OXYGEN REQUIREMENTS OF SEPARATED HYBRID CATFISH ? Ictalurus punctatus × ? I. furcatus EGGS.

Channel catfish Ictalurus punctatus egg masses require ambient water with over 95% air saturation to maintain maximum oxygen consumption as they near hatch. Since hybrid catfish eggs (channel catfish ♀ X blue catfish I. furcatus ♂) are often kept separated after fertilization by the addition of fuller's earth and incubated in large tube incubators, it is assumed that the critical oxygen requirement is lower. This study was conducted to determine the recommended dissolved oxygen concentration for incubation of hybrid catfish eggs.

A 300 ml Wharton BOD bottle with a Hach LED oxygen sensor was used as the respirometer. A 2" magnetic spin bar was placed in the bottle and used to mix water throughout the chamber and suspend the loose egg/sac fry sample. The bottle was placed in a water bath at 24.8°C on a stir plate and the rotational speed adjusted to the minimum required to suspend the eggs in the bottle (60-90 RPM). The exact time of fertilization was noted for each spawn as the eggs were fertilized and placed in separate McDonald jars to incubate. The age (hours post-fertilization) was noted when each egg or fry sample was tested. A 15-45 gram egg or fry sample was siphoned from each of several McDonald jars daily through the incubation period and three days post-hatch.

DO and temperature were measured and recorded every 1-5 minutes (more frequent measurements with older eggs having a higher metabolic rate) for 1-4 hours. A total of 51 measurements were made on 16 different spawns at 1-5 days post-fertilization, and a total of nine measurements were made on sac fry from five different spawns ranging in age from 0-2 days post-hatch.

The maximum DO required by hybrid catfish eggs increased throughout the incubation period, peaking at 79% air saturation during the last two days of incubation. Sac fry required approximately 55% saturation for the first two days post-hatch. Hatchery managers should maintain DO above 80% during the last two days of incubation.