Abstract

The anti-oomycetic effects of sodium chloride and potassium permanganate on the vegetative and zoosporic stages of Achlya sp. BKKU 0502, Saprolegnia diclina BKKU 0506, Aphanomyces sp. BKKU 0508, Achlya ambisexualis BKKU 0615 and Achlya bisexualis BKKU 0616 were investigated at 25°C.  The results showed that the exposure of the samples to 3.0 and 2.5% sodium chloride for 24 h was toxic to the vegetative and zoosporic stages, respectively. Moreover, 200 and 25 ppm of potassium permanganate were effective at killing the vegetative stage at 24 h and the zoosporic stage at 1 h, respectively. The toxicities of 2.0, 2.5 and 3.0% sodium chloride for controlling oomycete activity were determined using tilapia (Oreochromis niloticus) eyed eggs for both 1 and 24 h treatments.  The results showed that salt concentrations at levels of 2.0% or higher reduced the hatching rate percentage of the treatment groups to a value significantly different from that of the control group (P<0.05).  A noteworthy result was that the 3.0% sodium chloride treatment for 24 h produced a 0% hatching rate. The treatment of the eyed eggs with 100, 150 and 200 ppm potassium permanganate to control the oomycete activity had a highly toxic effect on the eggs: the results showed a 0% hatching rate for all of the treatment groups after 1 and 24 h exposures.  Therefore, it is not possible to use sodium chloride or potassium permanganate to prevent the activity of oomycetes on tilapia eggs because these two chemicals decrease the hatching rate. Other chemicals that may be safe to use on other edible aquatic organisms will require further investigation.

Key words: Sodium chloride, potassium permanganate, oomycete zoosporic stage, vegetative stage, tilapia eyed eggs.