A dirty system is a nightmare: foam, protozoans, dirty rotifers, and clogged screens and more. Fouling reduces capacity, reduces rotifer value, increases labor cost and makes harvesting difficult. Worse, fouling can lead to unhealthy bacterial flora. Dirty systems are usually the result of dirty feed or poorly set up culture systems.
Healthy (probiotic) bacteria
Bacterial counts in rotifer systems are always high; the higher the density and feed rate, the more bacteria.
Most bacteria are benefit the rotifer culture by metabolizing waste such as ammonia, producing vitamins and by consuming nutrients that could otherwise feed harmful and pathogenic bacteria. This benefit is known as the Probiotic Effect. A high population of strong beneficial bacteria will displace pathogenic bacteria to the point where they are not a problem. Most systems will develop their own bacteria populations without intervention. However, the addition of cultured probiotic bacteria is seen by many as an effective way to stabilize cultures.
Harmful but non-pathogenic bacteria
Bacteria are a critical element of all rotifer systems and most of the bacteria are helpful bacteria. However, it is not uncommon for rotifer systems to lose productivity with no clear indication as to why. Sometimes it is a leak or other mechanical problem but sometimes it is bacteria. When the wrong bacteria take up residence rotifer production can be cut by a third or more. Check the smell. It might smell different. Sometimes when a system is left alone to run normally the system will spontaneously re-invigorate itself weeks later. However, it never hurts to transfer the culture to a new system and sanitize the old one.
Vibrio species are ubiquitous. Most vibrio bacteria are harmless. A few vibrio species are pathogenic and cause identifiable disease. Often vibrio will cause digestive problems that do not rise to the level of “disease,” but result in diminished rotifer production and health and, when fed to the fish, poor growth and development of your larvae. If you think you have harmful bacteria and test for vibrio, be sure to use a protease-specific test for harmful vibrio bacteria. A simple vibrio test will almost always test positive.