But the 4-month-old tropical queen triggerfish, which can grow to a foot and a half long with iridescent yellows and blues, are the first triggerfish to be raised in captivity. And if researchers perfect their technique, other marine aquarium fish - including threatened ones like the queen trigger - could be raised in hatcheries instead of taken out of the wild.

“We grew them on the first real try,’’ Andy Rhyne, assistant professor of biology at Roger Williams and a research scientist at New England Aquarium, said as he gazed at the three wriggling fish with a smile. “It’s a springboard.’’

Roger Williams and aquarium researchers teamed up to overcome a decades-old obstacle to growing many kinds of marine fish: feeding them when they are young.

Today, the vast majority of freshwater fish in home aquariums are produced by aquaculture. Freshwater fish tend to be relatively easy to grow because their larvae are large, some can be fed dry food, or scientists have been working on them so long that they know how best to make them grow.

But most marine fish larvae are smaller and require a live meal. Researchers have met with limited success feeding larvae tiny aquatic animals called rotifers. Those organisms can grow fast and at great densities, but are often too big to be fed to marine fish or do not have the nutritional punch they need.

As a result, only a tiny percentage of marine aquarium fish are grown by aquaculture. Most are caught in the wild. But there are problems: Some species are overfished, while others are caught in damaging and often deadly ways, such as by squirting cyanide into reefs to anesthetize the fish so collectors can gather them.

In the ocean, marine fish larvae eat copepods - tiny crustaceans found virtually everywhere. But raising copepods in the lab is extraordinarily difficult. The tiny animals have complicated temperature, salinity, and food requirements.

“People have cultivated copepods over the years in moderate quantities, but no one has been able to do it in bulk,’’ said Nancy Marcus, a copepod specialist and dean of the graduate school at Florida State University.

Rhyne, along with colleague Erik Stenn, who has an algae biotech company, were having some success with copepods in Florida. Rhyne was hired in August in a novel arrangement between the aquarium and Roger Williams to study larval fish production at the aquarium and start a program in aquarium science and aquaculture at the university.

Triggerfish seemed a natural species to attempt to grow - and one that New England Aquarium scientists had tried for years to rear. Queen triggers grow too large to be a popular home aquarium fish, but their size and coloration have made them popular in public aquariums. Since they are threatened, Rhyne and Michael Tlusty, the aquarium’s director of research, figured if they could grow a queen trigger, aquariums would not have to take them from the wild.

This summer, researchers collected tens of thousands of queen triggerfish eggs from one nest in the aquarium’s giant ocean tank and brought them to the marine lab at Roger Williams, overlooking Narragansett Bay. Thousands hatched, but the team focused on a relatively small number to feed with a local species of copepod they were growing. Most died, but today four remain alive - three at Roger Williams and one at the aquarium - and all have grown large enough to be fed dry food.

There is a long way to go, Rhyne said: Copepods are still incredibly fussy to raise. But he said he is getting closer to figuring out how to raise large quantities of them. And the fact they grew a triggerfish with the copepods gives the scientists hope that other species could be grown in the same way for public aquariums.

Their work may also one day affect the estimated $250 million trade in ornamental marine fish - some species of triggerfish are worth $500 each. Even if businesses raise only small amounts of copepods, it could be profitable because the fish are so expensive.

“There is a lot of economic pressure to [raise] marine fish,’’ said David Lass of Nahant, an aquarium fish specialist.

But the ability to raise marine hobby fish comes with great responsibility, Tlusty said. Many are caught in an environmentally responsible way and serve as a key economic engine to impoverished areas of the world. In some cases, the fish collecting provides revenue - and incentives - to keep swaths of reefs conserved.

“It really needs to be put in a global perspective,’’ Tlusty said. “You can’t start producing every marine species in captivity.’’

Still, he said, raising the marine fish is exciting.

“When I came here 10 years ago, there was a proposal floating around to raise triggerfish. It’s exciting [we did it] but it points out the enormous amount of work that still needs to be done.’’

Beth Daley can be reached at bdaley@globe.com.