Bacterial Diseases in fish culture Dr. Mohamed Sayed Marzouk Professor of Fish Diseases and Management, Fac. Vet. Med., Cairo University

Negative impacts of fish Diseases in Fish culture

During the breeding season: 1.Bad keeping quality. 2.Increased incidence of food poisoning (Microbial spoilage) 1.Low growth rate. 2.Bad Food conversion (FCR). 3.High fish mortality. After fish harvest:

Sources of infection and pollution in fish culture 1. Fish. 2. Drainage water. 3. Feeds (toxicated pellets, animal and poultry manure).

Surface drainage Water

Improper feeds

Clinical signs of Common diseases in fishes

Saddle back lesion in columnaris disease

Principals of increasing production and Disease control in fish farms

Bio-control and prevention of microbial infections 1.Raising the vitality of the fish (vaccination ???). 2. Destruction of the pathogenic micro-organism. 3. Prevention of the microbial attachment to the tissue receptors through: 1.Cell receptor blockage. 2.Unsuitable media (e.g. pH). 4. Stop or prevent bacterial multiplication.

Pathogenesis of infection: 1.Attachment of the organism to the cell receptors. 2. Rapid multiplication of the infectious organism with production of toxins or extracellular substances. 3. Invasion and destruction of the fish tissues with production of the clinical signs and lesions.

Principals of Bio-control in warm water fish culture Vaccination (of limited value) 1.Immuno-stimulants o ß- Glucan o Humic acid 2. Growth promoters o Digestive enzymes o Probiotics. o Prebiotics. Prevention of infection o Probiotics. o Prebiotics. o Symbiotics. Destruction of the MO. o Antibiotics. o Organic acids

Pathogenesis of infection: 1.Attachment of the organism to the cell receptors. 2. Rapid multiplication of the infectious organism with production of toxins or extracellular substances. 3. Invasion and destruction of the fish tissues with production of the clinical signs and lesions.

Antibiotics

Antibiotics attack and kill off bacteria without the mutation. The mutated ones survive after the antibiotics are gone. Reproduce, passing along the mutation to their offspring. More antibiotic-resistant bacteria than non-resistant.

Digestive enzymes

1.Cellulase 2.Xylanase 3.Protease 4.Phytase 5.Amylase 6.ß-glucanase 7.Pectinase Enzyme mixture 1.Amino Acids 2.Phosphorus 3.Calcium 4.Magnesium 5.Trace elements 6.Energy N.B. All these enzymes are natural products of living organisms (Aspergillus nigr).

Probiotics Living bacteria and yeast

One mode of action of a Probiotic

Prebiotics Non-living herbal and microbial extracts 1. Manna oligosaccharide(MOS) 2. Beta-glucan

MOS as a growth promoter in fish culture Decrease protein / trace elements complex Increase trace elements absorption Decrease intestinal pH through formation of short chain FAs. Absorption of minerals (Ca, Mg,..) in the form of FAs salts Stop growth of putrefaction and pathogenic bacteria Absorbed to form glycogen & CHO. in the liver Energy MOS fermentation in fish intestine

How MOS works

Un-healthy and destroyed intestinal villi from pelleted diet

High magnification of the destroyed intestinal villi from pelleted diet

High magnification of the healthy intestinal villi from pelleted diet with MOS

Improvement of fatty infiltration of Sea bream liver

Biological agents and fish immunity

1.Increase the quantity and quality of skin mucus. 2.Activate the phagocytosis process. 3.Indirect increase the antibody formation. Immune stimulants:

S. Cervisiae cell wall as immuno-stimulant in fish culture ß- glucan Activation of phagocytes cells and melanomacrophages in hempoietic organs through β-glucan receptor on the macrophage cell surface.

Activation of melano-macrophage centers in spleen of fed fish

Phagocytes from fish engulfing 1-2 yeast cells

Phagocyte from MOS fed-fish engulfing 6 yeast cells

Organic acids (Acidifiers) in fish culture

1.Short chain Fatty acids, namely Formic, Propionic and their salts (Sod. & Pot. diformate). 2.They produce their actions through regulation of the intestinal pH. 3.They are used to destroy the pathogenic bacteria in the fish intestine especially Vibrio spp. and Salmonella spp. 4.They increase the keeping quality of fish silage from spoilage bacteria. 5.They play an important role in Basa production. Acidifiers in fish culture:

Basa

Asian catfish (Pangasius hypophthalmus)

Rearing of Pangasius hypophthalmus fingerlings

Earthen ponds in Mekong Delta

Basa pink Fillet

Basa white fillet