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Treatment of fish parasites

9. Effects of a medicated food containing malachite green onIchthyophthirius multifiliis Fouquet, 1876 (Hymenostomatida, Ciliophora) in ornamental fish

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For systemic therapy against trophozoites of the skin-inhabiting stage ofIchthyophthirius multifiliis in ornamental fish, the latter were fed medicated food flakes containing malachite green once daily for 1–11 days ad libitum. Naturally or artificially infected cardinal tetras (Paracheirodon axelrodi), blue gouramis (Trichogaster trichopterus), or clown loach (Botia macracantha) were used in the trials. The fish were maintained in aerated 12.5- or 60-1 aquaria at 23°C. Ultrastructural investigations (scanning and transmission electron microscopy) revealed clear deleterious effects of malachite green on the parasitic stages. Following the initial application, the inner membrane of the mitochondria was destroyed. In fish fed for 2 days, aggregation of the mucocysts and polymerization the microtubules within the macronucleus occurred. Finally, the trophozoite's membrane was completely destroyed. In fish fed for 4 days, the medicated food killed all trophozoites ofI. multifiliis. Sensitive ornamental fish (e.g.,P. axelrodi) showed no adverse effects after they had been fed with only the medicated food flakes for 2 months. Therefore, the oral administration of malachite green using this newly developed medicated food considerably reduces the risk of toxic effects on the fish hosts, which are sometimes caused by malachite green following its application by immersion therapy. The feeding of flakes medicated with malachite green provides an easy-to-handle and highly effective treatment ofI. multifiliis in ornamental fish.

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C :


CD :

core of electron-dense material

CY :


DV :

digestive vacuole

E :


EG :

electrondense granules

EL :

electron-lucent hole

F :


FL :

focal lysis of the cytoplasm

HA :

heterochromatin aggregation

HG :

heterophilic granulocyte

I :

interruption of the outer membrane

IM :

inner alvcolar membrane

K :

knobbed end of a cilium

LC :


MA :


MC :


MI :


MN :


MT :


MU :


N :


NG :

neutrophilic granulocyte

OB :

ovoid body

OM :

outer alveolar membrane

PP :

pseudopodial protrusion

PS :

parasomal sac

R :


T :


V :

vacuolization caused by treatment

VA :



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Schmahl, G., Ruider, S., Mehlhorn, H. et al. Treatment of fish parasites. Parasitol Res 78, 183–192 (1992).

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