Effects of 3,N-methylglucamine lasalocid on Amyloodinium ocellatum

Abstract

The cosmopolitan nature of Amyloodinium ocellatum insures the constant possibility of an epizootic in high density mariculture facilities Chemotherapeutics have shown variable results against the parasite and none are currently approved for use in food fish. The ionophorous antibiotic lasalocid is currently approved for food animal use for the treatment and prophylaxis of coccidian protozoa. The sodium salt of lasalocid was converted to a water-soluble 3,N-methylglucamine salt to evaluate its therapeutic potential for amyloodiniosis. Tomonts and trophonts were incubated in saltwater containing antibiotics (penicillin 100 IU ml-1, streptomycin 100 μg ml-1) and 100 to 0.001 ppm concentrations of 3,N-methylglucamine lasalocid (3NMG-lasalocid). The 24 h tomont division rate and in vitro trophont density decreased in a dose-dependent manner when exposed to 3NMG-lasalocid concentrations between 100 and 0.001 ppm. Motile dinospores did not excyst until the 3NMG-lasalocid concentration was reduced to 0.001 ppm, and then at a concentration 44% that of controls. Cracked and ruptured tomonts were observed by scanning electron microscopy and degenerated internal membranous structures of trophonts were observed by transmission electron microscopy. Trophont infection on 0.5 to 1g red drum Sciaenops ocellatus fry exposed to 2.5 dinospores ml-1 in 6.0 1 of saltwater was reduced by 80% on gill filaments and 54% mm-2 surface area when treated with 0.1 ppm 3NMG-lasalocid. Infection was prevented at 1.0 ppm 3NMG-lasalocid.