Even adult fish do not select and "taste" food the way we do, with our tongues. Instead, fish have epibranchial organs that sense the chemical makeup of food. "A fish sucks something into its mouth and stuffs it into the epibranchial organ," says Rittschof. "If it tastes good, the fish swallows it. If it doesn't, it spits it out." Preferred foods share certain chemical traits - complex combinations of molecules that fish find "tasty."

Fish food used in aquaculture is often based on cereal, which lacks the flavor molecules that fish prefer. "Cereal doesn't taste like a hamburger," Rittschof says. "Vegetarians know that." The researchers' first hurdle was to find a flavoring that adult fish preferred - and they found that soup stock was a favorite with a wide range of fish, including salmon, trout, flounder and bass.

The second hurdle was to convince larval fish to eat a processed food. Fish are visual predators who expect their food to move, and baby fish usually eat microscopic creatures like rotifers or brine shrimp. Even adult fish must be trained to accept fish pellets as food, and no one was sure that baby fish could learn to recognize motionless fish flakes as something edible.

In Rittschof and Bonaventura's experiment, they fed baby flounder through pipettes - first with brine shrimp and later with manufactured liposomes full of the nutrients they needed. The lipids in the liposomes' walls prevented the food from dissolving in water. And the researchers found that the larval fish would eat the processed food. "Baby flounder are very smart," Rittschof says. "They'll sit at the end of the pipette and wait for food." He remembers this more than anything else about the experiment, though his findings led to the large-scale production of flavored fish food and the development of chemically attractive fishing lures.

His appreciation for the miniscule flounder, and for the way they adapt to their environment, reflects his boundless curiosity about animals, their habitats and the surprises they offer. This curiosity makes him a perfect match for Duke Marine Lab, which is situated in Beaufort amid estuaries and barrier islands and which celebrates the importance of a sense of place.

"Dan embodies one of the primary principles of the lab, which is that it is a field station," says Mike Orbach, director of the marine lab. "People can get out and get dirty, literally, and see nature in all its cycles." Orbach says Rittschof is one of the most active faculty members, as far as getting students involved with field research. "He's a denizen of Carteret County waters - he knows where everything is all the time." One reason for this knowledge is that Rittschof spends day and night at the marine lab, exposing students to the natural world that surrounds Pivers Island. He leads countless field trips. He keeps his laboratory and office open for student projects, and students have used his printer to spool off reams of research papers.

From his third-floor office, Rittschof can look across a narrow channel and see one particular estuary - "his" estuary - a square kilometer of sand, mudflats and shallow water on Carrot Island. For the last 17 years, he has been getting intimately aquainted with his estuary, fascinated by the vital interconnectedness of its parts.

Terns and killdeer sweep across the embayment, island horses wade through it, flounder skim along its bottom. Fresh water seeps in from a spring on the eastern shore. On very high tides, ocean water spills across the dunes to flood the bay with salt. Every inch of the estuary offers new research possibilities.

"All the male blue crabs sit in pits in one tiny part," Rittschof says. "Are they there because of physics or does it smell good to them?" Though the bottom of the estuary is crowded with thousands of tiny snails, some patches are completely bare. Why? For Rittschof and his students, the estuary is an open-air laboratory that provokes an endless stream of questions. He leads nighttime canoe trips there, catches its flounder by hand, tracks its snails and sediments, measures its salinity. With Jonathan Kool, a graduate student, he is mapping the estuary in 10-meter increments and digitizing all its flora and fauna, its sediments and waters, using the Geographic Information System (GIS).

"I want to know how everything works in this soft-bottom environment," he says. "I'm doing this because I'm curious about it and I like it. I want to know how the world is put together." Rittschof hopes to make a long-term database of all the activity in the estuary to document and publicize the animals' interactions with each other and with the environment.

The estuary project is merely the latest and most ambitious in a line of research projects that stretch back to Rittschof's childhood. He has made a career of asking "why." As a boy, he spent summers in northern Michigan with his family. "When I wasn't picking cherries for money, I was catching things," he says. "Usually I was fishing. I was interested in anything that moved." He was especially intrigued by the creatures that crept and slithered and flew at night. Nightcrawlers were a favorite catch.

"And then I caught things for my dissertation," he says. "Frogs." Though his favorite high-school subject was chemistry, he found himself drawn to ecology at the University of Michigan. His college studies saw the beginning of his exploration of the interrelationships between animals and their environment, and for his doctoral dissertation, he studied the chemical ecology of hibernating freshwater frogs. Then came a turning point. Just after receiving his Ph.D. in 1975, Rittschof saw the ocean for the first time, on a trip to the Florida Keys. A child of the Southwest and Great Lakes regions - he was born in Arizona in 1946 - Rittschof had never seen the marine environment face-to-face. And now he was sure of one thing: he wanted to study chemical ecology in marine systems.

