimming
alternating with periods of lethargy. There is loss of appetite.
• DIAGNOSIS: Infection may be detected by bacteriological, serological,
slide agglutination, FAT and ELISA, and by Polymerase Chain Reaction
(PCR).
• TREATMENT AND CONTROL: Maintain good water quality and use
nutritionally adequate diets. Minimize handling and overcrowding; reduce
effects of other forms of stress.Perform immune prophylaxis or
vaccination. Apply antibiotics and antibacterial substances only as a last
resort.

25. NON-LUMINOUS VIBRIOS

26. • THANKYOU!