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Study: Potential Effects of Wastewater Discharge on the Santa Anna Sucker

Date Posted: January 12, 2010

The federally threatened Santa Ana sucker currently inhabits three disjunct areas in southern California. Threats to this native fish include alterations of natural stream hydrology from dam construction and operations; loss of habitat to development; and decline in water quality.  Recently, interest in determining whether alterations in water quality may also negatively impact the breeding success of the sucker prompted a research study to determine the types and concentrations of certain chemical compounds present in waters inhabited by the fish.  The study focused on determining if Santa Ana suckers are being potentially exposed to organic wastewater compounds and endocrine disrupting compounds.

The federally threatened Santa Ana sucker. photo: Paul Barrett, USFWS

The federally threatened Santa Ana sucker. photo: Paul Barrett, USFWS

Endocrine disrupting compounds have the potential to affect growth and reproduction in both animals and people. A variety of compounds have been identified as potential endocrine disruptors, including prescription and non-prescription drugs, steroids, insect repellents, fragrances, and fire retardants.

Western mosquitofish were used for the study as a surrogate for the Santa Ana sucker because mosquitofish are abundant in the areas where suckers are found; they have strong site fidelity, meaning they spend their lives in the same area; and they are easily caught.

  The Teriary Treated Wastewater Effluent pipe draining into the Santa Ana River.  Photo: Judy Gibson/USFWS
The Teriary Treated Wastewater Effluent pipe draining into the Santa Ana River. Photo: Judy Gibson/USFWS
Contaminants experts from the U.S. Fish and Wildlife, along with scientists from the U.S. Geological Survey, and other entities, captured adult mosquitofish from five sites – immediately adjacent to a Tertiary Treated Wastewater Effluent (TTWE) pipe and the Rialto Drain; Sunnyslope Creek; and Prado Dam. A control site at Thousand Palms Oasis was used for sampling because it is closed off from any direct outflows of treated wastewater. The mosquitofish were collected from all sites during the month of June 2004 and June 2005.

In addition to collecting adult mosquitofish, two separate types of passive water sampling devices were placed at each of the study sites – a Polar Organic Chemical Integrative Sampler to capture hydrophilic compounds (pharmaceuticals, personal care products); and a Semipermeable Membrane Device used to capture bioaccumulative hydrophobic organic compounds.

Researchers wanted to determine whether compounds in the water where the Santa Ana sucker lives might have potential effects on the species’ reproduction. To assess potential reproductive effects researchers looked at sperm counts and sperm motility of male mosquitofish; compared gonopodial lengths; and counted the number of hooks and serrae present near the gonopodial tip because these are used by the males to grasp females during mating.

Researchers specifically tested for the presence of 28 different chemical and organic compounds at each of the sampling sites. Chemical analysis was conducted for various compounds and emerging contaminants, including those not regulated or monitored in discharger effluents.

The following Table shows what percentage of the different compounds were found at each site.

Sample Site

Percent of Compounds Detected



Rialto Drain


Prado Dam


Sunnyslope Creek


Thousand Palms Oasis


It was clear that the amount of compounds present in the water decreased the further away from the source point one sampled, with the control site having the far fewest detections.

Beyond this information, the next step was look at the specific attributes of the mosquitofish from each of those sample sites to determine if there were significant differences in sexual organ development.

Several secondary sex characteristics in sampled male mosquitofish showed impairment compared with the reference site. For example, the gonopodial hooks and serrae were significantly lower at all the sites along the Santa Ana River (TTWE, Rialto Dam, Prado Dam, Sunnylsope Creek); and sperm motilities, counts, and percentage of mature cells were lower at the sites along the Santa Ana River, although overall there was no demonstrable difference in viability of the sperm.

Although numerous organic wastewater and endocrine disrupting compounds were detected at all sites along the Santa Ana River, the study could not pinpoint a specific compound as being the primary cause of reproductive impairment. However, multiple lines of evidence for impaired reproductive and endocrine function in western mosquitofish due to organic wastewater and endocrine disrupting compounds found in the Santa Ana River can signal potential reproductive impairment for the Santa Ana sucker inhabiting the same and nearby sites.

To promote a healthy environment for both wildlife and people, the U.S. Fish and Wildlife Service has partnered with the American Pharmacists Association, and the Pharmaceutical Research and Manufacturers of American to launch the SMARxT Disposal campaign

The SMARxT Disposal campaign aims to educate people about ways to dispose of unwarranted medications in a safe and environmentally protective manner.


 Jane Hendron,

Carlsbad Fish and Wildlife Office

Division of Environmental Contaminants:
 - Endocrine Disruptors
 - Water Quality

Endangered Species Program

Last updated: June 12, 2015