CRABTRACKER,
Read this article it may answer your question on tagging small crabs,
Crab A lot!
DR. YONATHAN ZOHAR - University of Maryland, Center of Marine Biotechnology (COMB)
The Research: Merging Modern Biotech with Traditional Marine Science
Yonathan Zohar has spent decades working to overcome barriers in aquaculture that will enable increased production of marine finfish and blue crabs for food and for restocking declining wild stocks. In addition to this work, he is also the director of the University of Maryland's Center of Marine Biotechnology (COMB), which is housed in the Columbus Center, a unique building located directly on the harbor in Baltimore, Maryland's famous waterfront district.
According to Zohar, COMB strives to merge the tools of modern biology and biotechnology, including molecular genetic and genomics, with traditional marine science. The express goal for COMB is to study, protect, and enhance marine and estuarine resources, with a special focus on the Chesapeake Bay. That umbrella encompasses activities ranging from research, to education, to economic and business development. The Biotechnology Institute, of which COMB is a component, is in fact the only arm of the University of Maryland system charged with economic development.
The two main foci at COMB are fisheries and aquaculture biotechnology, and marine microbial biotechnology, with programs aimed at marine natural products discovery and development, marine environmental biotechnology, and emerging technologies.
- VIDEO CLIP 1: "The COMB Mission"
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Pushing Past Marine Finfish Aquaculture Bottlenecks
Zohar has spent over twenty years developing techniques to improve aquaculture production, specifically by working to eliminate bottlenecks such as spawning limitations and low larval survivorship rates.
One of the main questions Zohar's work has addressed is how to induce spawning in a variety of finfish species year round, even those species that initially would not spawn at all in captivity. Initial work in the area was focused on attempts at recreating environmental conditions to induce spawning, but with little success because fish in the wild are exposed to such a wide range of environmental cues that pinpointing those most critical was extremely challenging.
Zohar and his colleagues did, however, discover after years of work that because fish in tanks do not have the environmental conditions of their spawning grounds, they do not produce a certain small brain hormone that is essential for triggering spawning. Subsequently, the researchers were able to develop a highly potent, synthetic version of the hormone. They then incorporated this hormone analog into polymers that, once administered to fish, release hormone continuously to induce spawning at any time throughout the year. This technique is being used commercially with salmon and a variety of other species such as grouper and snook. Further research on the topic is being directed at creating the environmental conditions at aquaculture facilities that will induce natural production of the hormone, and searching for a relatively simple way to artificially turn on the genes that produce the brain hormone on so that synthetic hormone will not have to be injected in fish. The same brain hormone also plays a role in human reproduction, and Zohar's work in this area ultimately led also to advances in human reproductive physiology.
Once finfish are induced to spawn, the effort is of little use if too few of the larvae produced survive. Early in the development of finfish techniques, larval survivorship was in fact very poor. However, through careful study of nutritional requirements for larvae, specifically of enzymes normally produced by the larvae but not in captivity, Zohar and his colleagues were able to develop microencapsulated diets that provided the essential components required. These diets are now being used in the industry to enhance survival as well as growth of larval fish.
- VIDEO CLIP 2: "COMB Foci: Microbial Marine Products, Remediation, Aquaculture Technologies"
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The Blue Crab Project
The blue crab, Callinectes sapidus, is a Chesapeake Bay icon, but it is in danger of collapse because of a variety of problems such as pollution and overfishing. Zohar is part of an extensive ongoing multi-disciplinary, multi-institutional blue crab research project aimed at both better understanding the basic biology of the blue crab and using aquaculture hatchery technology to raise blue crabs that can be used to replenish ailing stocks in the Chesapeake Bay. "In view of the huge economic importance of the blue crab to the Chesapeake Bay, it's really surprising how little is known about the animal's basic biology," says Zohar.
In many ways, the major goals of the blue crab project have paralleled Zohar's work on finfish. The researchers have worked to identify hormones that regulate critical blue crab functions including molting and reproduction and have been able, for the first time, to 'close' the life cycle of the blue crab by inducing spawning and raising resulting larvae to reproductive age, then inducing spawning again.
