Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/10/2000
Publication Date: 11/1/2000
Citation: XU, D., KLESIUS, P.H., SHOEMAKER, C.A., EVANS, J.J. THE EARLY DEVELOPMENT OF ICHTHYOPHTHIRIUS MULTIFILIIS IN CHANNEL CATFISH TISSUE IN VITRO. JOURNAL OF AQUATIC ANIMAL HEALTH. 2000. Interpretive Summary: Ichthyophthirius multifiliis (Ich) is one of the most severe fish parasites. Ich attacks almost all species of freshwater fish at different growth stages, from young to adult fish. Diseases caused by Ich have been reported in various freshwater fishes worldwide and cause heavy losses of fish. Entire populations of fish can be destroyed within a few days if conditions are optimal for the diseases. The parasite burrows into the ski and gills and causes pin-head-size white spots. The parasitic trophont (young Ich) lives completely within fish. The host provides the parasite with food and other necessary substances for growth. The parasitic young Ich has to leave fish if host fish dies. Tissue culture can keep fish tissue alive in culture medium and may provide the necessary conditions for young Ich survival and growth. This study established tissue culture conditions suitable for studying attachment and early trophont development in culture tissues instead of using live fish. Theronts, an infective young Ich were added to freshly excised channel catfish fin, gill and skin tissues in culture medium. The early development of trophonts, including growth, rotation speed, attachment and survival rates were studied in different tissues and times. The results of this study showed that young Ich could develop in cultured tissues and the identification of parasite cellular extracellular substances is now possible.
Technical Abstract: Infective theronts of Ichthyophthirius multifiliis were added to freshly excised channel catish fin, gill and skin tissue culture preparation and established bluegill (BF-2) fin cells. The early development of trophonts, including growth, rotation speed, attachment and survival rates were studied in different tissues and times. Theronts usually swam in modes of increasing speed, bursting and wobbling within the first hour until contac was made with tissues. About 86 - 92% of the theronts attached to fish tissues in an enter and leave and re-enter pattern within the first 10 min. Theront attachment rates are more than 88% in fin, gill and skin 1 hour post exposure (PE). No attachment and shape transformation of theronts were observed on BF-2 cells. Rapid growth period of trophonts occurred in fish tissue in the first 4 h after addition to tissues. Trophonts grew to a size of 30.0 +/- 3.1 um 4 h PE in gills, an increase of 9.6% per hour. The growth rate of trophonts was 1.2% per hour in gills between 4 and 8 h. Trophonts grew slowly and increase 0.5% per hour in diameter between 8 - 48 h after addition to the gill. The majority of trophonts usually reached a size of 30 +/- 2.2 um at 2 h and 36.8 +/- 2.1 um at 8 h PE in skin and 31.7 +/-2.1 um at 2 h and 36.2 +/- 2.6 um at 24 h PE in fins. No difference in trophont rotation speed was found and was slower with an average of 819.3 +/- 195.7 um/min. Most trophonts were alive 8 h PE with survival rates higher than 97%. The mean survival rate was 67.8% at 24 h and 8.4% at 48 h PE in all tissues. This study established tissue culture conditions suitable for studying attachment and early trophont development in vitro.