There are hundreds of crab species, but only a few are commercially important.

UAB biologist Doug Watson, left, and graduate assistant Hsiang-Yin Chen say the team is close to discovering the structure of the molt-inhibiting hormone that could lead them to develop methods to induce molting on command to produce soft-shell crab as needed.

The states of Alabama, Florida, Mississippi, Louisiana and Texas brought in a blue crab bounty worth a total of $45.8 million in 2007, according to the National Marine Fisheries Service.

If there were a way to regulate the molting of blue crabs — which produces freshly molted, soft-shell crab considered a delicacy by many — then seafood consumers could enjoy them year-round, not just in late spring and early summer when they molt naturally.

It also could mean hundreds or thousands of new jobs along the Gulf and Atlantic coasts.

Unprecedented success
UAB biologist and researcher Doug Watson, Ph.D., is unraveling the process by which blue crabs molt, and says his team is close to discovering the structure of the molt-inhibiting hormone (MIH) receptor, which could lead them to develop methods to induce molting on command to produce soft-shell crab as needed. Molting is the process by which the crab discards its exoskeleton, replacing it with a temporarily soft, pliable new exoskeleton.

“No one yet has isolated or characterized this MIH receptor for any crustacean, but we think we have isolated a gene that codes for that receptor,” Watson says. “We’re not 100 percent sure yet, but the gene we have cloned has all the characteristics of the MIH receptor. We’re trying to determine for sure if it is.”

The identification and characterization of the MIH receptor would constitute a significant contribution to the field of invertebrate endocrinology.

“That’s the basic science and a key to answering the question of how growth and development are regulated in this group of organisms with so much ecological and economical importance,” Watson says.

Applied economics
The study is part of a two-year grant funded by the Mississippi-Alabama Sea Grant Consortium and a pilot grant from the Center for Biophysical Sciences and Engineering at UAB. Watson and his colleagues Teruaki Nakatsuji, Junying Zheng and current graduate students Hsiang-Yin Chen and Anna Pendleton are in year two of their research.

The applied science here is intervention by researchers to block the receptor that prevents molting.
Conceivably, then the growth of the animals could be controlled, and this could create jobs and stimulate local economies through private aquaculture or farming operations across every state touching the ocean — from Texas to Maryland, Watson says.

“It probably would have to take place in an aquaculture setting because it would be difficult to control in the wild,” Watson says. “Once they molt in the wild they are very vulnerable to predators because their shell is so soft.”

How would it work?
Watson says they will either need to develop an injection or food pellet that could be used to induce the molting process.

“Ideally, I think we’d like to work out a system in which the inducer is put in a food pellet and we could just feed it to them,” Watson says. “That’s a goal down the line. Right now we think we have the receptor, and we’ve developed a receptor blocker. We’re at a stage where we can test that. If it works, then we’ll worry about delivery.”

That process would be easier, more lucrative and less time-consuming for the producers of blue crabs than their current arrangement.

“The way soft-shell blue crabs are collected now is very labor-intensive, and it’s usually mom-and-pop organizations trying to do it,” Watson says. “They collect the crabs when they are ready to molt and then watch them every couple of hours 24 hours a day to see if the crab is molting. If we can control the molting, things can be timed in a much more manageable way. You could induce the molting and come back a specific period of time later and have soft-shelled crabs.”
Watson says watching a crab undergo the molting process is a remarkable sight.

“When you see it, I don’t know how you cannot be impressed,” he says. “It’s astounding that a complete new animal crawls out of that exoskeleton — and it’s much bigger. The new exoskeleton, once hardened, can accommodate additional growth of soft-tissues like muscles and internal organs. The process of molting is a sight to behold.”