The blue crab has a complex life cycle with nine different larval stages before metamorphosis into the form most people recognize. Again, extensive research was done to identify enzymes essential to growth, in this case for each of the multiple larval stages. This led to an understanding of critical enzymes that could be supplied in feed to support healthy larval growth.
- VIDEO CLIP 3: "The Blue Crab Project"
- VIDEO CLIP 4: "The Maryland Aquaculture Industry Connection"
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Setting them Free
Another critical aspect of the blue crab project has been determining how best to monitor released juveniles to determine if in fact hatchery-raised crabs could increase the wild blue crab population and blue crab catches. Releases of blue crabs raised at COMB are being conducted and monitored by partner institutions the Smithsonian, in Washington, D.C., and the Virginia Institute of Marine Science, in Gloucester Point, Va. Initial stages of this work required attachment of tiny coded wire tags to each of over 100,000 juvenile crabs released, making it the largest monitored release of any crustacean in the world. For the most part, released crabs are monitored through capture of samples by the research group to identify those with the tags, which typically last a few months until the crabs reach maturity. Such collections have led to a very good understanding of the survivorship of the released crabs and also their general whereabouts. "The results look really good," says Zohar, "it looks like this concept can work." The idea is that the released crabs, which have not been genetically altered in any way, can integrate with natural blue crab breeding stocks. Each successfully integrated crab can contribute millions of eggs to the Chesapeake Bay, where wild breeding stocks have declined by about 80% in past decades.
The ultimate goal is to release juveniles by the millions but still monitor integration with the wild population, meaning that wire tags will be an untenable option. Zohar and colleagues are therefore developing a genetic test for released juveniles. The idea is to identify genetic markers in the brood stock at their hatching facility. Then, as crabs are harvested in the months and years following releases, they can be tested for these markers to determine if they were released animals or their offspring. Large numbers of crabs with these markers harvested would be a strong sign of success for the program.
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When Crabs Attack
One of many hurdles that researchers have addressed in the blue crab project is the problem of captive crabs attacking each other. This result had in the past prevented groups from being able to successfully culture blue crabs. The team has worked around this problem using a number of methods. One was to provide enough room for the crabs to hide from each other and to provide them plastic nets that offer adequate shelter for hiding. To reduce cannibalism, they simply learned the level of feed required to keep everyone full, asÑhappily for the projectÑsatiated crabs tend to not eat one another. The group is also looking for more sophisticated solutions to the cannibalism problem as well. Zohar says the researchers are working to zero in on genes and hormones responsible for aggression and cannibalism so that these factors can be controlled. The researchers also hope to identify and understand the genes that control molting. This might allow them to trigger all animals in a given tank to molt at the same time, eliminating the problem of crabs with their shells attacking nearly defenseless crabs that have recently molted.
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Education: An OB/Gyn for Fish
"As a kid, I was always fascinated by the marine environment and marine life," says Zohar, so naturally when it came time to go to college, he chose a path in marine science. Zohar, who is originally from Israel, did both his undergraduate in biology and masters in oceanography at the Hebrew University of Jerusalem. He became interested in aquaculture and mariculture while working on his master's because of a developing interest in marine environmental conservation. For his Ph.D., Zohar moved to France, where he attended the University of Paris. There he began in earnest to study fish reproduction and got his degree in comparative endocrinology and marine biology. Afterward, he returned to Israel and worked for ten years in the Israel National Center for Mariculture and Marine Aquaculture on the Red Sea. In 1991 he moved to the U.S. and joined COMB. He became director in 1997. Zohar says, "Sometimes I tell people that what I do is really like an OB/Gyn, but just in fish."
- VIDEO CLIP 5: "The Zohar Aquaculture Connection"
- VIDEO CLIP 6: "Biotech Solutions to Oyster Fisheries Diseases?"
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