Foods of Age-0 Rio Grande Silvery Minnows (Hybognathus Amarus) Reared in Hatchery Ponds (Report‪)‬

The Rio Grande silvery minnow Hybognathus amarus historically occurred in the Rio Grande from Espanola, New Mexico, to the Gulf of Mexico, and in the Pecos River from Santa Rosa, New Mexico, to the Rio Grande (Bestgen and Platania, 1991). Local and widespread fragmentation of rivers by diversions of water and reservoirs, dewatering of mainstem reaches, introductions of congener plains minnow H. placitus, and nutrient enrichment are likely causes of range-wide reductions in occurrence and abundance (Bestgen and Propst, 1996). Consequently, this once widespread and abundant fish was extirpated from the Pecos River and the Rio Grande in Texas by the 1960s (Bestgen and Platania, 1991; Hubbs et al., 1991), prompting listing of the fish as an endangered species (United States Department of the Interior, 1994). Currently, the Rio Grande silvery minnow occurs only in a 280-km section of the Rio Grande between Cochiti Reservoir and Elephant Butte Reservoir in New Mexico (United States Fish and Wildlife Service, 1999, 2007). However, persistence of Rio Grande silvery minnows in this section of the Rio Grande is tenuous because of introductions of exotic fish and continued degradation of water quantity and quality (Bestgen and Propst, 1996). As such, wild stocks are supplemented by hatchery-reared fish. The primary goal of the Rio Grande silvery minnow recovery plan (United States Fish and Wildlife Service, 1999, 2007) is to prevent extinction of the Rio Grande silvery minnow in the middle Rio Grande; captive propagation is the main tool for achieving this goal. Dexter National Fish Hatchery and Technology Center (Dexter, Chaves County, New Mexico) is a 267-ha facility with specific responsibilities for the propagation, culture, and research of threatened and endangered aquatic species. Propagation of the Rio Grande silvery minnow began at Dexter National Fish Hatchery and Technology Center in 2001 with an emphasis placed on development and refinement of captive-propagation and rearing techniques. As of 2008, Dexter National Fish Hatchery and Technology Center produced ca. 300,000 Rio Grande silvery minnows/year and, along with other facilities, has released 1,000,000 hatchery-reared fish into a 280-km section of the Rio Grande. In December 2008, Rio Grande silvery minnows from Dexter National Fish Hatchery and Technology Center (250,000 age 0 and 150,000 age 1) were used for a historic reintroduction into the Big Bend reach of the Rio Grande in Texas and Mexico, with plans to stock an additional 100,000 fish/year through 2012.