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March 2003, Vol. 12, No.3 | Return to Table of Contents
Cod Reproduction Focus of MBL Study
 Scientists at the Marine Biological Laboratory recently launched a project aimed at learning more about the reproductive biology of Atlantic cod. They ultimately hope to develop techniques to store unfertilized cod eggs, and to provide cod broodstock (fish held for reproduction) and eggs that are free of nodavirus, a pathogen causing significant mortality in farm-raised cod in North America. Interest in cod aquaculture has increased steadily since the1980s and 1990s as cod fisheries declined to unprecedented levels.
The project is led by Dr. Rick Goetz, a Senior Scientist in the MBL’s Marine Resources Center (MRC). Goetz also directs the Center’s Program in Scientific Aquaculture. In October, Goetz transported several mature cod to Woods Hole from a fishing vessel out of Chatham, Massachusetts. In mid-November, about 30 additional cod broodstock were obtained and brought back to the MBL. Before being brought into the four-feet deep MRC tanks, however, the fish first had to be treated for pressure disorders.
Cod live at depths from 100 to 200 feet. Like scuba divers moving too quickly between different water levels, cod are sensitive to changes in water pressure. To ensure that the cod they collected were properly equilibrated, Goetz and his colleagues held the fish in cages off the MBL and WHOI docks, where the water is between 60 and 80 feet deep. After bringing the fish up to increasingly shallower depths over a 24-hour period, the cod were then able to be transported to the shallow MRC tanks.
A single female cod can reproduce as many as 20 times during a reproductive season. During the Fall, the cod broodstock held at the MRC spawned throughout November and part of December. While cod eggs normally exhibit optimal quality for only a short time after ovulation, Goetz is working to develop a way of holding ovulated cod eggs in a viable condition outside of the female for as long as possible. In addition, researchers in the Goetz lab have developed an extremely sensitive molecular based assay for the rapid detection of nodavirus. The objective is to use the assay to screen for the virus in cod broodstock prior to spawning. Because the virus may be transmitted from the adult to the eggs, the assay could be used to screen out carriers of the virus so that only cod that are free of nodavirus are produced.
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