I have been thinking about this for seven or eight years and finally, through scientific research and my experimentation I think I have figured out something that may change the way we run aquariums. For many years I have been feeding live blackworms, live amphipods and live new born brine shrimp to my tank and I always assumed the excellent health of my fish was a result of that. My fish seem immune from just about everything including bacterial infections and parasites. Although live food seems to be the reason for their immunity, I think I found out the exact mechanism for the immunity. It's not so much that the food is live, but that the bacteria inside the guts of the food is also live. Many of our fish are quarantined for 72 days, then put in a sterile tank and fed things like freeze dried worms, pellets, flakes and frozen food. Almost all of that food is sterile although frozen food "may" have some living bacteria, albeit weak. Fish in the sea eat nothing but live food along with it's associated gut and skin bacteria. New reasearch indicates that a fishes immune system, while vastly different from ours still depends on the fish meeting an infectious agent to impart immunity to the animal. Our immune system is mainly concentrated in our bone marrow but fish have no bone marrow and instead produce antibodies in their kidney and spleen. The bacteria on the food the fish eat filters through the kidney which helps the immune system recognize a threat. The immune response of fish is to produce slime which completely covers the fish and the slime contains "activated macrophages" Following are just "partial" quotes of this informative article that I have found which makes good reading especially to the many aquarists that don't believe fish can become immune from disease and parasites. I quoted some parts of the article that I thought were more suited to this post but it is incomplete and can be read in full if you Google the link starting with (ISRN ImmunologyVolume 2012 Maria Angeles Ref: Copyright © 2012 María Ángeles Esteban. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (ISRN ImmunologyVolume 2012 (2012), Article ID 853470, 29 pageshttp://dx.doi.org/10.5402/2012/853470Review ArticleAn Overview of the Immunological Defenses in Fish SkinMaría Ángeles Esteban) Quote: Immunity associated with the parasites depends on the inhabiting discrete sites in the host. Especially important for this paper are the ectoparasites, those habiting in or on the skin. Until recently there had been little direct evidence of innate immune mechanisms against parasites associated with mucosal epithelium . The active immunological role of skin against parasitic infection has been shown recently [286–288], and now mucosal immunity against them start to be elucidated. Non-parasitic fishes usually die following infection, but animals surviving sublethal parasite exposure become resistant to subsequent challenge. This resistance correlates with the presence of humoral antibodies in the sera and cutaneous mucus of immune fishes. According to these authors "probiotic for aquaculture is a live, dead or component of a microbial cell that, when administered via the feed or to the rearing water, benefits the host by improving either disease resistance, health status, growth performance, feed utilisation, stress response or general vigour, which is achieved at least in part via improving the hosts or the environmental microbial balance."The first demonstration that probiotics can protect fishes against surface infections was against Aeromonas bestiarum and Ichthyophthirius multifiliis in rainbow trout . The research on this topic is considered of high priority at present because enriched diets could be used as preventive or curative therapies for farmed fishes. End Quote Another interesting fact found in a recent issue of Scientific American By Ferris Jabr | September 12, 2012 | States that zebra fish whose guts were rich in bacteria absorbed more fats from their food as compared to fish in a germ free envirnment which in turn increased the number of energy-rich fat bubbles stored within the fish's intestinal cells for later use. I also discovered while researching is that fish fed a vaired diet actualy had less bacterial diversity in their gut than fish fed only one or two different types of food. I have always said that fish do not need a vaired diet, they need what they were designed to eat and nothing more. My fish are normally fed only three types of food. Live worms, frozen clams and frozen mysis. The smaller fish are only given live new born brine shrimp. I sometimes increase the diversity of their diet as an experiment but when that is over, they go back to their normal diet. Coincidently in this months "Popular Science" (August 2015) there is an article about this very topic. The author states that the most germ free envirnment today is on the International Space Station. Everything is sterilized including the air. All the surfaces are coated with bacteria limiting coatings, even the water is treated with iodine and biocidal nano silver so the only bacteria prsent are the ones coming from the astronauts themselves. They can't open a window or send out for Pizza so there is no fresh influx of microbes to balance the ecosystem. Sounds like quarantining doesn't it? He also states that a loss of gut bacteria correlates with many diseases and could impede longer space travel. If we lose our gut bacteria, our immune system goes dormant. In the real world bacteria, viruses and parasites evolved right along with other organisms that help keep each organism in check. They have their enemies and friends. When we mess with the system by using antibiotics or extended periods of quarantine, or remove living bacteria from their food, we are dooming the fish to a life where they are on the verge of getting a fatal disease. This is also the reason so many diseases are contracted in hospitals, a place where great pains are taken to keep the place clean. They are clean, so the only bacteria present are from sick people with no other bacteria or viruses to counteract them. It is now thought that people using those hand sanitizers from very young are at a higher risk of becomming an allergic toddler. Human babies born normally pick up Lactobacillus in the birth canal which helps them digest milk and lowers the gut's pH to the normal range. but babies born by C-section miss out and could be born with Staphlococcus and sometimes antibiotic resistant bacteria. (Rinku Patel Popular Science August 2015) So after researching all of this I have come to the conclusion that quarantining fish for an extended amount of time is actually very bad for our fishes health. In my opinion, if we want to quarantine I would do it using drugs such as copper in the theory that doing so will kill any parasites present in about 10 days while keeping the immunity the fish intact. Then I would feed at least some live food every day not just for the vitamins that come from live food, but for the bacteria. I am not sure how long a fishes immunity lasts but in the sea, it was immune, or almost immune for it's entire life. When a fish is collected, stored, starved and shipped it is in a very weakened state and their immune system is hardly functioning so even though the immune response to parasites, viruses and bacteria is there. It isn't strong enough to protect the fish, but if we can get it out of stress, fed live bacteria laden food and in a stable envirnment as soon as possable, it will recover and sustain some of their immunity. How many times do we read that a tank full of quarantined fish suddenly crashes and all the fish are lost to a parasite? It happens daily and all you have to do is go on any fish forum and search for it. Fish quarantined for extended amounts of time and fed sterile foods "have no immune system what so ever". I didn't make this up as you can read the articles I referenced or just Google "Fish Immunity" where you will find a plethora of new research which suggests that keeping fish sterile is the complete wrong thing to do. I rarely put references in my posts because I normally do my own research. But I realize I am not a fish doctor, researcher or marine biologist. What I am is an aquarist with immune fish. How do I know they are immune? I know because some of them have been in my tank for over 20 years, I add fish from many stores and even the sea. I can add fish with obvious parasites and in no case will anything else become infected. Many times during the year I add mud from the sea for the bacteria I always thought it was a good idea, now I know why. My fish get some live food every day and always have. I even think that the fish infected with parasites that I add strengthn the immune system so they never become infected. Of course we can't add parasite infected fish to a system that is not already immune and that is where the problem starts. . If this is not immunity I am an extreamly lucky individual and should go out and buy lottery tickets today.