Process for the protection of fish and invertebrates and all their stages of development against or for the treatment of mycoses caused by fungi of the genera Saprolegnia, Aphanomyces, Achlyaflagellata and other species important in aquacultures by use of 2-[[[[1-[3-(1-fluoro-2-phenylethyl)oxy]phenyl]ethylidene]amino]oxy]methyl]alpha-(methoxyimino)-N-methyl-alphaE-benzeneacetamide, amisulbrom, cyazofamid, enestrobin, famoxadone, fenamidone, fluoxastrobin, orysastrobin, picoxystrobin and pyribencarb. This use leads to an inhibition or destruction of pathogenic fungi.The composition, comprising at least one fungicide selected from the abovementioned group for use in fish fanning and keeping is suitable for the prophylaxis and therapy of diseases of fish in aquaculture, in breeding ponds, breeding tanks, aquariums, natural stretches of game fish waters, ponds, and marine fish farms. Addition to the water and feed and direct application are the associated use forms. The addition of the composition according to the invention to the water decreases fungal infections of spawn and fish.