The early development of Ichthyophthirius multifiliis in channel catfish in vitro

This study established ex vivo conditions suitable for studying early troph ont development in excised tissues of channel catfish Ictalurus punctatus w ithin the first 48 h. Infective theronts of Ichthyophthirius multifiliis we re added to freshly excised channel catfish fin, gill, and skin and establi shed fin cells (BF-2) of bluegill Lepomis macrochirus. The early developmen t of trophonts, including growth, rotation speed, attachment, and survival( %), was studied in different tissues and at different times. In all, 86-92% of the theronts attached to fish tissues in an enter, leave, and reenter p attern within the first 10 min. Theront attachment was more than 88% in fin s, gills, and skin I h post exposure (PE). Attachment and shape transformat ion of theronts were not observed on BF-2 cells. Trophonts grew to a size o f 30.0 +/- 3.1 mum in diameter 4 h PE in the gills, an increase of 9.6%/h. The size increase of trophonts was 1.2%/h in the gill between 4 and 8 h. Tr ophonts grew slowly and increased in diameter 0.5%/h from 8 to 48 h after a ddition to the gills. The mean volumes of trophonts at 1, 24, and 48 h PE i n gills were 1,072.6 +/- 3,131.6, 20,373.6 +/- 8,357.4, and 28,102.3 +/- 4, 740.0 mum(3), respectively. No difference in trophont rotation speed was fo und in different tissues between 1 and 24 h PE. At 48 h, the rotation speed of trophonts was significantly slower (P < 0.01); the average speed was 81 9.3 +/- 195.7 <mu>m/min. Most trophonts were alive 8 h PE; survival was hig her than 97%. The mean survival was 67.8% at 24 h and 8.4% at 48 h PE in al l tissues. The viability of excised tissues without theronts was considerab ly higher than that in tissues with theronts after 48-72 h in culture.