Efficacy of Formalin as an Egg Disinfectant for Improving Hybrid Catfish (Channel Catfish × Blue Catfish) Hatching Success

—Formalin is currently the only aquaculture drug approved by the U.S. Food and Drug Administration for the control of fungi on the eggs of all finfish. The efficacy of formalin for disinfecting hybrid catfish (channel catfish Ictalurus punctatus 3 blue catfish I. furcatus) eggs was examined and compared with that of three other potential chemotherapeutants. Two experiments were conducted to evaluate treatment dose and frequency on the hatching success of the hybrid catfish. In the first experiment, hybrid catfish egg masses were divided and assigned to 1 of 13 treatments administered as daily 15-min baths. The treatments were as follows: (1) control (no treatment), (2) 50 ppm (mg/L) formalin (F), (3) 100 ppm F, (4) 200 ppm F, (5) 125 ppm hydrogen peroxide (HP), (6) 250 ppm HP, (7) 500 ppm HP, (8) 50 ppm povidone iodine (PI), (9) 100 ppm PI, (10) 200 ppm PI, (11) 2.5 ppm copper sulfate (CS), (12) 5 ppm CS, and (13) 10 ppm CS. Hatching success tended to be highest among eggs treated with 100 ppm F (87.7%), 2.5 ppm CS (87.0%), or 100 ppm PI (85.2%), although these success rates were not significantly (P . 0.05) different from that in the control treatment (82.8%). Treatment with 500 ppm HP resulted in a significant (P , 0.05) decrease in hatching success (31.5%). In the second experiment, the optimal frequency of formalin treatments was assessed by treating hybrid catfish eggs zero, two, three, or four times daily. Eggs treated three times daily with 100 ppm F had the highest (P , 0.05) percentage of hatched eggs. To maximize hatching success, three daily treatments of hybrid catfish eggs with 100 ppm F as a 15-min bath is recommended. Fungal and bacterial egg infections can be a significant problem in commercial catfish hatcheries. Dead eggs and other organic matter in hatchery culture systems provide excellent substrates for these pathogens. Without chemotherapeutic treatment, these pathogens can quickly overtake the egg mass and significantly reduce embryo survival * Corresponding author: [email protected] Received February 18, 2005; accepted June 9, 2005 Published online November 23, 2005 and hatching success. Several chemical therapeutants have been investigated as potential treatments to control fish egg diseases. Currently, formalin is the only chemotherapeutant designated by the U.S. Food and Drug Administration (FDA) as an approved aquaculture drug for treating all finfish eggs; however, other potential chemotherapeutants are being investigated. Among those chemotherapeutants under investigation, hydrogen peroxide, povidone iodine, and copper sulfate have been suggested as alternatives to reduce channel catfish Ictalurus punctatus egg infections and thus improve hatching success (Walser and Phelps 1993; Rach et al. 1998, 2004; Small and Wolters 2003; Small 2004; B. R. Griffen, Harry K. Dupree–Stuttgart National Aquaculture Research Center, unpublished data). Hydrogen peroxide and povidone iodine are currently designated by the FDA as Low Regulatory Priority aquaculture drugs when used as egg surface disinfectants, and the use of copper sulfate is currently under an Investigational New Animal Drug exemption