Aquarium Fish: News From The Warfront With Cryptocaryon irritans, Part Five Of Five
This is the fifth and final installment in a series of articles. Part four covered some alternative methods or treatments for combating Cryptocaryon irritans. Part five continues detailing the aspects of immunity or partial immunity to Cryptocaryon irritans, low salinity variants of the parasite, the adaptability of marine teleost fish to hyposaline conditions, challenges to improving the transfer method of treatment and overcoming the difficulties associated with the transfer method. It also covers a new variation of the transfer method, changes in the transfer method that reduce stress and improve the survivability of treated fish, four steps to improve the "hypo-trans" method and some tips for reducing stress in fish.
Immunity or partial immunity
Fish that have survived a challenge with Cryptocaryon irritans can develop some level of acquired immunity for up to six months (Burgess & Mathews, 1995b). Some fish will not develop any protection or acquired immunity. Fish maintain immunity by the presence of the parasite without evidence of pathological lesions. However, many fish are not completely protected and can sustain a low level infection (Colorni & Burgess, 1997). This may account for outbreaks at a later date since the parasite was not eliminated from the system. Stress can diminish the fish's immunity, enabling the parasite population to increase, resulting in a renewed outbreak (Colorni & Burgess, 1997). Immunity or partial immunity may also explain why some of the inconsistently effective treatments previously mentioned appear to work at times.
The ability of fish to develop some level of immunity to Cryptocaryon irritans suggests that an immunological approach such as vaccination may be feasible. However, such a vaccination has yet to be developed.
Another possible approach is to employ a biological defense modulator such as Beta 1,3D glucan (Bartelme, 2003c). Beta glucan has proven to enhance the overall defense mechanisms of the immune system against bacterial, viral, fungal and parasitic pathogens. It has also been shown to work as an immune system stimulant when administered orally to fish. However, it has not been the subject of clinical trials specifically as an agent to combat cryptocaryonosis. Immuno-stimulants such as Beta glucan warrant further investigation.
Adaptability Of Fish To Hyposaline Conditions
Marine teleost fish are more euryhaline than previously believed (Wu & Woo, 1983).
Studies indicate that many reef fish which have been classified as stenohaline exhibit considerable powers of euryhalinity (Wu & Woo, 1983. Woo & Chung, 1995). Physiological assessment indicates that a species may be physiologically euryhaline while ecologically stenohaline. This suggests that the assignment of a species as euryhaline or stenohaline should be dissociated from a consideration of the ecological habitat of the species (Woo & Chung, 1995).
Ancient seawater concentration was believed to be much lower (404mm) than that found today (1123mm) (Spaargaren, 1979). It is likely that future coral reef inhabitants evolved in an environment that was much less saline than present day seas (Moyle, & Cech, 1982). This may account for the ability of marine teleost fish to readily adapt to hyposaline conditions.
Low Salinity Variants Of Cryptocaryon irritans
Presently, the transfer method is only alternative to copper treatment known to be consistently reliable against low salinity variants of Cryptocaryon irritans. The inherent problems with this method are the risk of injury and stress imposed on the fish from continuous handling. Refining or modifying this method in a way that reduces the risk of injury and minimizes the stress imposed on the fish would make the treatment safer and improve survival rates. The question is how can this be accomplished?
Challenges To Improving The Transfer Method
Plasma catecholamine concentrations can remain high for days after fish have been stressed (Mazeaud, et, al., 1977. Mazeaud & Mazeaud, 1981). Hydromineral or osmotic disturbance is an inherent part of stress in fish (Bartelme, 2000a. McDonald & Milligan, 1997). Stress causes the loss of water and influx of ions in saltwater fish. Conversely, stress causes the influx of water and loss of ions in freshwater fish (Folmar & Dickhoff, 1980. Mazeaud, et. al., 1977). The initial severity of a stressor such as handling and transfer determines the degree of osmotic disturbance rather than the duration of that stress (McDonald & Milligan, 1997).
Stress interferes with macrophage function and other immune system processes in general (Bartelme, 2003c). When immune function is inhibited fish become more susceptible to disease (Pickering & Pottinger, 1989. Rottmann, 1992). These disease problems can be delayed 1 to 3 weeks after a stressful event. This is could lead to the death of fish in what is known as the "Delayed Mortality Syndrome."(Noga, 2000) Netting and removing fish from the water is highly stressful (Bartelme, 2003b). Exposure to air for thirty seconds after exercise significantly increases mortality rates and blood lactate concentration in fish (Ferguson & Tufts, 1992. Wood, et. al., 1983).
Overcoming Difficulties Associated With The Transfer Method
Reducing the gradient between the internal fluids of fish and the surrounding ambient water alleviates water and ion disturbance ((Wedemeyer, 1996). Energy that would otherwise be consumed in osmoregulation is conserved making more available for other normal bodily functions such as maintaining normal homeostasis. Using hyposaline water conditions in combination with the transfer method will reduce the consequent stress of transfer and handling. (Wedemeyer, 1972. Murai, et al., 1979).
Pretreating fish with an immune system stimulant such as Beta 1,3D glucan will help them to proliferate the production of macrophage and enhance major host defenses of the immune system (Bartelme, 2003c). Orally administrating Beta glucan will stimulate immune function, helping fish to overcome or avoid infection. Animal studies indicate that Beta glucan is safe to administer in a wide dosage range. A dosage of 4mg/lb. per day is recommended.
