Of all the talents needed by scientists, one of the most surprising is creativity. To solve problems and answer questions, scientists need to think in new ways. Albert Einstein once said, “I am enough the artist to draw freely upon my imagination. Imagination is more important than knowledge.” Einstein meant that to discover new things, we must use our imagination and our creativity.

In this research, you will read about a creative way to study fish. The scientist in this study used his imagination and technology to learn something new about a small minnow that lives in the Rio Grande. The Rio Grande is a river in the Southwestern United States.

The Rio Grande is a long river. The Rio Grande’s headwaters are in Colorado. The river runs through Colorado and New Mexico. The river leaves New Mexico and forms part of the United States boundary with Mexico in Texas (figure 1).

Figure 1. The Rio Grande flows from Colorado and eventually forms part of the United States boundary with Mexico.

In the past, the Rio Grande was a wide, shallow, meandering river (figure 2).

In the 1940s, people began to change the river. They created dams to control floods (figure 3). People also dug channels to divert water from the river to their agricultural fields. The Rio Grande is different today than it was before the 1940s.

Because of the changes made to the Rio Grande since the 1940s, the river now provides a lower quality habitat for some fish and other aquatic animals. Some of the fish that thrived before the 1940s are not doing as well in the changed Rio Grande. One of these fish is the Rio Grande silvery minnow (Hybognathus amarus) (figure 4).

In the past, the silvery minnow was the most abundant fish in the river. Now, the silvery minnow is listed as endangered by the U.S. Fish and Wildlife Service. When a species is listed as endangered, it means its population may disappear in all or in many of the areas where it lives.

Many changes have occurred in the Rio Grande since the 1940s. (See “Thinking About the Environment.”) These changes created a river that is deeper and faster. This different habitat has created problems for the Rio Grande silvery minnow population. So few silvery minnows now live in the Rio Grande, the fish is in danger of becoming extinct.

To rebuild the population of Rio Grande silvery minnows, biologists raise the minnows in fish hatcheries (figures 6a and 6b).

Biologists feed the minnows in the hatcheries with food that is made in factories (figure 7). This food is unlike the minnows’ natural food. When the minnows are released into the Rio Grande, 95 percent of them starve or are eaten by other animals. Some scientists believe that the minnows starve because they do not recognize their natural food sources.

The scientist in this study was interested in the natural diet of silvery minnows. Silvery minnows are mostly plant-eaters. Young silvery minnows eat algae. The type of algae they feed on is made up of diatoms.

The scientist thought that silvery minnows raised in fish hatcheries could be taught to recognize and eat natural food sources, such as diatoms. If silvery minnows could learn to recognize natural food sources while in hatcheries, fewer might die of starvation after their release into the Rio Grande. If fewer minnows die of starvation, the silvery minnow population might be saved from extinction.

The scientist wanted to answer this question: Can young silvery minnows be taught to recognize natural food sources such as diatoms?

The scientist used eight aquaria. (Aquaria is the plural form of aquarium.) Each aquarium held 37.85 liters (10 gallons) of water. Two of the aquaria were used for holding fish. Six of the aquaria were used for feeding trials. The scientist randomly selected young fish from the two aquaria. Then, the scientist placed 1 fish in each of the six aquaria until 10 fish were in each aquarium (figure 9).

The scientist grew diatom colonies in petri dishes (figures 10 and 11). In this case, a colony is like a community consisting of a large number of tiny organisms. As if using a cookie cutter, the scientist used a cylinder to remove part of the diatom colony from the petri dish. The resulting piece of the diatom colony looked like a hockey puck. The scientist, therefore, called the diatom colony pieces “pucks.”

The scientist placed 6 pucks each on 6 pieces of Plexiglass®. Each puck was the same distance apart. Each piece of Plexiglass® was placed into an aquarium holding the 10 young minnows. To observe the fish, the scientist videotaped each aquarium. The scientist could, therefore, view the video later and observe the fish (figure 12). The scientist timed the number of minutes it took young minnows to locate and sample diatoms from the pucks. This process was repeated six different times.

The scientist then waited between 5 and 17 days. During this time, he fed the young minnows regular aquarium flake food. He then repeated the process used before with the pucks. The purpose of this experiment was to determine whether young minnows that had previous experience would quickly recognize their natural food.

The scientist found that minnows not previously exposed to pucks took an average of 250 seconds to locate the pucks and sample the diatoms (figure 13). Minnows introduced previously to pucks took an average of 49 seconds to begin feeding. Some of the minnows began eating from the pucks within 4 seconds.

This study’s purpose was to discover if young silvery minnows can learn to quickly recognize and feed on natural foods. If the minnows can learn, they may have a better chance of survival after being released into the Rio Grande. Some silvery minnows learned to locate natural food after just 30 seconds. Days to weeks later, they remembered what they learned. They quickly located the natural food and began eating.

The scientist observed that once the first minnow began eating, other minnows quickly joined. Another advantage of training minnows is that a trained minnow might be a role model for other minnows. If untrained minnows see a trained minnow sampling a natural food, the untrained minnows may also try the food.

The scientist believes that silvery minnows hatched and raised in fish hatcheries can be taught to identify natural foods. This teaching may help prevent the silvery minnow population from becoming extinct.