ominique Didier Dagit has her arms full with a ratfish residing in a tank in the Academy of Natural Sciences. (Akira Suwa / Inquirer Staff Photographer)

Where do they lay eggs?

Why do ratfish embryos wiggle their tails in their egg cases?

How did they remain so primitive and not evolve like their cousin, the shark?

And what, exactly, are they doing down there in the deep, deep ocean?

Dagit has a boat-load of questions. Questions that nobody else is likely to have the answers to since she is the world's leading expert on the ratfish.

In fact, she is the only expert on ratfish.

"I guess nobody else found them interesting," said the 34-year-old Dagit. "Some people think they're ugly. But I think they are very cool."

The ratfish has been a passion since her days as an undergraduate at Illinois Wesleyan University. Casting around for a senior biology project, Dagit's advisor suggested the ratfish. It was love at first sight.

Today, as the Academy of Natural Science's associate curator for ichthyology, Dagit - a resident of Conshohocken and passionate rollerblader - continues to labor in one obscure corner of marine biology. But she is certainly mistress of that domain.

There are 42 known species of ratfish - most in the family Chimaeridae. They evolved 300 million years ago in the oceans of the Carboniferous Period.

Deepwater denizens, the fish are usually found between 1,500 and 9,000 feet below the surface and range in length from a few inches to about four feet.

A few species are caught commercially, but not much else is known about them.

What little is comes from a string of Dagit research papers with titles such as "Embryonic Staging and External Features of Development of the Chimaeroid Fish."

But really, does it matter? Does anyone need to know the mating habits of an obscure, slimy, shiny-green-eyed fish?

"The ocean is really the last great unknown on the planet," Dagit said. "We increasingly depend upon it for food, but we don't really know what's in it or how it works."

The only way to answer those questions, Dagit believes, is sea by sea, fish by fish.

It is also a grand adventure. "We know that there is new stuff in the ocean waiting to be discovered," she said. "It is like knowing that there is a monster just lurking in your closet."

Sometimes, Dagit spends a day working on fishing boats for free - under the agreement that she gets her dinner and can keep anything interesting that gets tangled in the nets.

Her latest project is to go scuba diving in the lagoons of the Aldabra Islands - several hundred miles southwest of the Indian Ocean's Seychelle Islands - to find shark spawning grounds.

Dagit's search is not without a sense of urgency. As traditional fisheries - cod and flounder - become more limited and costly, fishermen have cast their nets more widely and hauled in a broader variety of fish for the market and dinner table. Many of these species - spiny dogfish, skates, orange roughy and ratfish - used to be considered "junk" fish.

"They are pulling up 30,000 tons of ratfish a year in New Zealand," Dagit said. "Is that sustainable? What will it do to the ecosystem? The answer is we don't know."

The questions Dagit asks are big, but the answers tend to come in bits. For example, she spent most of this summer neither scuba diving nor riding fishing boats, but sitting at a lab table in a windowless room.

The problem before her was a tiny one: What does the tail of a ratfish embryo look like and how does it form?

John Long, a biologist at Vassar College, is studying the development of the skate and asked Dagit to compare the tails of skate and ratfish embryos for him.

The tail is important in both animals because the embryo swims around its egg case, creating a flow of water through the case.

Long was hoping that Dagit might be able to shed some light on the process by comparing the nerve and muscle development of the two related fish.

A small question, but a complicated one.

Dagit just happened to have some ratfish embryos, from Callorhinchus milii, that she had collected in New Zealand. Using a scalpel, she cut off the tails and used ethanol to remove all the water from the tissues.

Then the embryo tails were placed in hot paraffin and allowed to cool into wax blocks.

Each block was placed on the microtome - the scientific equivalent of the deli meat slicer - and shaved into 10-micron slices, thinner than a human hair.

Each slice was then placed on a slide and dipped into a succession of stain baths. Cartilage turned bright blue. Nerves light blue. Skin orange. Muscle deep red. Blood pale, orangey red.

Finally, it was back to the microscope. Dagit worked slide by slide examining the tail sections, recreating the image in her mind and sketching into a hard-cover composition notebook, like the ones used by school children.

"Look at all the neuromasts," Dagit said as she peered into the microscope. "They're all over the place."

Why, she wondered, did these specialized sensory cells, which detect motion, appear all over the embryo's tail but in only a few places in the adult? "One more question that needs to be answered."

As she moved the slide around the microscope stage, Dagit sketched. "Ah, here's the circular muscle, it doesn't go all the way to the tail. Now that's interesting."

It had taken nearly four days of preparation to get the slides ready for the microscope and several more hours to analyze the sections and write a description for the biologist at Vassar.

"All this work will probably end up as one paragraph in a paper that nobody reads," Dagit said, "but, you know, that's science."

© 1998 Philadelphia Newspapers Inc.