Hooked on fish

Friday, Jan. 24, 2003 | 3:18 a.m.

WEEKEND EDITION: Jan. 25, 2003

A University of Nevada, Las Vegas graduate student is studying how well fish grow as they move to northern climes.

His work has helped bring a 155-year-old study on warm-blooded animals into question.

When Derek Houston was working on a master's degree in biology at Brigham Young University, his adviser, Mark Belk, suggested reviewing decades of studies about how animals grow.

The two researchers discovered that fish were included in a scientific theory dating from 1847 that says animals grow larger as they go north. However, the theory was based on research in which scientists measured fish in ponds and pools with changing water temperatures.

Houston and Belk decided to test the theory in the native waters of fish. And they discovered that fish didn't fit into the animal theory.

Belk and Houston's findings on fish growth were published in December's issue of the journal The American Naturalist.

Warm-blooded animals, according to the original study, grew bigger the farther they traveled north. Mammals fit the pattern, but some scientists had automatically included fish in the theory.

"Most people assumed fish were included, but it was based on laboratory observation, not the natural environment," Houston said.

First, Houston spent hours on the Internet and at the BYU library searching for any reports of body sizes of different fish populations.

"Unfortunately, we didn't get to travel all over the U.S.," he said. "Mostly we worked in the library."

Belk, a member of Brigham Young University's integrative biology department, and Houston studied fishes of the Great Basin, which includes most of Nevada, southern Idaho and the western edge of Utah.

From 18 freshwater species collected at 16 locations ranging more than 350 miles north to south, the scientists concluded that the farther north they live, the smaller fish are, usually by as much as inches.

"Basically, we found out that fish don't follow the rule for mammals," Houston said.

Bass, walleyes, chubs and suckerfish were all part of the study.

Why would a cutthroat trout from Utah be larger than ones caught in northern Wyoming's waters?

Houston and Belk suspect lower water temperatures and shorter growing seasons could account for the smaller fish at higher latitudes, Houston said.

Since fish are cold-blooded, they take on the temperature of the surrounding environment.

If rivers, lakes and streams become too cold, fish metabolism slows down, a possible way to explain why they grow slower in colder climates.

Warm-blooded mammals, after all, have fur or feathers to keep them warm, allowing their growth to continue and even accelerate slightly in cold weather.

However, there is no final answer as to why animals grow larger in northern locations.

That is one reason Houston plans to continue his studies at UNLV.

Houston has graduated from BYU with his master's degree in biology. He said he is starting his coursework for a doctorate and expects the degree, which he plans to get at UNLV, to take him up to four years.

For his doctorate, Houston plans to look at a species of minnow that roams from the Great Basin to the Rocky Mountains as far away as British Columbia to try and answer some questions that were spawned during his master's degree work.

The red side shiner minnow is a smaller-bodied fish that changed its maximum growth. There are gaps in the knowledge to follow, Houston said.

"You always have too many questions you'd like to answer," Houston said, "and the minnow is kind of a pretty fish, too."

As he pursues his Ph.D., Houston said he is looking at the range of the minnow and its physical changes, an emerging field known as biogeography.