Inhibiting fungus on largemouth bass eggs with copper sulfate and its toxicity to fry and juveniles

Abstract

This study determined the effectiveness of copper sulfate (CuSO4) to inhibit fungal growth (caused by Saprolegnia spp.) on largemouth bass (LMB) eggs spawned on/in fiber mats in very high‐alkalinity/‐hardness waters; experiments also determined the toxicity of CuSO4 to LMB fry and juveniles. An untreated control and three CuSO4 concentrations (10, 20, and 40 mg/L) were tested under a flow‐through scenario in the effectiveness experiment. Eggs were treated daily until hatching began. Fungal load at the time of hatch had a total area > 3.0 cm2 in the untreated controls, total area 1.0 to <2.0 cm2 in the 10 and 20 mg/L CuSO4 treatments, and total area > 1.0 cm2 in the 40 mg/L CuSO4 treatments. Fungus samples were identified as Saprolegnia australis. The 24‐hr median lethal concentration (LC50) values on the LMB yolk‐sac and swim‐up fry were 32.0 and 4.6 mg/L CuSO4, respectively; the No Observed Effect Concentrations (NOEC) were 16.0 and 0.125 mg/L CuSO4, respectively. Juvenile LMB were extremely tolerant to CuSO4, and their 24‐hr LC50 value was 185.5 mg/L; the NOEC was 64 mg/L. This study indicates that CuSO4 can be an important resource for hatcheries to control egg fungus, especially in high‐alkalinity/‐hardness waters.

Toxicity of Copper Sulfate to Largemouth Bass Fry in Naturally Soft Water

“…In the present study, the bioassay water was slightly opaque at the highest CuSO 4 concentration (20 mg/L); this can be attributed to Cu forming various carbonate complexes as described in Straus (2008). This slight cloudiness was present in our earlier study in higher alkalinity/hardness water with LMB (Straus et al 2020) at concentrations of 16 mg/L CuSO 4 and higher according to photos from that study, but this was not described in the publication.…”

“…fungus on incubating freshwater fish embryos and fish (Boyd and Tucker 2014); it has also been used to treat bacterial and parasite infestations of fish. As in Straus et al (2020),…”

“…Fungus control with CuSO 4 on embryos of Channel Catfish Ictalurus punctatus, sunshine bass (female White Bass Morone chrysops × male Striped Bass M. saxatilis), and LMB is extremely effective and economical for farmers in waters with moderate-or high-alkalinity/hardness (Straus et al 2009a(Straus et al , 2009b(Straus et al , 2011(Straus et al , 2012a(Straus et al , 2012b(Straus et al , 2016(Straus et al , 2020Mitchell et al 2010). It is well known that the toxicity of CuSO 4 decreases as pH and the concentrations of alkalinity, calcium hardness, and dissolved/particulate organic matter increase (Boyd and Tucker 2014).…”

“…Boyd et al (2016) comments that the BLM model is too complex for everyday use in aquaculture and recommends the practical treatment rate (as mg/ L CuSO 4 ) calculation of MacMillan (1985), which is calculated by dividing the total alkalinity by 100. Toxicity of CuSO 4 to Channel Catfish, sunshine bass, and LMB fry in moderate-or high-alkalinity/hardness waters has been studied previously (Straus 2008;Straus et al 2016Straus et al , 2020; in the Channel Catfish study, alkalinity and hardness was 217 and 126 mg/L, for sunshine bass it was 216 and 266 mg/L, and for LMB it was 384 and 452 mg/L, respectively. However, fry toxicity in low-alkalinity/hardness waters is still a concern in softer water hatcheries throughout the United States.…”

Characterizing the Mechanisms of Metalaxyl, Bronopol and Copper Sulfate against Saprolegnia parasitica Using Modern Transcriptomics

“…In addition, copper sulfate is effective in controlling the mycelium growth of largemouth bass eggs (caused by Sapproplegnia spp.) and improving fry survival in mat spawning [ 17 ].…”