Nevada removed invasive blue tilapia from Moapa dace habitat from 2009 to 2012; the endangered fish later returned to an 868-meter stretch where it had vanished

The return of an endangered fish to a stream where it had disappeared for years shows how controlling invasive species can help restore damaged freshwater habitats. In Nevada, conservation teams targeted non-native blue tilapia that threatened the survival of Moapa dace, a small fish found naturally only in the warm springs and streams of the Muddy River system. The effort, carried out between 2009 and 2012, formed part of a wider conservation program to protect the rare fish. Subsequent monitoring recorded Moapa dace returning to an 868-metre stretch of Big Muddy Creek, demonstrating how invasive-fish control and improved habitat connectivity can support the recovery of a threatened species.

A rare fish under pressure

According to the IUCN Red List, Moapa dace (Moapa coriacea) is a Critically Endangered fish native to the warm spring-fed streams of the Moapa Valley in Clark County, Nevada. Its restricted distribution makes it vulnerable to changes in water availability, habitat degradation and the introduction of non-native fish. One of the problems was caused by blue tilapia (Oreochromis aureus), a non-native fish that has become established in the upper Muddy River system. Exotic fish may compete with native species and prey on smaller fish, further endangering an already threatened species. The introduction of tilapia has made it difficult to keep adequate habitat for the Moapa dace.


A study published in PLOS ONE examined environmental conditions associated with Moapa dace habitat, highlighting the importance of suitable water flows and conditions in the spring system. Protecting the fish required more than simply monitoring its numbers. Conservation teams also needed to reduce the pressures caused by invasive species and ensure that suitable stretches of stream remained accessible.

Removing invasive tilapia and reopening habitat

From 2009 to 2012, Nevada wildlife management authorities conducted blue tilapia removal operations in parts of the upper Muddy River system. Rotenone, a chemical fish-killing agent, was used to remove non-native fish species from particular river reaches. The removal effort involved the Nevada Department of Wildlife, the US Fish and Wildlife Service, and the Southern Nevada Water Authority.

Removing tilapia helped reduce a major threat, but the recovery of Moapa dace also depended on whether the native fish could reach suitable habitat. Barriers intended to restrict the spread of invasive fish limited movement through parts of the stream network. Subsequent management changes allowed Moapa dace to recolonise some areas where it had previously disappeared.

The Big Muddy Creek provided another example. The IUCN case study documented one Moapa dace sighting in August 2011 and another in February 2012. No further fish were detected in the reach until February 2015. The population then appeared to recover gradually. By February 2018, monitoring recorded an average of 32 Moapa dace in the 868-metre reach.

Why the recovery remains incomplete

Reintroduction of Moapa dace into Big Muddy Creek indicated that fish control could play an important role in the recovery process, along with actions that increased access to suitable habitat. Nevertheless, the species was considered vulnerable as large parts of its historic range were left unoccupied. An IUCN case study in Global Conservation Translocation Perspectives also notes that Moapa dace had historically occupied around 38% of the stream habitat. Other methods for conservation of the species included increasing the availability of a good habitat. This included creating a new 400-metre stretch of Lower Pederson Stream with pools and flowing water designed to meet the fish's habitat needs. The fish naturally recolonised it, with about 200 to 600 Moapa dace recorded there.

Sustained recovery relies on ensuring appropriate streamflows, safeguarding the warm springs, monitoring the fish populations, and preventing the recurrence of any invasive species. This is especially critical in a desert environment, where groundwater extraction and changes in streamflow could further reduce habitat availability.