Quarantine is a diverse topic and one which cannot adequately be covered in a single post. It is a dynamic concept but one which is extremely valuable and which should be considered as a priority when purchasing ANY fishes for your home aquarium.
One of the most common problems associated with the introduction of new fishes is the introduction of their parasites which they may be carrying into your system. Of all the many problems, parasites pose one of the most important because many of them have the ability to reproduce quickly in a closed system using a single host to close their life-cycle. These parasites (those with a direct life-cycle) have the ability to be the most destructive. To begin with however, we need to try and understand what happens when a seemingly healthy fish is introduced into your home tank and shortly thereafter you have an infestation.
Parasites are incredibly well adapted organisms and demand much respect. Most are highly specialised and have evolved to fill a very specific niche so narrow that some are only found in a single micro-habitat in or on a host, on a single host species, without which they would cease to exist. Parasites and their hosts are constantly in a battle to survive. Parasites are evolving ways of evading the host immune system, while host fishes are evolving ways to exclude their parasites. This constant conflict, often referred to as the “parasitic arms race” reflects what is known as the Red Queen Hypothesis which states that in order to survive, these organisms are constantly having to “run on the spot to keep up.” So, there is an intricate balance then between the host, the parasite and the environment which may or may not lead to the outbreak of disease. This balance is called the host-parasite dynamic. If we look at each of these as factors, we can take a deeper look and get a deeper understanding of how each influences this dynamic.
Factor 1: Host (A fish population being invaded by a parasite has 3 mutually-exclusive cohorts that can change in relation to one another during the course of disease.)
- The susceptible group: those than can become infected
- The infected group: those susceptible, now infected
- The removed or immune group: acquired immunity or death
Factor 2: Parasite
- The ability to infect a particular host species
- The parasite’s level of infectiveness (its pathogenicity)
- The parasite’s virulence
- The mode of parasitism
- Parasite or parasitoid?
Factor 3: Environment
- The environment can have a significant influence of the transmission and the development of disease
- Population density is critically important in the dissemination of disease
- Frequency of contact between the infected and susceptible hosts individuals (direct and indirect contact)
- Reduced host spatial arrangements and improved likelihood of successful invasion by re-infective stages
- Temperature, water quality, chemicals, water flow
- Stress and immunosuppression
Quarantine, the word, traditionally means isolation for 40 days. However, quarantine as we know it is often the isolation of new acquisitions or sick fishes from a healthy population to reduce the risk of introducing disease from individuals of the infected group to the susceptible group. All wild-caught fishes have parasites. When they are collected from the wild they are often maintained in small tanks with high stocking densities, increasing the risk of not only parasitic transfer between individuals, but also the frequency and success of transfer to individuals that are stressed and have a compromised ability to deal with infections through the immune system. In addition, water quality (particularly temperature) can play an important role in speeding up parasite life-cycles which puts additional strain on the frequency of successful invasion. Often, by the time you receive your fishes from a supplier, if they have not been adequately and CORRECTLY quarantined, they pose a significant risk of infection to your fishes if directly introduced. Here, prevention is the most effective action. A quarantine tank, completely separate from your main setup is invaluable because the period of isolation will allow for the manifestation of disease symptoms and therefore allow you to make a correct diagnosis which is imperative in choosing the correct treatment. You may also treat your fish before they exhibit any symptoms prophylactically, and after a period of at least 30 days in isolation with treatment can be considered of low risk to be introduced into your main tank.
Bear in mind that unless all of your fishes have been introduced this way, you may have a resident population of a parasite living comfortably within the realms of the dynamic equilibrium in your tank until this equilibrium is disturbed with the introduction of a new individual. It is common for a
Cryptocaryon irritans infection for example to be present without exhibiting any symptoms of disease, but will be ticking over while being “managed” by the immune system of the various host fishes. The introduction of the new fish presents a susceptible individual which allows for a shift in the equilibrium and therefore the likelihood of the onset of disease. This often begins with the new individual but could then again spread to the others until the equilibrium is again satisfied.
So, given that I am rambling on a bit here, DO quarantine your new fishes. It reduces but does not exclude risk. How to quarantine? This is another long and complicated affair and deals with diagnosis, specific treatments that are tolerant of specific host species and an understanding of IPM (integrated parasite management). One also needs to consider the risks and assign priorities to certain conditions, but here are some basic pointers:
- Treat separate purchases of fishes separately and do not mix quarantine periods to add new fishes or break treatments
- Treat ubiquitous parasites (those of low host-specificity) with priority
- Ensure that your quarantine system is completely separate from your main system and use a separate set of nets and cleaning equipment for each
- Keep low levels of light in the quarantine tank with some structures for fishes to hide in
- Do not have substrate in your quarantine tank. This can harbour parasites and can also absorb some chemicals from treatments
- Ensure your climate control is tight (no wild fluctuations in temperature or general water quality). Use a filter that can maintain your water quality but one which can be used with treatments
- Feed good quality foods but keep to a minimum to avoid poor water quality
- Keep records of your quarantine periods, species quarantined, where they came from and any observations which you made that may be useful in future
The various treatments available are as diverse as the problems they treat. Ensure that whatever treatment covers the life-cycle completion time of a known parasite (if you know what you are treating for) or at least the prescribed 30 days of prophylaxis. Some home-aquarist remedies make interesting claims about their products working in a short period of time. These are often inaccurate because parts of disease life-cycles are treatment resistant and these treatments are usually only treating for the symptoms and will not address the root cause of the disease. I always treat for 30 days, with water volume re-treated daily after a complete water change, this or through an IPM strategy given the biological parameters of a know parasite and the effects of the captive ecology on the biology. This is complicated but I can go into more detail again in subsequent posts.
I hope that the above gives a basic introduction to quarantine but I find that an understanding of the question “why?” is often the most valuable – so keep asking this question until your queries are satisfied. Let’s together take quarantine and its many facets to the endth degree.
Regards
David
