The son of an Edgartown commercial fisherman is this year's winner of the 21st annual Kids' Derby, held Saturday at the Oak Bluffs Steamship Authority Wharf. Adam Castro, 6 years old, caught a 19-inch fluke; his father is Scott Castro.

More than 250 youngsters from around the Island participated in the morning of fishing and prizes. Most of the top winners of this year's contest caught fluke - large, doormat-sized fluke.

The contest began at 6 a.m., and within a short time after sunrise, there was a long line of fishermen trying to get their fish measured. The most common fish caught at the wharf was scup, ranging from a few inches to as much as a foot in length.

Ed Jerome, president of the Martha's Vineyard Striped Bass and Bluefish Derby, said he couldn't remember a more productive day of fishing for scup. Catching scup is a tradition among the Island's youngest fishermen, yet not too many years ago the fish was scarce, and few participants in the kids' derby saw the fish.

Years ago, most Island youngsters got started catching easy wharf fish like cunners, scup and sea robins before moving on to the more esteemed bluefish and striped bass.

These days, however, "There is nothing like catching scup in the morning," said Chris Scott, a volunteer at the event. Mr. Scott, a member of the derby committee, was among the dozen or so volunteers had made the contest happen.

"If you want to catch a scup you have to think like a scup," he said, eliciting a chuckle from his colleagues.

Andrew Williamson caught the largest scup, measuring 12.25 inches. His fish earned him the year's scup title as well as a plaque. Janet Messineo of Vineyard Haven, who runs a taxidermy business, donated the plaque for the winner.

It didn't take much to catch any kind of fish, just a piece of squid on a hook. A small weight brought the hook down to the bottom, and fishermen jigged their hooks up and down to entice fish. Schools of small bait swam in and out of the spiles beneath the wharf. Anyone with keen vision could tell that there were plenty of fish participating in the contest.

Mr. Jerome and contest chairman Cooper A. Gilkes 3rd conferred to decide how many years they've been running the Saturday morning contest for youngsters. Mr. Jerome said the derby began in 1982.

The running of the kids' derby is similar to the Martha's Vineyard Rod & Gun Club's annual spring trout tournament. Fish are recorded based on length, not weight. Each fish is placed on a slippery yard stick and the length is noted.

Melvin and Betsy Hauck of Edgartown have been volunteers for many years. The two spent much of the morning lining up squirming fish for measurement. Their daughter, Morgan Hauck, 21, helped.

"We collect T-shirts, that's why we do it," said Mr. Hauck. Betsy and Morgan smiled - they obviously woke up at 5 o'clock in the morning for a more significant reason than a T-shirt.

Not far out in the water sat Ed Lepore of Vineyard Haven, who had volunteered to operate the safety boat. While no youngster has ever fallen from the wharf, Mr. Lepore was available just in case.

"This weather couldn't have been better," said Mr. Jerome. "Over the years we've had rain, we've had fog, we've had our share of bad weather. This is great."

There was one elementary school science teacher present that morning. David Faber pointed to a young girl walking away with a tiny puffer fish. Caitlyn Colley, nine, of Oak Bluffs, held the fish in the palm of her hand.

Puffer fish start out little, until they are pulled out of the water. Then they inflate their stomach with air, tripling their size.

Harrison Span, 7, of Oak Bluffs, walked up to Mrs. Hauck carrying a spider crab.

Kenya Peters-Vega, a six-year-old from Oak Bluffs, held the history of her family in her small hands. She was fishing with a conventional rod and reel belonging to her grandfather, Earl Peters. Mr. Peters estimated that the rod and reel was at least 40 years old and had been used by three generations of family members.

Participants in the contest weren't all dressed for fishing. Four-year-old Chase Silvia of Tisbury came dressed as Spider-Man. Mr. Silvia received a special award for coming in costume.

Simone Geary, four and a half, was dressed as a ballerina. She even wore a delicate plastic tiara. Her mother explained that this was her daughter's first time fishing and she just wanted to dress up.

"I am so glad we got up this early," said Melanie Bilodeau of Oak Bluffs. She stood nearby while her husband Ray coached their four-year-old son, Adam. "We set the alarm for 5:30 a.m.," Mrs. Bilodeau said. "But we talked about getting up for a half-hour before we got up.

"It's great seeing the expression on the kids's eyes when they catch a fish," she said.

Their nine-year-old son, Cole, caught an 18-inch fluke later in the morning. The big fish earned him a second place in his age group of nine to 11.

By 8:30 a.m., the fish beneath the wharf had grown shy. The turbulent waters that had moved quickly earlier in the morning were now slack.

An awards ceremony followed. Mr. Jerome reported to the crowd of over 300 youngsters and parents that the wonderful contest could not be as successful without the help of the Steamship Authority.

Contest winners are as follows: Grand overall winner: Adam Castro, 6, for a 19-inch fluke.

All the winners are for fluke, except where noted:

Youngsters eight years and younger are as follows: 1, Asa Bernard, 7, 18-inch; 2, Bryan Frasier, 6, 17 1/2-inch; 3, Joey Uva, 7, 17-inch. Nine through eleven years old: 1, Teddy Kram, 9, 19-inch; 2, Cole Bilodeau, 9, 18-inch; 3, Willoughby Smith, 11, 18-inch

Twelve through fourteen years of age: 1, Joe Young, 13, 18-inch; 2, DJ Pothier, 13, 14-inch rock bass; 3, Zack Waller, 12, 13 1/2-inch rock bass.

For their trouble, the fishermen won hats, fishing rod and tackle. All the anglers walked away from the dock and got a free T-shirt.