Scientists seek to rear the yellow tang
By Jan TenBruggencate
Advertiser Science Writer
Oceanic Institute hopes to take some of the pressure off Hawai'i's reefs by learning how to reproduce prized salt-water aquarium fish in captivity, and researchers are now cheering the first big step — getting the fish to spawn.
Oceanic Institute photo
More than 200 species are collected on Hawaiian reefs and sold to the global aquarium market, including eels, crustaceans and various reef fishes. The most heavily collected is a lemon-yellow stunner called the yellow tang.
Some Hawai'i populations of yellow tang have been depleted by the global aquarium trade.
A 1998 study of Hawaiian reefs found that populations of several commonly collected species are depleted. The situation is serious enough that the Legislature has banned collecting fish for aquariums in certain areas. In addition to protecting reef ecosystems generally, such restrictions are aimed at preserving the diversity on the reefs for tourists and residents who go snorkeling.
Oceanic Institute is applying the techniques it has used to produce food fish in captivity to the tiny aquarium fish. After working with small reef fish for the past two years, the institute within the past few months has developed techniques that allow three of the most popular Hawaiian reef-caught aquarium fish — including the yellow tang — to spawn in captivity.
If researchers can overcome the next challenge — getting the larvae to grow to adults — they may be able to reduce the pressure on Hawaiian reefs to provide colorful fish for the global aquarium industry.
"The marine ornamental industry is based completely on capturing marine organisms on the reef," said Charles Laidley, a reproductive physiologist who oversaw the world's first captive spawning of the yellow tang.
Between 80,000 and 100,000 yellow tangs are shipped from Hawai'i annually. They undergo considerable stress, and most of them die before they reach the end purchaser. They can sell for up to $40 apiece when bought by someone with a home aquarium, said Tony Ostrowski, manager of Oceanic Institute's marine finfish program.
Laidley said captive-raised fish are less likely to suffer the stresses faced by wild-caught fish tossed into a captive environment, and they may be healthier, since they won't have been exposed to diseases fish can get in the wild.
The Makapu'u-based research organization's aquarium fish program has financing from the National Marine Fisheries Service and the U.S. Department of Agriculture's Center for Tropical and Subtropical Aquaculture. It has targeted the three most popular reef fish: yellow tangs and two types of pygmy angelfish, the flame angelfish and the Potter's angelfish.
Oceanic Institute photo
All three have dramatic coloration and are small, making them prizes in the aquarium trade.
Between 80,000 and 100,000 yellow tangs are shipped from Hawai'i annually for sale to aquarium collectors.
Laidley said other researchers have been able to get angelfish to spawn, but the Oceanic Institute program, using disease control, diet and careful management, has managed spawning volumes up to 10 times those previously known.
With the yellow tang, it took a year-and-a-half to get them to spawn, or produce fertilized eggs. It was something the worldwide aquarium industry has been working on without success for two decades, he said.
The eggs hatch in a day or so, and the resulting larvae feed on a yolk sac for about a week as they begin to feed.
The problem: Nobody knows what they eat. All of the tang larvae and most of the angelfish die when the yolks are used up.
"The real bottleneck is in the larval stage," Ostrowski said.
Other research efforts at the institute have found food sources for food fish like moi, mullet and milkfish, but the tiny crustaceans eaten by the larval forms of those fish are far too big for the aquarium fish.
Miniscule crustaceans called a rotifers and others called an artemia or brine shrimp are in the range of a hundredth of an inch across, and work fine as food for the big larvae.
But pygmy angelfish and yellow tang larvae need food a quarter that size. Their mouths simply aren't big enough for the larger foods.
Laidley said Oceanic Institute's team has been able to get angelfish to survive up to 18 days by providing them with a slurry of diverse wild-caught microscopic organisms. That means they're finding something to eat, but researchers still aren't sure what, or why they don't live any longer.
The ultimate food might be immature marine crustaceans called copepods, and might also need to include some algae.
"We've tested a variety of organisms. Some are the right size, but the larvae don't survive," Ostrowski said.
The aquarium fish program at the institute started in 1999. Researchers know how to reproduce in captivity only about 30 of the 800 species of wild-collected aquarium fishes. Laidley said he is sure that he and larval physiologist Robin Shields will within a year or two develop the techniques required to take yellow tangs and the pygmy angelfish through complete life cycles.
"We don't have it wired, but we know it can be done," Laidley said.
