Abstract

Amyloodinium ocellatum, a dinoflagellate ectoparasitic on the gills and skin of marine and brackish-water fishes, is highly prolific and destructive in closed culture systems. The parasite reproduces successfully over a wide range of temperatures and salinities, and is extremely resistant to treatment with common fishery chemicals. The survival of Amyloodinium tomonts (encysted, reproductive stage) after prolonged exposure to fresh water, low temperature, and chlorine bleach, and the effectiveness of numerous antimicrobial and antiparasitic compounds in vitro against tomonts and dinospores (free-swimming, infective stage) were the subjects of the present study.

Tomonts divided and produced dinospores even after 6 wk of storage in fresh water; percent viability after storage was much greater in tap water than in distilled water alone or with added calcium or sodium salts. Tomonts also survived storage in seawater at 10 C for 9 wk and at 15 C for at least 12 wk. Tomonts were unaffected by immersion in a 1:2,500 dilution of liquid chlorine bleach for 24 h or a 1: 1,000 dilution for I h; a few tomonts divided and sporulated even after a 1-h exposure to 1:500 bleach.

Dinospores were immobilized within 24 h by quinine, quinacrine, chloroquine, primaquine, chiniofon, emetine, dehydroemetine, acriflavine neutral, nifurpirinol, chloramphenicol, sulfathiazole, pentamidine, amphotericin B, malachite green, methylene blue, benzalkonium chloride, Lugol's iodine, hydrogen peroxide, and formalin. They were not killed by copper sulfate alone or complexed with citric acid or EDTA, nor by furazolidone, nitrofurazone, sulfamethazine, chlortetracycline, ipronidazole, metronidazole, ivermectin, suramin, or difluoromethylomithine. Although several substances, including all three copper compounds, prevented or inhibited tomont division or sporulation during the 7-day treatment period, only five--formalin, chiniofon, pentamidine, ipronidazole, and malachite green--impaired reproduction permanently. The effectiveness of chemotherapeutic agents against the parasite in vivo, their toxicity to fish and nitrifying bacteria, and their persistence in culture water are still being studied.