Use of copper sulfate and peracetic acid as therapeutants on fish: can these replace formalin?

Authors: Straus, David - Dave; MEINELT, THOMAS - Leibniz Institute Of Freshwater Ecology And Inland Fisheries

Submitted to: Aquaculture Europe 2016 - Book of Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/4/2016
Publication Date: 9/21/2016
Citation: Straus, D.L., Meinelt, T. 2016. Use of copper sulfate and peracetic acid as therapeutants on fish: can these replace formalin? [abstract]. Aquaculture Europe 2016 - Book of Abstracts. p. 986-987.

Interpretive Summary:

Technical Abstract: Copper sulfate (CuSO4) and peracetic acid (PAA) are compounds that have been found to be useful in several areas of aquaculture around the world. In the United States, CuSO4 is used for treatment of an ectoparasite (Ichthyophthirius multifiliis) on fish (Straus 1993; Tieman and Goodwin 2001), and saprolegniasis, or water-mold, on fish eggs (Straus et al. 2009; Straus et al. 2016); research with PAA has shown it is also effective for saprolegniasis on fish eggs (Straus et al. 2012). There is interest in using it as a general disinfectant at aquaculture facilities. In Europe, use of CuSO4 is minimal due to environmental safety concerns, although there are several instances where it is used for saprolegniasis on juvenile or adult fish; interest in the various uses of PAA as an egg disinfectant, to treat fish saprolegniasis, and as a water treatment in recirculating aquaculture systems (RAS) is widespread. Here we will discuss research to treat saprolegniasis on fish eggs. Formalin is a known carcinogen. Several European countries restrict the use of formaldehyde, and the European Union banned the use of formaldehyde due to its carcinogenic properties in certain antifouling applications (NICNAS 2013). So, can CuSO4 and/or PAA be possible replacements for use of formalin as a therapeutant in aquaculture? Materials and methods Sunshine bass eggs were treated with tannic acid to remove adhesiveness and then with iodine to disinfect the eggs as in a typical hatchery; the approximately 1 mm eggs were counted with an optoelectronic XperCount™ enumerator (Masson et al. 2013) and transferred to each hatching chamber of our experimental system. Eggs were exposed to three CuSO4 concentrations (10, 20, and 40 mg/L) and an untreated control (n=3). Water flow maintained the rolling action of the eggs per industry standards. Because eggs start hatching after 2 d, treatment began immediately the afternoon of spawning with a 10 min aerated, static bath and was repeated morning and afternoon on Day 2. Eggs were not treated after hatching began. The resulting fry were counted on Day 4 with the XperCount™ to determine percent survival for each treatment. Channel catfish eggs (approximately 4 mm) were used in the PAA study and consisted of five concentrations (2.5, 5, 10, 15 and 20 mg/L) and an untreated control in a flow-through system. A single spawn was used for each replication (n=4). Eggs were treated twice daily until the embryos developed eyes (5 days). When hatching was complete (9 days), fry were counted to determine percent survival for each treatment. Results With CuSO4, saprolegniasis was severe in the untreated controls (28% survival). Very little water-mold was present in treatments receiving 10 mg/L (32% survival) or higher. The best survival was at 40 mg/L (50% survival); however, the 20 mg/L CuSO4 treatment (46% survival) gave similar results and allows for a greater margin of safety. We developed an in vitro assay that confirmed maximum saprolegniasis inhibition was achieved at 20 mg/L CuSO4. For PAA, fungal growth was severe in the untreated controls (11% survival). The highest percent survival of hatched fry was 5 mg/L (63%) administered twice daily. The 2.5 mg/L treatment had slightly less survival (60%), but provides a higher margin of safety to the eggs. The 10 mg/L treatment resulted in comparable survival (62%), but the margin of safety would be smaller and it is not recommended. Very little water-mold was present in treatments receiving 2.5 mg/L or higher, and concentrations of 15 and 20 mg/L PAA were toxic to the eggs. Discussion and conclusion These results demonstrate that 20 mg/L CuSO44 and 2.5 mg/L PAA controlled saprolegniasis on sunshine bass and channel catfish eggs, respectively. Results from the CuSO4 study demonstrate the effectiveness of controlling saprolegniasis and increasing sunshine