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

Abstract

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 × 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.

Disinfection of teleost eggs: a review

“…A negative impact on hatching was only observed when the highest concentrations or contact times of a range of protocols were adopted (Kitancharoen et al . ; Small & Wolters ; Small & Chatakondi ; Verner‐Jeffreys et al . ; Can et al .…”

“…, , ,b, ; Small & Chatakondi ), twice a day (Barnes et al . ; Khodabandeh & Abtahi ), 3 or 4 times a day (Small & Chatakondi ), every other day (Bailey & Jeffrey ; Rach et al . ) or once a week (Wanatabe, ) depending on the study.…”

“…Fungal infections such as saprolegniasis can cause large‐scale problems in fish farms (Piper et al . ; Small & Chatakondi ). Fungal spores are ubiquitous in hatchery water supplies and are able to elicit large fungal outbreaks depending on the incubation time of the egg, the water temperature or organic load.…”

Evaluation of oxidative stress markers in the heart and liver of rainbow trout (Oncorhynchus mykiss walbaum) exposed to the formalin

“…Eggs treated three times daily with 100 ppm formalin had the highest ( p  < 0.05) percentage of hatched eggs (Small and Chatakondi 2006). Barnes and Soupir (2007) have recommended either daily 15-min formalin treatments at concentrations of at least 750 mg/L or every-other-day treatments at 1667 mg/L to adequately control fungus and maximize rainbow trout egg survival.…”

“…Small and Chatakondi (2006) have recommended three daily treatments of hybrid catfish (channel catfish Ictalurus punctatus  × blue catfish I. furcatus ) eggs with 100 ppm formalin as a 15-min bath. Eggs treated three times daily with 100 ppm formalin had the highest ( p  < 0.05) percentage of hatched eggs (Small and Chatakondi 2006).…”