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Hero of Aquatic Toxicology: The Fathead Minnow

What is aquatic toxicology testing?

Aquatic toxicology testing evaluates the direct impact a substance has on living organisms in aquatic environments. This field of study includes freshwater, marine water, and sediment environments. Chronic or acute toxicity can be measured in algae, crustaceans, fish, oligochaete, daphnia and other small invertebrate aquatic organisms. These tests measure endpoints such as survival, growth, or reproduction at different concentrations of the sample material. Chronic analysis typically consists of exposing organisms to a level of the material and then measuring the effects of that material in the organisms over a specified exposure time. Acute analysis typically is done by establishing the LC-50 (the lethal concentration required to kill 50% of the population) of the test compound in organisms. Products that commonly undergo toxicology testing include lubricants, oils, fuels, detergents, pet care products, cleaning materials, and other product types that may come into contact with the environment.

Toxicology testing is often a required testing component for product registration, regulatory purposes, and third party labeling for product marketing.  Many agencies like the Environmental Protection Agency (EPA), the European Union (EU), and Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulate products in the market and require test data on their ecotoxicological effects. For the Clean Water Act under the United States Environmental Protection Agency there are water quality criteria and water quality standards derived from aquatic toxicity tests.

How do Fathead Minnows come into play?

Image from gallery.nanfa.org.

 Minnows and other small fish were first used in toxicology tests on dye-works chemicals in 1863. It wasn’t until the 1950s, however, that aquatic toxicology became widely-studied, due to the growth of the pesticide industry.  Increasing interest in the environmental effects of industrial pesticides led to many aquatic toxicology studies and subsequent government regulations. The continuous development and adaptation of test methods to meet the constantly changing research and regulatory needs called for a test organism that was adaptable and a suitable general model for vertebrates. Fathead minnows (Pimephales promelas) quickly became one of the dominant models in aquatic ecotoxicology.  Independent researchers and regulatory agencies alike began to use the fathead minnow in their guidelines for the evaluation of acute and chronic toxicity of chemical products in vertebrate animals.

 What makes Fathead Minnows an ideal test organism?

 Some facts about the Fathead Minnow:

  • Appearance: 5-8cm length, clear fins, dark-olive colored bodies with dorsal and lateral stripe, yellow-white underbelly
  • Lifespan: 2-3 years in the wild, 3-4 years in captivity
  • Breeding: 16 to 26 spawnings from May to September in waters ranging from 16°C to 30°C.
  • Number of Offspring: 1000 to 100000
  • Diet: Non-insect arthropods, insects, aquatic crustaceans, zooplankton, algae phytoplankton
  • Behavior: Live in schools of familiar individuals, filter-feeders
  • Communication: Use chemical cues to differentiate between familiar and unfamiliar individuals

The Fathead Minnow possesses many qualities that make it an ideal test organism for toxicology studies- relative hardiness, large number of offspring produced, tolerance of variable temperature, pH, salinity, and turbid low-oxygen water, fair tolerance of harsh conditions, and general adaptability to controlled experimentation. Fathead minnows also have a well-defined reproductive and developmental cycle, making them easy to culture in a laboratory environment. In nature, fathead minnows can be found in a large variety of freshwater ecosystems including lakes, ponds, streams, and wetlands. It can also be found in waters that are uninhabitable by other fish, like waste drainage sites, making it a valuable test organism for studies on these waste materials’ effects on aquatic life. For these reasons the fathead minnow is an ideal test organism for studies of aquatic toxicology.

 How have Fathead Minnows impacted the industry?

A substantial amount of research has already been done using the Fathead Minnow. The widespread use of fathead minnows in the aquatic toxicology industry has resulted in a large database of information on the species. Given this large database, many official aquatic toxicology and bioaccumulation methods use fathead minnows as their standard test organism.

The outlook for the continued use of fathead minnows in aquatic toxicology is promising. The Fathead Minnow is the most viable freshwater small fish model for field monitoring and in situ toxicology testing, making it a useful model for linking field work and laboratory studies. This species also has a great potential for linking molecular diagnostics to ecological outcomes for predictive toxicology approaches in chemical testing, due to the large quantity of existing information available on it.  From the origins of aquatic toxicology testing in the 1800s to future developments, the Fathead Minnow is a true hero of toxicology.

Aquatic Toxicology at Situ Biosciences

Toxicology testing on vertebrates and invertebrates can include early life stage, juvenile, or life cycle testing:

OECD 202: Daphnia sp; Acute Immobilization

OECD 203: Fish; Acute Toxicity

OECD 210: Early Life Toxicity Test

OECD 211: Daphnia magna Reproduction Test

OECD 212:  Short Term Toxicity Test

OECD 215: Fish; Juvenile Growth Test

OECD 218/219: Sediment-Water Toxicity Test

OECD 225: Lumbriculus Toxicity Test

OPPTS 850.1035 Mysidopsis bahia; acute toxicity test

OPPTS 850.1500: Fish Life Cycle Toxicity

Aquatic plants

OECD 201: Algae Growth Inhibition Test

OECD 221: Lemna species; Growth Inhibition

OECD 238: Myriophyllum spicatum toxicity test

 

References

 

Saari, T., D. Villeneuve, G. Ankley, F. Burns, A. Cogburn, S. Deschamps, R. Jackson, R. Hoke, AND A. Schroeder. Bringing the fathead minnow into the genomic era. Midwest SETAC, Madison, WI, March 14 – 16, 2016. https://cfpub.epa.gov/si/si_public_record_report.cfm?direntryid=311435&keyword=ecosystems&subject=ecosystems%20research&showcriteria=2&fed_org_id=111&datebeginpublishedpresented=01/14/2012&dateendpublishedpresented=01/14/2017&sortby=pubdateyear

The fathead minnow in aquatic toxicology: past, present and future. Ankley GT, Villeneuve DL.  University of Nebraska – Lincoln DigitalCommons @ University of Nebraska – Lincoln. U.S. Environmental Protection Agency Papers, United States Environmental Protection Agency.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1093&context=usepapapers

Ashley Sommer. Pimephales promelas Black-head minnow. http://animaldiversity.org/accounts/Pimephales_promelas/#economic_importance_positive

Hunn, J.B., 1989. History of acute toxicity tests with fish, 1863–1987. In: Invest. Fish Control 98, US Fish and Wildlife Service, LaCrosse, WI, USA. https://pubs.usgs.gov/ifc/098/report.pdf