2009 Annual Report
1a.Objectives (from AD-416)
The objective of this cooperative research project is to test and further develop a novel incubator for use in commercial channel catfish hatcheries.
1b.Approach (from AD-416)
Catfish incubators have been largely unimproved since first developed in 1929. Egg masses are held in baskets made with ¼” mesh hardware cloth. Paddles held on a rotating shaft turn through the water between baskets, moving water through the baskets, aerating the eggs. As the eggs hatch, the sac fry pass through the mesh of the basket and sink to the bottom of the trough, where they are siphoned up. Farmers often experience problems (fungus and/or bacteria on eggs, resulting in poor hatch rates) during the peak of the spawning season when hatchery space is limited and egg masses are often crowded in the baskets at higher than desired densities. Recent research conducted by ARS has demonstrated that the oxygen requirements of catfish egg masses are higher than previously thought. This research has led to a preliminary design for a new hatchery system.
Sixteen standard hatchery troughs were equipped with the See-Saw incubation system. Due to the late approval of the project, most of this first season was used to design the system, purchase motors and material for fabrication of the supports, racks, and hatching baskets, and preliminary stress-testing of the system without live eggs. Near the end of the spawning season the first comparative trial was conducted. Pairs of troughs (one control and one test) were sequentially loaded with eggs. See-Saw and control troughs (n=4 of each) were loaded with 25.6 ± 0.5 egg masses per trough (474,947 ± 3002 and 472,878 ± 3892 eggs per trough, respectively). This is 2.0 - 1.5x higher than recommended loading rates. Water quality (water flow, dissolved oxygen (DO), pH, total ammonia nitrogen, and nitrite nitrogen) were measured in the water supply and in each trough daily. When the eggs hatched, sac fry were measured volumetrically and sub-sampled to determine total number, then transferred to rearing troughs. When the fry reached swim-up stage, they were measured volumetrically and sub-sampled to determine total number before transfer to rearing ponds. Our intent was to determine both hatch rate (live sac fry recovered as a percentage of eggs initially stocked) and survival to swim-up. However, when the sac fry were transferred, a significant portion of those from the control troughs were dead. We presume that they died prior to hatching from anoxia in the interior of the spawns and the egg shells later ruptured. Since we were not able to easily separate living from dead sac fry, we were not able to determine hatch rate, although we do presume that it was higher in the See-Saw. We plan to utilize a micro-fluorescent oxygen sensor in Year 2 so actual DO concentrations in the egg mass interiors can be determined under a variety of egg loading rates and ambient DO concentrations. We also noted that eggs in the See-Saw took approximately one additional day to hatch. It has been previously shown that eggs subjected to low oxygen stress will hatch prematurely and with a poorer hatch rate so this was not unexpected. Survival to swim-up stage was significantly higher in the See-Saw than the traditional control troughs. Survival to swim-up stage averaged 53.6 ± 7.1% in the See-Saw, versus 23.3 ± 6.5% for the control troughs, a 2.3-fold difference. While survival in the See-Saw was lower than expected, that was attributed to the generally poor egg quality from eggs collected at the end of the season. The ADODR monitors this project through site visits, telecoms and e-mails to the collaborator, and through annual reports from the collaborator.