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• Now through the end of August, one of our favorite flakes, Meat Eaters Flake, is 20% off!  Click here! (this is the only link that works for the lower price) You can also add it directly to your supply  shopping cart with this button.

  8 oz Meat Eaters Flake $4.00 1 lb Meat Eaters Flake $6.80 5 lb Meat Eaters Flake $28.60

Disease Prevention Series

An Introduction to Bacteria

A bacterium (bacteria, pl.) is a single prokaryotic cell and so, by definition, lacks a nucleus and is, generally, much smaller than any eukaryotic cell.

Bacterial cells come in a variety of shapes and sizes. The shapes most relevant in terms of fish health are coccus (spherical) and rod. The smallest bacterial cells are 0.2µm in diameter and are usually no larger than 50µm in diameter. However, a very unusual marine bacterium is the largest known prokaryote, and has a diameter of 0.75mm (or 750 µm). This cell can actually be seen with the naked eye!

Another important distinction between bacterial cells is their variable tolerance to oxygen. Bacterial cells will fall into one of the following groups:

• Aerobes: grow in the presence of the normal oxygen level of air (21% O2).
• Microaerophiles: are aerobes that grow best in oxygenated environments with lower concentrations than that of air.
• Facultative aerobes: will use oxygen if it is present, but can also grow in anoxic conditions
• Anaerobes: do not use oxygen.
  • Aerotolerant anaerobes: tolerate the presence of oxygen, but are unable to use it.
  • Obligate anaerobes: experience either inhibition of growth or death as a result of the presence of oxygen.

It is very common to classify most pathogenic bacteria based on their gram-staining characteristics. The Gram Stain is classified as a differential stain because cells will stain different colors based on certain morphological characteristics. When performing the gram stain, gram-positive cells will stain purple and gram-negative cells will stain pink/red due to differences in the structure of their cell walls. Any purple cells have retained the dyes crystal violet and iodine, while pink/red cells have retained the dye safranin. The majority of bacteria which are pathogenic to tropical aquarium fish are gram-negative. Click here to read about how the gram stain works.

You Could Be This Month's Winner! As a newsletter subscriber you are automatically entered in our August drawing for a $75.00 coupon good on any fish order. The drawing will be held at the end of August. Absolutely no purchase necessary--just sit back, relax, and you could win free fish! Winner is not obligated to receive the free gift. *Winner pays shipping cost. *Winner is not obligated to spend the entire $75. Don't want or have room for $75 worth of fish? There is no minimum order, just keep in mind that the coupon is one-time use only. It won't carry a balance if you don't spend it all. *Coupon is good for 90 days from the date issued. *You can only win once in any 12 month period. * And The Winner Is... Sue Herfel is the winner of our July drawing for a $75.00 voucher from our Fish Store. You could be this month's winner!

Good, Bad, or Both?

As any mildly experienced aquarist knows, not all bacteria are bad news. Even though all pathogenic prokaryotes are bacteria, not all bacteria are pathogenic. In fact, the benign, nitrifying bacteria that colonize filter media (and all other hard surfaces in an aquarium) do a great service by breaking down the ammonia waste produced by fish. The Nitrogen Cycle is further explained in our Encyclopedic-Dictionary.

Bacteria which are classified as primary pathogens will cause disease in otherwise healthy fish. In the case of such detrimental bacteria, prevention is the key to avoiding potentially massive problems.

There is also a group of bacteria which fall into the gray area of opportunistic pathogens. Opportunistic bacteria are considered a part of the normal flora and will not cause problems with healthy fish. However, any fish with an already compromised immune system can be attacked. Fish will lose the ability to resist attack when they are either very young or very old, under stress, already diseased, or experiencing malnutrition.

Bacteria capable of infecting a host will have different levels of pathogenicity as expressed by their virulence. Virulence is a measure of how many bacterial cells of a certain strain must be present in the host in order to elicit a response by the host in a certain amount of time. Another way of thinking about virulence is the ease with which bacterial toxins break down the tissues of the fish. Digestion of the fish provides nutrients that allow the bacteria to reproduce-increasing in number until they elicit a host response-occasionally, death. A highly virulent strain of bacteria can potentially kill a large number of fish in a short amount of time.  (continue reading here)

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