Netting and chasing fish during capture are frequent sources of injury and stress (Bartelme, 2003b). Fish cannot easily see clear polyethylene bags or specimen containers that can be used instead of nets for capture, transfer and handling (Spotte, 1993 & 1979). Since the fish cannot see them, capture should be quicker and safer. The fish will also be less likely to become exhausted trying to avoid capture. Removing fish from their native environment (water) is highly stressful and often causes injury (Ferguson & Tufts, 1992. Flagg & Harrell, 1990). Fish captured in a clear plastic bag or specimen container never have to be removed from water during transfer and handling (Kreiberg, 1994).
A New Variation Of The Transfer Method
The new or hybrid method that I am proposing incorporates two proven treatments, used in combination, for eradicating Cryptocaryon irritans: hyposalinity therapy and the transfer method. I will refer to this as the hyposaline transfer or "hypo-trans" method. This consists of moving the fish between two hyposaline aquariums once every third day for a total of four moves. After each move, the empty tank is then cleaned and dried.
Fish should be placed in a quarantine tank with water parameters that match the aquarium that they were taken from. After the fish have been moved into the quarantine tank, begin acclimating them to reduced salinities in four stages using buffered freshwater. Take care to closely match the water temperature with each water change. Make two water changes a day for two days beginning the first day that the fish are moved into the treatment container. Reduce the salinity approximately 5ppt with each water change until the salinity has reached 13-14ppt.
The alkalinity and pH tend to fall in diluted saltwater. Check these parameters daily and add a buffer as necessary to maintain the pH within the 8.1 to 8.3 range. Feed lightly during treatment to help preserve the water quality.
Hyposalinity has proven to be a viable therapy for cryptocaryonosis, but this treatment will not be effective against low salinity variants of Cryptocaryon irritans. Here, hyposaline conditions are employed as a means of alleviating the stress and consequent osmoregulatory disturbance caused by repeated capture, handling and transfer when using the transfer method. Drying is what actually destroys the tomonts that are left behind each time that the fish are moved. This new method will work regardless of the salinity tolerance range of any particular variant of Cryptocaryon irritans without employing harsh or dangerous agents such as copper.
Changes In The Transfer Method That Reduce Stress And Improve Survivability
- Twenty-four hours before starting treatment using the hyposaline transfer method the fish are pretreated with Beta 1,3D glucan. This will proliferate and activate biological defense mechanisms prior to handling and potential injury.
- Fish are handled and captured in a manner that reduces stress, minimizes the risk of injury and they are not removed from their native environment during these processes.
- Water with a salinity of 13 to 14ppt is used to reduce the gradient between the internal fluids of fish and the surrounding ambient water. This alleviates the effects of handling, capture and transfer with the subsequent hydromineral or osmotic imbalance.
Four Steps To Improving The Hyposaline-transfer Or "hypo-trans" Method
- Fish are pretreated with Beta 1, 3D glucan 24 hours prior to being moved to stimulate immune function and increase biological defense mechanisms. Continue to administer Beta glucan in the food daily throughout the entire duration of the hyposaline transfer method of treatment.
- Fish are captured and transferred using clear polyethylene bags or plastic containers.
- Fish are transferred water to water without exposure to the air.\
- A reduced salinity is employed in the treatment tanks as a means of counteracting any hydromineral or osmotic disturbance caused by the stress of handling, capture and transfer in saltwater fish. Conversely, adding salt to the water with freshwater fish accomplishes the same thing (Wedemeyer, 1996).
Other Tips To Reduce Stress
Premix a large batch of saltwater at least 24 hours before beginning treatment. Mix enough water for all the water changes you will be making during the treatment. Water that has been well mixed and aerated for at least 24 hours prior to use will be more completely dissolved and chemically stable. Raw, or poorly mixed saltwater is irritating to delicate gill tissues and stressful to fish.
Place the treatment aquariums in a quite place away from areas where there will be a lot of movement or noise. Supply the fish with plenty of PVC pipe in the treatment tanks for hiding places. Another way to reduce stress in fish is to decrease their awareness of what is going on in and around the aquarium (Bartelme, 2000b). Painting the back, bottom and sides of treatment tanks will reduce the fish's awareness of the surrounding environment. Keep the lighting dim.
Add Pro Tech Coat Marine™, or another polymer (polyvinylpyrrolidone or PVP) to the water to serve as a temporary barrier in the event that the mucus/skin/scale barrier is compromised. This helps to mitigate the stress from capture and transfer (Carmicheal and Tomasso, 1988). A chemical filtration pad such as Poly Filter™ by Poly Bio Marine can be used to reduce impurities, such as ammonia, that may build up in the treatment tank.
A greater understanding of the life cycle, mode of transmission and treatment of Cryptocaryon irritans substantially reduces the threat of losses suffered in maraculture and by hobbyists alike. Cryptocaryon irritans is adapting to new environmental conditions making the development of new, innovative treatments and methods for its control crucial. It is essential that the efforts to develop practical, effective treatments for the control of Cryptocaryon irritans continue. As our knowledge and understanding increases, new gains will be made in the war against Cryptocaryon irritans.
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