Je. Bly et al., THERAPEUTIC AND PROPHYLACTIC MEASURES FOR WINTER SAPROLEGNIOSIS IN CHANNEL CATFISH, Diseases of aquatic organisms, 24(1), 1996, pp. 25-33
Winter saprolegniosis in channel catfish Ictalurus punctatus is associ
ated with low temperature (similar to 12 degrees C) induced immunosupp
ression and invasion by a ubiquitous, opportunistic water mold, identi
fied as a Saprolegnia sp. In this study, attempts were made to identif
y antimicrobials/chemicals which may (1) be effective for the therapeu
tic treatment of winter saprolegniosis, and (2) prophylactically contr
ol water concentrations of Saprolegnia and hence prevent the onset of
disease under laboratory challenge conditions. The antimicrobials used
were amphotericin B and the cecropins A, B, and P1. While amphoterici
n B halted Saprolegnia growth, the cecropins were ineffective. The che
micals and herbicides approved for use by the U.S. Food and Drug Admin
istration and considered in this study for the prevention of Saprolegn
ia zoospore production or cyst germination were used at concentrations
less than or equal to those recommended for use in commercial catfish
ponds for other purposes. Compared with malachite green (a positive c
ontrol only), sodium chloride and potassium permanganate were ineffect
ive, while copper sulphate and formalin inhibited both zoospore produc
tion and cyst germination. However, at the lowest inhibitory dosage, c
opper sulphate was toxic to catfish challenged under laboratory condit
ions; this was likely due to the low alkalinity of our lank water when
compared to that of catfish ponds. Several herbicides were tested inc
luding diquat, simazine, hydrothol 191, and aquathol K. Only diquat ha
d an inhibitory effect on Saprolegnia growth. In subsequent laboratory
challenge experiments, both formalin and diquat were efficacious in p
reventing the onset of winter saprolegniosis in channel catfish.