In a patch of Texas where water either runs scarce or is polluted, two researchers have discovered a new fish species, the first back-boned animal identified in the state in 30 years.

The San Felipe gambusia was caught nearly seven years ago on a spring-fed tributary of the Rio Grande River bisecting a golf course. But the finding passed scientific muster just last month, when it was published in the international journal Copeia.

"It was clear that this was something different," said Robert Edwards, a biologist with the University of Texas-Pan American , who was studying the endangered Devils River minnow along the San Felipe Creek with Gary Garrett, a state biologist, when they found the new species, about the size of guppy.

"But it took awhile for us to figure out that nobody had ever seen this sucker before," he said.

Many springs in West Texas and New Mexico have their own unique gambusia, a group known as mosquito fish, because they feed on the blood-sucking insects' young. Edwards had always thought it odd that San Felipe Springs, the third largest spring in Texas, didn't have one.

But outside of the deep ocean, most fish species have already been recorded.

In Texas, the last fish species was discovered more than 30 years ago. It too was a gambusia, found in the San Marcos River in Central Texas. And with fertilizers and pesticides running into the stream from the golf course, and the creek the only source of water for the small city of Del Rio, the odds of finding something were long.

"There are not very many more fish to be found in the United States, other than the oceanic depths. Finding a new species is kind of special, regardless of where you find it," said Clark Hubbs, 82, a professor emeritus at the University of Texas at Austin who was the inspiration for the species' Latin name, Gambusia clarkhubbsi. Hubbs has studied mosquito fish since 1938, and has himself found six new species and has four others named after him.

But about four years ago, the San Felipe Country Club, which leases the nine-hole golf course from the city, started letting the land around the creek go wild out of concern for the endangered Devils River minnow. It cut down on fertilizers and pesticides, and stopped mowing up to the creek's banks.

"Even good chemicals could do harm to the fish and the game...so we left a buffer zone of no chemicals and no mowing," said Andy Dayton, 60, the former superintendent and golf pro at the club.

In 1998, a 500-year flood hit the city, scouring the creek.

It's these events, Edwards say, that could have boosted the population of the new species, making it visible. Nine other gambusia species -- which all give birth to living young, not eggs -- are known to exist in Texas, and there are 30 worldwide.

"The combination of changes helped this species," said Edwards, who has explored the creeks and rivers of West Texas looking for the Devils River minnow for more than 20 years. Since he found the first San Felipe gambusia, he's found many more.

"Now it is abundant," he said. "Before we never caught it."