ICHTHYOPHTHIRIOSIS – CAUSE OF SIGNIFICANT LOSSES OF CARP FINGERLINGS

Ichthyophthiriosis is widespread parasitic disease of fi shes caused by a ciliated protozoan, Ichthyophthirius multifi lis. Th is parasite is capable of aff ecting most of species of freshwater fi shes, including all cyprinids. Th e parasites usually can be found on skin and gill in the form of white prominent spots 0.1-1 mm in diameter, which looks as if the fi sh was sprinkled with grits. Within these tissues, infections cause localized lymphocyte infi ltration, focal necrosis and varying degrees of epithelial proliferation. Investigations were carrieed out during a last 10 years, while monitoring the health condition of carp fi sh. Diagnosis of ichthyophthiriosis was performed by clinical and microscopic examination. Disease was present in carps throughout their life, but the most susceptible were young categories. Th e parasites were present on the skin and gills earlier in 10-day-old fi ngerlings. Th e outbreaks are most common in spring, aft er overwintering when water temperatures increase and also does the parasite replication rate. High stock density, water quality and poor condition contribute to illness. Since the disease causes signifi cant losses of carp fi ngerlings it is necessary to perform its adequate controls and therapy. In order to prevent the disease it is need to to rear young fi sh separately from other fi sh categories, prevent weed fi shes from entering the ponds and employ hygienic and prophylactic measures. All technological measures which can improve the condition of fi sh are most eff ective against ichthyophthiriosis. It is important to add lime into the pond from time to time. Eff ective chemical treatments for I. 1* e-mail: miroslavcirkovic@yahoo.com Arhiv veterinarske medicine, Vol. 8, No. 1, 3 12, 2015 Ćirković M. et al.: Ichthyophthiriosis – cause ...


INTRODUCTION
Ichthyophthiriosis, also known as ich or white spot disease is a cosmopolitan parasitosis of fi shes (Nigrelli et al., 1976;Valtonen and Keränen, 1981).Infections have been reported from all regions where fi shes are cultured, from the Equator to the Arctic Circle (Rinramaki-Kinnanen and Valtonen, 1997;Valtonen et al., 1994).I. multifi liis is believed to have originated as a parasite of carp (Hoff man, 1999).Ich appears to parasitize all freshwater fi shes.Th ere are no records of species with complete natural resistance (Ventura and Paperna, 1985).Ichthyophthirius multifi lis is the largest known parasitic protozoan found on fi shes.Adult organisms are oval to round and measure 0.3 to 1.0 mm in size and can be visible by the naked eye.Th e adult is uniformly ciliated and contains a horseshoe-shaped nucleus which can be seen in older individuals.Parasite has a simple life cycle consisting of three developmental stages each of which is ciliated: the infective form (theront), the host associated form (trophont) and the encysted environmental form (tomont) (Hines and Spira, 1973).Th e motile theront (30 x 60 μm in size) has limited energy reserves and remains infectious for approximately three days (Dickerson and Dawe, 1995).It penetrates under the epithelium, feeds on cells and tissue fl uids and transforms into the next stadium -trophont (Ewing and Kocan, 1986).When fully developed, trophonts abandon the host and transforms into tomonts.Th e life cycle of I. multifi liis is infl uenced by water temperature.A single round of replication occurs in 4-5 days at water temperatures of 20-24°C (Ewing et al., 1986).Th e parasite cannot survive in water temperature greater than 30°C.At colder temperatures (<10°C) parasite development is slowed.Epizootics usually occur during spring and summer months when warmer water temperatures increase parasite replication rate and reduced levels of dissolved oxygen cause stress in fi sh populations (Maki, 2002).Other factors infl uencing the severity of infection include stocking density, water quality, and susceptibility of various fi sh species (Johnson, 1993).Lesions associated with I. multifi liis infection have been well characterized.Th e classic sign of infection is presence of small white spots on the skin or gills 0.1-1 mm in diameter.Prior to the appearance of white spots, fi sh may show signs of irritation, fl ashing, weakness, loss of appetite, and decreased activity.If the parasite is only present on the gills, white spots will not be seen at all, but fi sh will die in large numbers (Francis-Floyd and Reed, 1991).In these fi sh, gills will be pale and very swollen.Th e diagnosis is established by light microscopy, when the parasites are found in fresh skin and gill samples (Francis-Floyd and Reed, 2011).Th omits are continuously moving, while the trophonts are located cysts.In order to prevent the disease it is need to to rear young fi sh separately from other fi sh categories, prevent weed fi shes from entering the ponds and employ hygienic and prophylactic measures (Ćirković and Novakov, 2013).Th e most used chemical treatments for I. multifi liis include copper sulfate, potassium permanganate, malachite green, salt and formalin (Johnson, 1993).Commercial aquaculture operations are limited to using only those compounds approved for food fi sh and are hampered by the cost of treating large volumes of water for extended periods of time.Th e goal of this paper is to do a survey of ichthyophthiriosis in carp fi sh pond, of Serbia and to indicate the importance of the disease, as well as to perform and recommend the most appropriate preventive and therapeutic measures.

