Summary:
An undergraduate honors paper
The skin is a barrier against infection.
- outer layer (epidermis)
- covers the scales
- secretes mucus (that helps prevent invaders from getting to the skin)
- usual site for infections
- middle layer (dermis)
- scales grow out of the dermis
- contains color pigments
- inner layer (subcutis or hypodermis)
- lots of blood vessles
- connective tissue
Signs of bacterial dermatitis (bacterial skin infection) are
- reddened lesions, sores, or ulcers on the body;
- reddening of the base of the fins; and
- dulling or darkening of skin color
Other nonspecific symptoms may include
- anorexia (loss of appetite),
- weight loss, and
- decreased activity.
Gram-negative bacteria:
Most bacteria commonly isolated from fish are Gram-negative bacilli. May be rapidly fatal.
Aeromonas salmonicida
- skin nodules (furunculosis) and ulcers
- secondary septicemia is common
Aeromonas hydrophila
- always present in the water
- symptoms similar to A salmonicida
- hemorrhagic septicemia
Flavobacterium columnare (previously known as Flexibacter columnaris)
- always present in the water
- gill erosion
- skin lesions starting as shallow, white erosions and progressing to yellowish-brown ulcers
- typically found on dorsal area
Pseudomonas fluorescens
- lesions similar to Aeromonas
Edwardsiella sp. (tarda and ictaluri)
- initially - small ulcers and hemorrhages in the skin and muscles or pinpoint skin hemorrhages
- later - large abscesses with stinky, gas-filled cavities in muscles
- lesions similar to Aeromonas
Gram-positive Bacteria
Rods
Nocardia
- raised masses in mouth, gills, and skin which eventually ulcerate
- granulomas in organs
Aerobic, bacilli
Mycobacterium (fortuitum and marinum)
- wasting away
- granulomas in many tissues and organs, including the skin
- Treatment is largely ineffective.
- can be transmitted to humans
Diagnosis:
- Culture and sensitivity testing
- Stains can help figure out which is which
Treatment
- isolate in hospital tank
- antibiotics,
- salting tank to 0.3%
- 8% salt dip
- cleaning the wounds with iodine
- good water quality (partial water changes/tank maintenence/don't overstock)
- good diet
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