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April 17, 2006

TPWD Releases First Flounder Fingerlings

ROCKPORT, Texas — When two years of careful work went down the drain April 4, Texas Parks and Wildlife Department coastal fisheries workers quietly cheered.

The drain was connected to a hose, and the hose led to Little Bay, a shallow estuary in the Rockport city limits. Through that hose, nearly 1,500 fingerling flounder swam to freedom.

“This is the first time we’ve gotten to this point,” said Robert Vega, Ph.D., TPWD’s enhancement director.

Southern flounder, and many other species of flatfish around the world, have proven difficult to spawn and raise in captivity.

Building on successes in Japan, North Carolina and elsewhere, G. Joan Holt, Ph.D., a University of Texas aquaculture researcher, and the TPWD hatchery team at the CCA/CPL Marine Development Center in Corpus Christi were able to successfully induce wild-caught flounder to spawn and then to raise the larvae through their metamorphosis into flatfish and to fingerlings as much as six inches long.

Fisheries biologists said 1,500 fish — the majority of which will not survive to maturity — is a drop in the bay’s vast bucket, and is not the kind of large-scale enhancement effort that is likely to make any difference that anglers can see. Instead, they said, it was important to demonstrate that it could be done at all.

“We’re very excited about the progress we’ve been able to achieve working in collaboration with Dr. Holt,” said Vega. “I think that within a few years, if our coastal managers decide we need to develop a large-scale flounder program, we should be able to achieve that objective.”

“It was a really neat trial run with not very many animals,” said Holt, who is widely acknowledged as a leading expert on aquaculture. “Next year we have a lot of plans about how we’re going to work on it.”

Holt said that scientists are continuing to learn about how to handle flounder.

Aquaculturists can induce many fish to begin spawning by manipulating environmental factors such as water temperature and the duration of “daylight” the fish are exposed to. Some species, such as red drum, respond readily to well-understood environmental cues and can be made to spawn almost on command.

Flounder, though, are a little tougher. For instance, after inducing the big females to begin spawning in December, Holt and her researchers “turned-off” the fish — stopped the spawning process — since the Port Aransas laboratory would be emptied of staff over the holidays. Problem was, they couldn’t turn them back on when they got back.

“I think we’re continuing to learn a lot about how to spawn them. We’re continuing to do the temperature tolerances so we can figure out when to put them into the ponds,” said Holt. “We’re also looking at pigmentation problems. Everyone who works with flounder around the world has problems with pigmentation.”

Flounder typically exhibit a light-colored “bottom,” or right side, and a darker top, or left, side, which more closely matches the sandy or muddy bay bottoms they prefer. In some hatchery fish — including fingerlings released this month — the dark pigmentation on top is not complete.

Holt said that there is some concern that fish that exhibit light coloration on the “wrong” side are more vulnerable to predators. Elsewhere, where flounder also are an important commercial species, unusually pigmented individuals could be perceived as less palatable by consumers.

Holt said she and TPWD hatchery staff hoped to address pigmentation problems by varying the diet of the larval fish.

Many anglers have expressed concern about the state of flounder stocks in Texas — the species is fished commercially and recreationally here — but Mark Fisher, Ph.D., TPWD coastal fisheries science director, said flounder are doing better, especially since the late 1990s.

According to Fisher, shrimp bycatch — the inadvertent capture and killing of juvenile flounder — has the biggest impact on the fish’s success in Texas waters.

“Shrimping effort is declining, and we are seeing the flounder respond,” Fisher said. “We’re seeing an increase in the adults as well as an increase in the size of the age zero and age one fish.”

Fisher said the relative abundance of adult flounder in the state hit rock bottom in 1995, several years after the peak of shrimping activity here. Since then, by buying-back shrimping licenses and limiting new entries into the fishery, TPWD has helped reduce shrimping pressure on the coast. That, in turn said Fisher, has benefit flounder.

According to TPWD Coastal Fisheries Director Larry McKinney, Ph.D., flounder stocks in Texas waters appear to be on the rebound and that is good news coastal anglers and seafood lovers alike.

“It has taken the combined effects of regulation and license buyback to get us to this point in recovering flounder stocks,” said McKinney, “but that is not good enough, and we are looking at a range of strategies, including hatcheries, to move us further and faster to where we do want to be.”

AR 2006-04-17


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