Abstract
To evaluate the effects of water hardness on survival to hatch of eyed rainbow trout Oncorhynchus mykiss eggs during iodophor disinfection, hard (300 mg/L CaCl2) and soft water (20 mg/L CaCl2) solutions were used in combination with iodophor treatments of 0, 100, 200, 400, 800, and 1600 mg/L. Water hardness did not significantly influence egg survival-to-hatch. In addition, there was no significant interaction between water hardness and iodine concentration on egg survival. However, significant differences in egg survival due to iodine concentration were observed. Egg survival significantly decreased at 800 mg/L, with near complete mortality occurring at 1,600 mg/L. Rainbow trout eyed egg disinfection using iodine concentrations of 800 mg/L or greater are not recommended, regardless of water hardness (calcium) concentrations. Keywords: Eyed eggs, iodophor, disinfection, rainbow trout, water hardness, mortality.
Highlights
Fish eggs are chemically disinfected to reduce the risk of introducing pathogens into fish hatcheries (McFadden, 1969; Amend and Pietsch, 1972; Piper et al, 1982; De Swaef et al, 2015)
Povidone has been listed as a Low Regulatory Priority drug by the U.S Food and Drug Administration, allowing it to be used at a concentration of 100 mg/L active iodine for 10 min on fish eggs (United States Food and Drug Administration, 2021)
Water hardness had no significant (P > 0.05) effect on egg survival at the different iodine concentrations used during egg disinfection (Figure 1; F = 0.34, P = 0.57)
Summary
Fish eggs are chemically disinfected to reduce the risk of introducing pathogens into fish hatcheries (McFadden, 1969; Amend and Pietsch, 1972; Piper et al, 1982; De Swaef et al, 2015). Povidone has been listed as a Low Regulatory Priority drug by the U.S Food and Drug Administration, allowing it to be used at a concentration of 100 mg/L active iodine for 10 min on fish eggs (United States Food and Drug Administration, 2021). This treatment is effective in reducing, but not eliminating, all bacteria on the external egg membrane (Kumagai et al, 1998; Wagner et al, 2008; Barnes et al, 2009). Iodine toxicity and efficacy are not generally affected by overall water chemistry (Backer and Hollowell, 2000; Fraise et al, 2004), it is possible that specific chemical components of the water used to create the treatment solutions may impact subsequent egg survival
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