Location: Warmwater Aquaculture Research UnitTitle: Oxygen requirement of separated hybrid catfish eggs
Submitted to: NWAC (National Warmwater Aquaculture Center) Aquaculture Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: 11/15/2017
Publication Date: 12/6/2017
Citation: Torrans, E.L., Ott, B.D. 2017. Oxygen requirement of separated hybrid catfish eggs. NWAC (National Warmwater Aquaculture Center) Aquaculture Newsletter. 14(1):8-9.
Interpretive Summary: t has previously been determined that channel catfish egg masses require water near air-saturation with oxygen to avoid any negative effect of oxygen stress. The necessary oxygen concentration for hybrid catfish eggs, which are incubated as loose eggs in large tube incubators, has not yet been determined. This study determined that loose hybrid catfish eggs require water only 80% saturated with oxygen during the last day of incubation.
Technical Abstract: Channel catfish egg masses require hatchery water with over 7.8 ppm dissolved oxygen at 80° F (95% air saturation) to maintain maximum oxygen consumption as they near hatching. This concentration is called the critical oxygen requirement by scientists but for the purpose of this article we will call it the oxygen requirement or required oxygen. With a lower oxygen concentration, the developing embryos consume less oxygen, hatch prematurely, and have a poorer survival. Premature hatching has also been linked to the so-called “triple-tail” deformity. Hybrid catfish eggs (female channel catfish X male blue catfish) are rarely produced by natural pond spawning but usually by “hand-stripping” in the hatchery after the female receives a series of hormone injections. Hybrid eggs are often kept separated after fertilization by the addition of fuller’s earth and are incubated in large tube incubators (Figure 1). It is assumed but not known that the oxygen requirement for these separated hybrid catfish eggs is lower than for channel catfish eggs contained in an entire spawn. This study was conducted to determine the oxygen requirement for incubation of hybrid catfish eggs. A total of 43 measurements were made on 16 different spawns at 3-5 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 (Figure 2). The water temperature over this period averaged 77° F. The dissolved oxygen required by hybrid catfish eggs increased throughout the incubation period, peaking at 6.5 ppm (79% air saturation) during the last two days of incubation. This is considerably lower than the oxygen required by catfish eggs in an intact spawn. While sac fry have a higher metabolic rate (greater oxygen consumption per body weight) than hybrid embryos just before hatching, the loss of the egg shell makes oxygen transfer easier, and sac fry only require approximately 4.5 mg/l of dissolved oxygen (55% saturation) for the first two days post-hatch. Hatchery managers should maintain DO at or above 6.5 ppm during the last two days before the eggs hatch.