"what's on my fish" ?

What Is Bacteria?

Bacteria come in various shapes and sizes, but all are microscopic single-celled organisms that can not be seen with the naked eye the cell contains a simple strand of genetic material that lies free within the cell.

In addition to the strand-like genome, there are also small additional bits of Genetic material known as plasmids, which reproduce separately from the main chromosome and are readily transferred between bacteria to develop resistance to drugs such as antibiotics. Bacteria can reproduce by cell division,

which means the numbers within a bacterial colony can multiply very quickly reproducing to millions in just a few 

hours. But they can also reproduce
sexually. Transferring genetic material in the plasmids enables bacterial
resistance to antibiotics to spread quickly. Bacteria are naturally present in the pond.

The biological filtrations are reliant on the beneficial nitrifying species to oxidise ammonia (NH4/NH3) Into nitrate (No3). In addition to the nitrifying species, many hundreds of free-living species of bacteria are

found in the pond and live in harmony with your fish. A fishes gut harbours its bacterial flora and these not only help the fish to digest food but even assist in fighting off bacterial species that have the potential to cause disease in most instances, stressed fish are most susceptible to bacterial infections but true bacterial disease in most instances can only be caused through the introduction of an infected or carrier host.

Fish are more likely to become infected with bacteria such as Aeromonas hydrophila.

This ubiquitous species is found in every aquatic
environment, but is an opportunist pathogen, taking advantage of weak or stressed fish particularly if there is damage to the epidermis, once this outer layer of skin has been damaged bacteria quickly colonize the wound,

Which can lead to ulceration indicating that the fish are stressed and this has allowed bacteria to infect any slight wound. You must be quick to give the fish the appropriate cause of medication.

Ulcer/ Bacterial Disease

An outbreak of ulcer disease in a pond may be due to infection with several different species of bacteria.

Most Commonly, the primary agent in an Outbreak of ulcers is atypical Aeromonas salmonicida, a species of bacteria that is a true fish pathogen,
infecting the skin and initiating an ulcer. Once the skin has been breached by the atypical A. salmonicida.

The lesion is rapidly colonized by Aeromonas hydrophila, a related but ubiquitous species found in every aquatic environment. In most instances, laboratory results from swabs taken from an ulcer or lesion reveal only A. hydrophila as A. salmonicida is difficult to isolate.

Flavobacterium columnare may also prove to be a problem for the fish keeper leading to fin-rot & ulcers. Whichever species of the bacterium is suspected, it is important to try to have the infection identified to ascertain an appropriate course of medication and plan of treatment.


Signs of infection with bacterial disease are variable.

Often, there may be an initial display of irritability, with twitching fins or repeated rubbing or flicking, but samples of mucus fail to show any parasite infection.

The more obvious signs are lethargy when the fish is very inactive, accompanied by loss of appetite.

If the fish is stressed or in any way debilitated, once its skin has been damaged either by physical damage, other pathogenic bacteria or even viral infection, it will quickly be infected.

Early signs of infection are localized areas of inflammation, reddening and sometimes areas of raised scales.

All too often fish keepers only become aware of bacterial infections when there are already signs of having ulcers or open wounds.