Now that the spawning season is approaching, how did your hatching go last year? Did you obtain satisfactory hatching rates? If not, it would be good to consider making some changes in the hatchery.
Disinfecting eggs daily to improve hatch by reducing fungus and bacterial infections is a recommended practice. Research has shown that a number of compounds are effective disinfectants, but farmers are restricted to those chemicals in the FDA approved or “low regulatory priority” categories: povidone iodine, formalin (approved brands) and hydrogen peroxide.
Iodine is commonly used as a dip for eggs before they are placed in troughs. Formalin is effective (Rach et al. 1997) but produces a strong smelling noxious gas. OSHA recommends handled formalin in the workplace as a potential occupational carcinogen (Lee and Radtke 1998) with protective gear required during handling. Hydrogen peroxide, H2O2, is an attractive alternative because it is odorless and breaks down into oxygen and water. A 3 percent hydrogen peroxide solution is widely used in homes for treatment of minor wounds or as a gargle. It is also relatively inexpensive. Stock solutions come as 35 - 50 percent hydrogen peroxide, and adequate care must be taken in handling and storage. Stock hydrogen peroxide is a strong oxidizer. It will burn you, on contact! Protective gear is required. See the label and MSDS sheet.
Research by Brian Small of the ARS Catfish Genetics Research Unit, Thad Cochran National Warmwater Aquaculture Center (Small 2002, Small and Wolters 2003) has shown that daily 15-minute baths of hydrogen
peroxide at a rate of 250 ppm are effective at improving the hatching success of channel catfish eggs. Alternatively, hydrogen peroxide can be added all-at-once to in-flow end of the hatching troughs, as a flowthrough treatment, at 70 ppm. Rach et al. (2004) found that a 15 minute flow-through treatment of hydrogen peroxide at 500 to 750 ppm was effective for controlling fungus on catfish eggs. This was true whether the eggs were still within the gelatinous matrix or sodium sulfite-treated. Water temperature during the study was 79 to 84°F (26 to 29°C).
Before treating with hydrogen peroxide, it is critical to consider two important factors: water temperature and exposure time. Hydrogen peroxide is more toxic at higher temperatures and a lower rate should be used (Rach et al. 1997, Small 2004). Even a minor temperature change makes a big difference. Small found that hatching success at 75°F (24°C) was greatest when eggs were treated with 250 - 500 ppm hydrogen peroxide (15-minute bath). At 82.4°F (28°C), hatching success was best at 100 to 250 ppm. At this higher temperature, the hatching rate decreased for eggs treated with 500 ppm. The toxicity of hydrogen peroxide is also greater at longer exposure times, so be sure to respect the time limits on the bath treatments. Before adopting a hatchery-wide program, first test hydrogen peroxide on small batches of eggs to determine a suitable concentration of hydrogen peroxide for your particular hatchery's conditions (Small 2004).
Previous work (Rach et al. 1998) on hydrogen peroxide for egg treatments was done in cooler water. Channel catfish were treated at 72°F (22 ± 2°C), lake sturgeon, paddlefish and common carp at 63°F (17 ± 2°C), and northern pike, walleye yellow perch and white sucker eggs at 54°F (12 ± 2°C). Mean hatch for eggs of a variety of fish species was greatest when treated daily for 15 minutes at 1,000 ppm.
Hydrogen peroxide can also be used to treat baitfish eggs during jar hatching. No formal studies have been done on eggs of these species as yet. Based on the typical range of incubation temperatures for golden shiner and goldfish eggs, an effective and safe rate is probably 1,000 ppm (at 65°F) and 250 ppm (at 75°F). Because baitfish eggs are only about 1 mm in diameter, hydrogen peroxide treatment will cause some eggs to float, buoyed by the temporary attachment of small bubbles. Jars must have a fine screen installed, of less than 1,000 microns, or eggs will be lost from the hatching jar.
Factors other than disease can result in poor hatch. Low dissolved oxygen or high ammonia levels are sometimes the cause. Mechanical shock and temperature shock can kill eggs as well, so eggs must be treated with care (like the babies they are) on the way to the hatchery.
Lee, S., and T. Radtke. 1998. Exposure to formaldehyde among fish hatchery workers. Case Studies. Dawn Tharr, Column Editor. Applied Occupational Environmental Hygiene 13(1):3-6.
Rach, J. J., G. E. Howe, and T. M. Schreier. 1997. Safety of formalin treatments on warmand coolwater fish eggs. Aquaculture 149:183-191.
Rach, J. J., T. M. Schreier, G. E. Howe, and S. D. Redman. 1997. Effect of species, life stage, and water temperature on the toxicity of hydrogen peroxide to fish. Progressive Fish-Culturist 59:41-46.
Rach, J. J., M. P. Gaikowski, G. E. Howe, and T. M. Schreier. 1998. Evaluation of the toxicity and efficacy of hydrogen peroxide treatments on eggs of war- and coolwater fishes. Aquaculture 165:11-25.
Rach, J. J., J. T. Valentine, T. M. Schreir, M. P. Gaikowski, and T. G. Crawford. 2004. Efficacy of hydrogen peroxide to control saprolegniasis on channel catfish (Ictalurus punctatus) eggs. Aquaculture 238:135-142.
Small, B. 2002. Treating channel catfish eggs with hydrogen peroxide can improve hatching success. Thad Cochran NWAC News, 5(2):6-7.
Small, B., and W. R. Wolters. 2003. Hydrogen peroxide treatment during egg incubation improves channel catfish hatching success. North American Journal of Aquaculture 65:314-317.
Small, B. 2004. Accounting for water temperature during hydrogen peroxide treatment of channel catfish eggs. North American Journal of Aquaculture 66:162-164.
By Nathan Stone, Extension Fisheries Specialist
Arkansas Aquafarming newsletter
University of Arkansas Cooperative Extension Program