Submitted to: Global Aquaculture Advocate
Publication Type: Popular Publication
Publication Acceptance Date: 6/26/2016
Publication Date: 6/29/2016
Citation: Straus, D.L. 2016. Egg saprolegniasis in a commercial sunshine bass hatchery: Control regime developed using copper sulfate. Global Aquaculture Advocate. Available:http://advocate.gaalliance.org/egg-saprolegniasis-in-a-commercial-sunshine-bass-hatchery/.
Technical Abstract: An obstacle to sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) larval production is fungal growth on eggs caused by the water-mold Saprolegnia spp. Copper sulfate (CuSO4) is commonly used for fungus control in troughs of catfish hatcheries, but the effectiveness on other fish egg hatching systems was unknown. Because sunshine bass eggs begin hatching after 48 h, CuSO4 treatments (0, 10, 20, and 40 mg/L) began immediately the afternoon of spawning with a 10 min aerated, static bath and was 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. For the effectiveness experiment in 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 highest survival was at 40 mg/L CuSO4 (50.5 % survival); however, the 20 mg/L CuSO4 treatment (45.8 % survival) was not significantly different from the 40 mg/L treatment and 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 hLC50 values were 5.4 and 3.91 mg/L CuSO4, respectively; the No Observed Effect Concentrations (NOEC) 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 control of saprolegniasis in McDonald jars.