Fish – not what leaps to mind when you think of the native wildlife of the Southwest. But the Rio Grande historically has been home to dozens of fish species – including some not found in any other river system.

The Rio Grande silvery minnow was once the most abundant fish species in the river. But by the 1960s, it had vanished from Texas.

Now, wildlife specialists are working to reintroduce this endemic, native creature.

The Rio Grande silvery minnow once flourished in the river, from the southern Rockies to the Gulf of Mexico. Three to 5 inches long, it was at the base of the food chain.

But flows in the Rio Grande have declined in the last century, as water demands from ag...