Hybognathus amarus

Rio Grande Silvery Minnow

FWS Focus

Overview

Characteristics
Overview

Rio Grande silvery minnows travel in schools. The abundance of the Rio Grande silvery minnow varies from season to season and from year to year. If stream or river flows do not significantly increase during the spring, this species is less likely to spawn that year.

Scientific Name

Hybognathus amarus
Common Name
Rio Grande silvery minnow
FWS Category
Fishes
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

The maximum total length for the Rio Grande silvery minnow is about 4.6 inches. 

Characteristic category

Lifecycle

Characteristics
Reproduction

Rio Grande silvery minnow are pelagic spawners, which means they release semi-buoyant eggs that drift in the river’s current just below the surface. Reproduction normally consists of several spawning episodes over a 12-hour period by an individual, with the spawning season lasting one to two months. 

Spawning behavior includes male Rio Grande silvery minnow pursuing a single female. If a female minnow is ready to spawn, a single male will nudge her abdominal region and then wrap himself around the female. Usually, around this time, eggs and milt are released simultaneously by the female and male Rio Grande silvery minnow. 

Rio Grande silvery minnow eggs hatch within 24 to 48 hours of being fertilized, depending on water temperature. The warmer the water, the quicker the eggs develop. Water temperature also influences how quickly the Rio Grande silvery minnow go from passively drifting larvae to actively swimming larvae, which can be four to seven days after hatching. The larvae are mature and ready to spawn by the following spring.  

Lifespan

Most Rio Grande silvery minnows live only about 18 months in the wild, but some can live up to 3 years. 

Characteristic category

Behavior

Characteristics
Behavior

Rio Grande silvery minnow are considered herbivores based on its anatomy, an elongated intestinal tract. Its diet consists of algae, but may include macroinvertebrates indirectly eaten while foraging on plant material.

Characteristic category

Habitat

Characteristics
Habitat

Rio Grande silvery minnow prefer large streams with slow to moderate current flowing over silt or silt/sand substrate. Rio Grande silvery minnow typically occupy stream habitats where water depths are less than 15.75 inches and have low to moderate velocity. Such habitats include eddies formed by debris piles, pools, backwaters, embayments, shoreline, and submerged vegetation.

River or Stream

Geography

Characteristics
Range

The historic range of Rio Grande silvery minnow includes the Rio Grande and Pecos rivers in New Mexico and Texas, down to the Gulf of Mexico. The Rio Grande silvery minnow currently occupies about 7% of its historic range, and is now only found in the Rio Grande from Cochiti Dam, downstream to the in-stream flow of Elephant Butte Reservoir in New Mexico. This species is now considered extirpated from the entire Pecos River and the Rio Grande in Texas. 

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