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Examples of Evolution: Toxic River Fish
Episode 12023rd November 2021 • My AP Biology Thoughts • Hopewell Valley Student Publications Network
00:00:00 00:03:42

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My AP Biology Thoughts  

Unit 7 Natural Selection 

EPISODE TITLE: Natural Selection of the Tomcod against Pollutants

Welcome to My AP Biology Thoughts podcast, our names are Celine, Xavier, and Sofie and we are your hosts for this episode called Unit 7 Natural Selection: Examples of Evolution-Toxic River Fish. In episode 120, we will be discussing the Toxic River Fish and how it relates to the AP Biology Curriculum. 

We want to thank our sources for the information presented in this podcast episode today which include national geographic and NPR. You can find the citations and links to these sources in the show notes.

Segment 1: Overview of Toxic River Fish 

  • To begin with the overview, the species of fish we will be discussing today are the tomcod
  • This species of fish lives in the waters of New Jersey and New York, usually found in the Hudson River where pollutants and chemicals such as polychlorinated biphenyl was dumped between 1947-1976 by General Electric companies
  • Therefore they developed a gene the resulted in an immunity

Segment 2: Evidence that supports Evolution Toxic River Fish

  • We can see the evolution of Toxic River fish from the molecular Evolution that was changing in DNA sequences. 
  • When the pollutants entered the hudson river it resulted in 95% of the fish developing liver tumors.
  • The toxins from the electric company entered the nucleus of cells and For some fish it caused a distortion of DNA instructions. This would cause some to most of the fish in the river to get sick and die.
  • By chance, the Toxic River Fish had a version of that gene that tolerated the PCB and toxins
  • The toxic river fish evolved to handle dangerous chemicals that were dumped in the river and Overtime the toxic river fish that had the resistant gene did better than the fish without it
  • Technically they’re not mutants, but the chemicals did give one genetic group an advantage over the others
  • This is where survival of the fittest played a role, the fish that could resist toxins would have a higher rate of survival than those without out resistance 
  • The ability to resist the toxins caused the toxic river fish to lose some ability to cope with natural stressors like low oxygen or abnormally high temperatures but they still had advantage above other fish

Segment 3: Connection to the Curriculum

  • Biology is the study of biotic organisms, and focuses on the dynamic and behavior. Evolution is 1/12 characteristics of biology.
  • It connects to the course because it distinctly shows evolution through natural selection
  • Natural Selection: is the process to which an individual is selected to survive because of different phenotypes.
  • We can see that the toxic river fish fit to survive in the polluted ecosystems, as they adapted to the environment because of their specific phenotype. 

Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts and digital content, make sure that you visit

Joyce, C. (2011, February 17). Toxic Avengers: Pollution Drove Fish Evolution. NPR.

Minard, A. (2011, February 19). Hudson River Fish Evolve Toxic PCB Immunity. National Geographic.

Music Credits:

  • "Ice Flow" Kevin MacLeod (
  • Licensed under Creative Commons: By Attribution 4.0 License

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