After post-doctoral work in biochemistry at the University of California at Riverside, Rittschof got his first chance to tackle a real-life problem. One of his Michigan professors had questioned the mechanisms by which hermit crabs in the Gulf of Mexico locate new snail shells to live in. Hermit crabs have no hard covering of their own, and as they grow, must constantly find larger snail shells to inhabit. How do they find empty shells of the correct size?

Rittschof believed that the answer lay in the crabs' ability to detect certain chemicals that were released when the snails died. "Chemical perception is a sense that you don't think about much," he says. "It's much more than the sense of taste or the sense of smell. There are additional capabilities, like pheromone reception and the perception of environmental odors, that are poorly understood."

To support his theory, Rittschof had to locate the specific molecule that the crabs responded to, and figure out how it was produced. Working on vacation and during the afternoons at a Florida conference, he researched and wrote two papers that described his discovery: when one snail eats another, an enzyme in its saliva reacts with the other snail's muscle tissue to produce the molecule that hermit crabs respond to.

And different snails - with different shells - produce different mixtures of peptides within the molecule. Hermit crabs only respond to molecules signaling the right-sized shells.

With two published papers under his belt, Rittschof was on his way. In 1980, the University of Delaware hired him to figure out what kinds of molecules tell oyster drills that living oysters are nearby. Oyster drills are predatory gastropods that drill through the shells of living oysters and eat them, costing fishers and the seafood industry millions of dollars.

His Sea Grant-funded research with the oyster drills received the prestigious Dean's Prize from the College of Marine Studies, used two million larval oyster drills and netted enough material to fill 16 research papers. Rittschof found the molecule that oyster drills respond to in the chemical "body odor" that oysters and barnacles produce. Amazingly, it is the same kind of molecule that tells hermit crabs a new shell is available.

"Evolutionarily, these are really old molecules and really old chemical-reception systems," says Rittschof. His research points to the ancient development of systems of chemical communication - perhaps so ancient that it predates the evolution of multicellular organisms. "A molecule in human blood tells all the white blood cells to creep to the site of a wound. ... The same kind of molecule tells hermit crabs that a shell is available." And it tells crabs to release their larvae, barnacle and oyster larvae to settle out of the water column, and oyster drills that they have found their lunch.

Because the molecules and the chemical communication systems that perceive them are so old, the systems are the same from animal to animal. "You can't modify the transduction system, but you can shape it to different ends," says Rittschof. Animals read different pieces of the same molecule and perform different behaviors as a result, but the medium for receiving and processing the chemical message - the hard-wired reception system - is always the same.

Rittschof's work with the chemistry of animal behavior brought him to Duke in 1982, where he was hired to develop a non-toxic anti-fouling compound based on extracts from soft corals. Existing anti-fouling paints use copper to prevent barnacle growth, but copper is a bioactive element that can be toxic in the marine environment.

Rittschof eventually received seven patents based on his anti-foulant work, but mass production of the products he developed is on hold. "Registering the compounds would take about 10 years and cost about $11 million," he explains.

So now he is once again concentrating on chemical sensory systems, isolating the bioactive enzymes in fish mucus that tell blue crab larvae and other small prey that a predator is near. With fellow researchers Richard Forward Jr. of Duke and Richard Tankersley of the Florida Institute of Technology, he also has received funds from the National Science Foundation to study how the dynamics and "smell" of estuaries influence the blue crab larvae who settle there.

In unlocking the secrets of blue crab settlement and fish "body odor," as well as developing anti-fouling paint and better fish lures, Rittschof bridges a long-standing chasm in modern science. "There are two kinds of science," he says. "Science that asks how things work, and science that applies knowledge in practical ways." Rittschof does both.

His office is a testimonial to his wide-ranging interests, and to his respect for both practical and "pure" science. On a crowded bookshelf behind his chair stands one of his patent certificates. Another shelf is dedicated to fossils he has collected, including sharks' teeth, a marlin's bill, sand dollars and a horse's molar. Chemical diagrams are scrawled on a blackboard beside his desk.

Walls and bulletin boards flutter with photographs and mementoes from students - a snapshot of "Dr. Dan" flanked by grinning coeds, a huge Chinese scroll that he insists reads "Don't worry, be happy," an inscrutable paper oval above his computer that says, simply, "Bacon." "People bring stuff in here and leave it," Rittschof says with a bemused smile. And he keeps it all: paintings and prints, an embroidered cat, an Italian "candy" made of glass.

Beyond the window lies his cherished estuary, with all its animals and their particular chemistries. Inside is the cluttered habitat Rittschof has created for himself, full of reminders of the work he loves.

"It's all about teaching and curiosity," he says.