Use of Copper Sulfate to Control Egg Saprolegniasis at a Commercial Sunshine Bass Hatchery

Abstract

AbstractAn obstacle to the larval production of sunshine bass (female White Bass Morone chrysops × male Striped Bass M. saxatilis) is fungal growth on the eggs caused by the water mold, Saprolegnia spp. Copper sulfate (CuSO4) is commonly used for fungus control in troughs at catfish hatcheries, but the effectiveness in other fish‐egg hatching systems is unknown. Because sunshine bass eggs begin hatching after 48 h, CuSO4 treatments (0, 10, 20, and 40 mg/L) began the afternoon of spawning with a 10‐min, aerated, static bath and were repeated the morning and afternoon of day 2; eggs were not treated after hatching began. An in vitro assay was developed for this treatment regimen that indicated maximum fungal inhibition was achieved with 20 mg/L CuSO4. In the effectiveness experiment in McDonald hatching jars (n = 3), fungus was severe in the untreated controls (27.7% survival), but very little fungus was present in treatments receiving 10 mg/L CuSO4 (31.4% survival) or higher. The control was not significantly different from the 10‐mg/L treatment. The highest survival was at 40 mg/L CuSO4 (50.5% survival); however, the survival from the 20‐mg/L CuSO4 treatment (45.8%) was not significantly different from that in the 40‐mg/L treatment and thus allows for a greater margin of safety. Fungus samples were identified as Saprolegnia ferax through genetic sequencing. Toxicity experiments on sunshine bass larvae indicated the 24‐ and 48‐h LC50 values were 5.4 and 3.9 mg/L CuSO4, respectively; the no observed effect concentrations were 0.5 and 0.25 mg/L CuSO4, respectively. This study confirms that CuSO4 can be an economical and valuable resource in hatchery management for the control of saprolegniasis on sunshine bass eggs in McDonald jars.