MATERIALS AND METHODS
Diagnostics and investigations were conducted during last 10 years, while monitoring the health condition of carp fi sh.Over a 10-year period more than thousands of samples were examined for the presence of Ichthyophthirius multifi lis.Th e examined fi shes originated from 18 common carp fi sh ponds in Serbia.Fish were collected with a net and suspected fi sh were transported alive to the laboratory where they were processed.
Samples for microscopic examination were taken from tissue of gill arch, the body surface and a tail fi n.We removed several white spots from an infected fi sh, then mount them on a microscope slide with a few drops of water and a cover glass.Th e mature parasite is the large (200 to 800 μm) ciliated trophonts which were easily seen in unstained wet mounts (× 10-40 magnification).Th e trophont of Ichthyophthirius multifi lis has a distinctive horseshoeshaped nucleus, which is a pathognomonic sign of infection.In early or very heavy infections, theronts were also present.

RESULTS AND DISCUSSION
During the investigations(study) Ichthyophthirius multifi lis (Figure 1) was present in all carp categories, but the most susceptible were carp fi ngerlings where in some ponds mortality ranged up to 90%.Th e parasites were present on the skin and gills in 10-day-old carp fi ngerlings earlier.Th e outbreaks were most common in spring, aft er overwintering when water temperatures increased as well as parasite replication rate, but the fi sh immunity is still weaker.Also, the disease was present in ponds with high stock density, lower water quality and poor condition which contributed to the illness.At the beginning of the disease there were no visible changes in the fi sh behaviour, but as the infection intensifi es the fi sh were agitated, moving quickly to the water surface, swiming in circles and were less reactive to external stimuli.Fish infected with I. multifi liis demonstrated an aberrant behavior called "fl ashing" (i.e., darting or making quick movements against objects in their environment).Th is behavior may be seen early in infection before parasites are visible on the exterior surface of the fi sh.On the skin there were necroses in the form of white spots 0.1-1 mm in diameter, which looks as if the fi sh was sprinkled with grits (Figure 2).Intense infections resulted in death, when fi sh died in large numbers, especially when parasites were present on the gills, which were pale and very swollen, so asphyxia was the cause of the death.Lesions made by parasites may become infected with bacteria and especially fungi of which saprolegnia being the most frequent one (Figure 4).Ichthyophthiriosis is highly important disease because is one of the most common diseases in freshwater fi shes and can cause mortality rate up to 100% (Meyer, 1974;Maki, 2002;Ćirković and Novakov, 2013).Mild infections may resolve without treatment, but in closed systems multiple rounds of replication usually result in heavy parasite loads and high mortality.Infected fi sh oft en die due to impaired respiration and disrupted osmoregulation (Hines and Spira, 1974).Disease control and prevention in an intensive fi sh production is the most important and depend upon an integrated management program.Th e basic is to prevent the fi sh from the exposure of the parasites, identify the disease if it occurs and perform treatment of infected fi shes.
In order to prevent the disease it is necessary to rear young fi sh separately from other fi sh categories and prevent weed fi shes from entering the ponds.Th is is because fi sh which contracted the disease are the source of the infection as well as some weed fi sh species.Also all hygienic and prophylactic measures are necessary combatting this disease.All technological measures which can improve the condition of fi sh (nutrition, reduction of stress, good water quality) are eff ective against ichthyophthiriosis.It is also important to add lime into the pond from time to time.Eff ective chemical treatments for I. multifiliis include copper sulfate, potassium permanganate, malachite green, salt and formalin (Francis-Floyd and Reed, 2011; Johnson, 1993).Malachite green is a teratogen, and prohibited for use.Copper sulfate must be taken into consideration since copper sulphate is toxic at low pH and can diminish the oxygen content in water and lead to lethality.If the alkality is less than 50 ppm the application of copper sulphate is not advisable (Watson and Yanong, 2011).Copper sulfat, potassium permanganate and formalin are also under currently reviewing for the use as parasitic ides in food fi sh.So that, Non-iodized salt is the only permitted and safe therapeutic for use.Salt can be used to control white spot disease in small volumes of water.(i.e., tanks or vats).Fish can be dipped in a 3% (30,000 mg/l) solution for thirty seconds to several minutes, or they can be treated in a prolonged bath at a lower concentration (0.05% = 500 mg/l) (Francis-Floyd and Reed, 2011).

CONCLUSION
Ichthyophthiriosis is one of the most common diseases in freshwater fi shes.White spot disease were present on the skin and gills in 10-day-old carp fi ngerlings earlier, and caused mortality rate up to 90%.Th e outbreaks were most common in spring and connected with high stock density, lower water quality and poor condition.Characteristic white spots 0.1-1 mm in diameter, were present on the skin of infectede fi sh.Separate breading of carp fry from older fi sh categories, disable the entrance of wild fi sh, technological measures (optimal density, feeding, reduction of stress, good water quality) and lime addition are necessary for combatting this disease.Using of non-iodized salt is also eff ective in the control of the disease.

Figure 3 .
Figure 3. Ichthyophthiriosis in a carp-secondary infection with fungi of Saprolegnia species