COPPER SULFATE CONTROLS FUNGUS ON MAT-SPAWNED LARGEMOUTH BASS EGGS

Copper sulfate (CuSO₄) is widely used by the catfish and hybrid striped bass industries as an economical treatment to control fungus (Saprolegnia spp.) on eggs; these industries use hatching troughs and McDonald jars, respectively, in moderate alkalinity waters.  This study determined the effectiveness of CuSO₄ on mat-spawned largemouth bass eggs at an extremely high alkalinity.  

Adult largemouth bass were placed in concrete vats and allowed to spawn on 60 cm² fiber mats.  Spawns were moved to 350 L plastic hatching containers within 12 h.  Efforts to dislodge eggs from spawning mats with bromelain were unsuccessful; other spawns were then cut into 10 cm² sections with a guillotine paper trimmer.  Sections were suspended in each aquarium and acclimated for 1 h in 18.3°C well water.  The study consisted of 3 CuSO₄ concentrations (10, 20, and 40 ppm) and an untreated control; there were 4 replicates.  Eggs were treated daily until fry began to descend from the mats.  Chemistry of the well water was pH 7.8, alkalinity 386 mg/L and hardness 455 mg/L.  Fungus was severe in the untreated controls, but only light to moderate amounts of fungus was present in treatment concentrations with 40 ppm having the best control.  Due to the adhesiveness of the eggs to the spawning mats, a quantitative analysis could not be done.  Benchtop toxicity studies have also been completed to determine the effect of CuSO₄ on sac and swim-up largemouth bass fry.