FISHING

To farm fish, first you have to catch some

 

UM scientists go fishing to catch breeding stock for their experimental mahi-mahi hatchery.

scocking@MiamiHerald.com

There’s a lot more to aquaculture than growing fish in laboratory tanks at the University of Miami’s experimental hatchery on Virginia Key.

Before researchers can raise mahi mahi (dolphin fish), for example, they’ve got to catch brood stock. And that’s how aquaculture program head Dan Benetti and four colleagues spent Tuesday: catching a dozen dolphin in a half-day outing aboard the Coconut Grove-based charterboat Miss Britt II.

“These are perfect-sized fish,” research assistant John Stieglitz said happily of the 22- to 24-inch mahis that included three junior bulls and nine junior cows. “These will spawn tonight.”

The marine lab rats were caught around a large patch of sargassum weed in about 800 feet of water off Miami Beach. They ate live pilchards cast by the scientists and crew members Ryan Preston and Ryan Peters. None went into the fish box but instead were placed in a round, 300-gallon aerated plastic tank in Miss Britt’s cockpit. The scientists pumped in pure oxygen and raw sea water to keep the fish lively for the trip back to the hatchery.

The three-year-old dolphin-raising program has a two-fold purpose: to develop a technology package for food production and, just recently, to test the effects of the 2010 Deepwater Horizon oil disaster in the Gulf on pelagic fish.

“Without the aquaculture, we wouldn’t be able to do the research on the toxicology,” Steiglitz said. “Everybody thinks aquaculture is just about food production, but it’s about allowing us to work with these challenging pelagics in captivity.”

Because research is ongoing and the Gulf oil spill is still being litigated, the scientists aren’t discussing their findings about the effects of oil on fish exposed to it. But they say they’ve come a long way in understanding the mahi and can show fish farmers how to raise this popular food and sport species with techniques that are both economically and environmentally sound.

Compared to other fish, the mahi grows very fast — from tiny larva to reproductive adult in three to four months and weighing right around a pound. Benetti says UM’s tank dwellers spawn constantly. He said their lifespan is only about four years, and they can reach weights of 100 pounds in two years. Growing too large for their tanks, they often leap out and commit suicide and must be replaced a couple times a year.

The mahi’s robust reproduction and growth, Benetti said, so far has kept wild stocks at sustainable levels despite intensive, commercial longline fisheries off Peru, Ecuador and Costa Rica.

“Thankfully, mahi are resilient,” Benetti said. “They are promiscuous, premature and precocious. But eventually you might have a threshold where the population may not be able to recover. We have the technology package when and if that time comes. We’ll be ready when they are.”

Marine aquaculture has been criticized in some quarters for depending on fish oil from menhaden and other species to nourish farm-raised fish. But Benetti and his colleagues say their methods are more efficient than those used in beef production And, they say, they’ve replaced some fish oil with plant-based protein such as soybean oil. They also raise their own plankton to feed the mahi in their larval stages. Larger fish are fed squid and sardines plus other nutritional supplements.

Dolphin aren’t the only fishy projects conducted at the UM hatchery. The scientists also have raised cobia, goggle eyes (an important bait fish species), and pompano. A blackfin tuna project is on hold, but now Benetti is seeking grant funding to raise red snapper for restocking in the Gulf.

“I’m confident we can mass-produce them for restocking,” he said. There’s high mortality. We know we’ll lose some, but we’ll keep some. It’s very challenging. Our goal will be science-based stock enhancement.”

Meanwhile, catching laboratory animals is one of the more fun parts of the aquaculture team’s job. They thoroughly enjoyed the outing on the Miss Britt.

“The way they light up,” Stieglitz said of the flashing, feeding mahis. “A special fish. Life in the fast lane.”

It was a rewarding trip for captain Sean Lue, who was running the boat for owner/captain Ray Rosher.

Lue, a veteran offshore sportfishing captain who has chased large pelagic gamefish around the world, said he has noticed a decline in dolphin fish in recent years. He was glad to guide the UM researchers.

“A change of pace for us — penning them up,” Lue said of the dolphin. “It’s pretty cool.”

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