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Fish as environmentally relevant scientific models

Four species of fish we use at Duke University to study environmental toxicology
by

Mariah Arnold

on 19 June 2014

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Transcript of Fish as environmentally relevant scientific models

Mountaintop mining
Fathead minnows can be useful for research on the environmental impacts of mountaintop removal coal mining because the are similar to wild stream minnows.
Fathead minnow
Pimephales promelas
Males have tubercules (little horns) used to guard their nests and aerate the eggs!
Fatheads are great!
Oh la la!
Hydrocarbon hijinks
Polycylic aromatic hydrocarbons (PAHs) are toxic chemicals found in oil and soot. We use the mummichog to help model heart defects and swimming performance of fish exposed early in development.
Mummichog
Fundulus heteroclitus
Why the mummichog?
Mummichog biology
Nano-sized
Zebrafish are great models to study the toxicity of nanoparticles! For example, we study how titanium dioxide nanoparticles interact with sunlight and chemicals in the water to cause toxic effects in fish embryos.
Zebrafish
Danio rerio
The facts:
Nanoparticles are particles smaller than 100 nanometers. For comparison, a human hair can be 100,000 nanometers thick!

Visit our laboratory's website below for more information on our research and nanoparticles!

https://sites.nicholas.duke.edu/ecotoxicologylab/research/toxicology-of-nanoparticles/
Zebrafish genetics
Swim baby, swim!
Selenium in the water
Medaka are great for studying the transfer of selenium, a contaminant released by mountaintop mining, from mother fish to baby.
Medaka
The facts:
The medaka embryo
Medaka in space!
Male fathead minnows dance for females to get their attention!
After females lay their eggs, they are fertilized by the male. It takes about 4-5 days for the eggs to hatch!
Dads do the work! Males rub the eggs with their head spikes (tuburcles) to clean the eggs. They also ferociously defend the eggs from predators.
A single female zebrafish can produce over a hundred eggs, which are fertilized by the male after they are laid!
Zebrafish eggs take approximately 3-4 days to hatch and they rely on their yolk sac as food for four days after hatching
Oryzia latipes
In the laboratory, we typically spawn (breed) the medaka in the morning. Each female can produce 30-50 eggs every day!
Medaka are euryhaline, meaning they can tolerate both fresh and salt water!
Medaka were the first vertebrate in space. They traveled along with astronauts in 1994 and successfully hatched heathy babies!
The Facts
:
Fairly tolerant to a variety of water conditions
Produce a lot of eggs that develop quickly
Sexually dimorphic, meaning you can tell the boys from the girls
The genome is not sequenced, but scientists are currently working to develop a variety of molecular tools
Mummichogs can live in both fresh AND saltwater!
It takes approximately 15 days for an embryo to hatch!
Mummichogs prefer to lay their eggs on the line between water and air, meaning their eggs are extremely tough. They can even go almost completely dry for days without dying!
Dominant males develop a fat pad on their heads, leading to their name "fathead"
Rosy red fathead minnows are popular aquarium fish
Mountaintop removal coal mining: the tops of mountains are blasted off using dynamite to access the coal. The leftover rock (overburden) is placed in nearby valleys, forming a "valley fill". Valley fills bury streams and leach contaminants into the environment.
The Hobet 21 mine in southwest West Virginia is one of the largest surface mines in the United States
Selenium, a naturally occurring element, can be very toxic to fish. Selenium is released into the water during mountaintop removal coal mining. We use a laboratory fish (fathead minnows) to model selenium exposure that occurs in the wild. Trout embryos exposed to high concentrations of selenium have strange deformities, as shown by the picture on the right.
Fathead minnows prefer to lay their sticky eggs underneath a hard surface
A female fathead minnow
Mummichog eggs are really tough. They can even survive being on dry land for days!
Go to http://www.sanger.ac.uk/resources/zebrafish/genomeproject.html for more info!
Scientists can use genetic tools in the zebrafish to model biological processesd responses to disease or exposure to toxins.
The zebrafish reference genome (its entire genetic code) was annoted and published in the scientific journal
Nature
in 2013 by Dr. Kerstin Howe and colleagues.
Kerstin Howe et al. The Zebrafish Reference Genome Sequence and its Relationship to the Human Genome. Nature 496, 498–503; doi: 10.1038/nature12111
These are examples of genome analyzers used to sequence the zebrafish genome!
Why do we use fish in the laboratory?
Fish can produce a LOT of eggs! Sometimes one female can produce hundreds of eggs in one day.
These pictures represent a normal mummichog embryo (left) and an abnormal embryo (right) after PAH exposure. The heart is outlined in orange. As you can see, the PAH-exposed embryo has a "stringy" heart!
Eyes
Heart
Yolk
A newly hatched zebrafish
We can even microinject things into the mummichog egg in our experiments! The embryos develop just fine.
A tiny needle
The dividing mummichog cells
5 day old medaka embryo
Eyes
Heart
Oil droplet
Yolk
Chorion
(egg shell)
Egg fibers
Medaka eggs hatch in 7-9 days
A medaka embryo exposed to selenium. Notice the bleeding in the tail, the abnormally small size, small eyes, and lack of blood pigment.
Zebrafish originally come from the Himalayas, and can be found in places like India and Pakistan
The zebrafish aquatic habitat
The mummichog culture system
Mummichog breeding box
Medaka in a recirculating tank
Mummichog like to hide so we give them PVC tubes so they feel safe!
Male mummichogs have beautiful, bright spots to lure females into mating!
The medaka colony
Study done by J.R. Simplot Company
Fish are fun to care for and enjoyable to keep in the laboratory!
Fish are important parts of an aquatic or marine ecosystem, meaning we have to understand how they respond to environmental pollutants.
Conclusions
Visit https://sites.nicholas.duke.edu/ecotoxicologylab/ for more information on our laboratory!
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Zebrafish breeding tank
Medaka eggs have fibers that look like tiny hair that help the eggs stick together
In the laboratory, we feed our medaka brine shrimp and powdered food
Wild fathead minnows are found in watersheds throughout the East coast of the U.S.
Laboratory fish typically live 3-4 years
Dominant males develop large fat pads on their heads and black/silver stripes
The average length is approximately 2 inches, although males are usually larger than females
Transgenic strains (zebrafish with extra genes added in by scientists) have been created to study human disease
Zebrafish eggs are transparent, meaning they are great models for studying development because we can watch them grow!
Zebrafish have blue stripes and males have a yellow belly
Fish are fun to care for and enjoyable to keep in the laboratory!
Fish are important parts of an aquatic or marine ecosystem, meaning we have to understand how they respond to environmental pollutants.
You can watch fish develop...in the egg!
Compared to mice and rats, fish are easy to maintain, but we always make sure their water quality is top notch!
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