TREATMENT OF FISH PARASITES .9. EFFECTS OF A MEDICATED FOOD CONTAINING MALACHITE GREEN ON ICHTHYOPHTHIRIUS-MULTIFILIIS FOUQUET, 1876 (HYMENOSTOMATIDA, CILIOPHORA) IN ORNAMENTAL FISH

For systemic therapy against trophozoites of the skin-inhabiting stage of Ichthyophthirius multifiliis in ornamental fish, the latter were f ed medicated food flakes containing malachite green once daily for 1-1 1 days ad libitum. Naturally or artificially infected cardinal tetras (Paracheirodon axelrodi), blue gouramis (Trichogaster trichopterus), o r clown loach (Botia macracantha) were used in the trials. The fish we re maintained in aerated 12.5- or 60-1 aquaria at 23-degrees-C. Ultras tructural investigations (scanning and transmission electron microscop y) revealed clear deleterious effects of malachite green on the parasi tic stages. Following the initial application, the inner membrane of t he mitochondria was destroyed. In fish fed for 2 days, aggregation of the mucocysts and polymerization the microtubules within the macronucl eus occurred. Finally, the trophozoite's membrane was completely destr oyed. In fish fed for 4 days, the medicated food killed all trophozoit es of I. multifiliis. Sensitive ornamental fish (e.g., P. axelrodi) sh owed no adverse effects after they had been fed with only the medicate d food flakes for 2 months. Therefore, the oral administration of mala chite green using this newly developed medicated food considerably red uces the risk of toxic effects on the fish hosts, which are sometimes caused by malachite green following its application by immersion thera py. The feeding of flakes medicated with malachite green provides an e asy-to-handle and highly effective treatment of I. multifiliis in orna mental fish.