As a high school student, one of the ways I earned money was by raising freshwater tropical fishes for the home aquarium market. My basement was filled with all manner of watertight vessels, from large conventional aquariums to empty 50-gallon tanks and old bathtubs. Live-bearing fishes, like guppies, were both pretty and easy to raise; egg-layers took more time and effort.
One cooperative and prolific egg-layer I raised was the zebrafish (Danio rerio). This one- to two-inch critter is a relative of the minnow and has alternating bluish-black and white stripes that run the length of its body. It is native to south Asia, tolerant of unclean water, and comfortable in temperatures from 61-93°F. Zebrafish are very social and travel in schools. Females can spawn every few days, laying hundreds of eggs at a time. The eggs hatch in 72 hours and the fish is sexually mature in three months. And zebrafish breed readily in captivity.
What I didn’t know then was how remarkable these creatures are, and why they make ideal research subjects. They share 70% of their DNA with humans — implying a common ancestor about 300 million years ago — and they are capable of episodic memory. That means they can recall objects, locations and incidents. Episodic memory is associated with conscious experience.
They are one of the few species of fishes that have been sent into space. They can regenerate heart cells, photoreceptors and retinal neurons after injuries. They can regrow lost fins. They can repair a damaged spinal cord without scarring. Research with zebrafish has contributed to advances in developmental biology, oncology, toxicology, reproductive studies, congenital abnormalities, genetics, neurobiology, environmental sciences, stem cell research, regenerative medicine, muscular dystrophies and evolutionary theory. A student at Georgetown University, my alma mater, is studying the brains of zebrafish that exhibit Autism Spectrum Disorder, hoping to learn more about how autism affects the human brain. Wow!
Immature zebrafish are completely transparent, which makes them perfect for studying cellular development. It also means that, as laboratory animals, they can be studied without being killed. There is a Zebrafish International Resource Center in Oregon and another in Germany. As for the zebrafish genome, by turning various genes on and off, scientists can form hypotheses about which human genes control which diseases and immune responses.
Dr. Derek Stemple, head of zebrafish genetics at the Sanger Institute says, “We are developing an enormously powerful tool this way, one that will pinpoint the functions of our all genes and help us create new medicines that can tackle diseases linked to those genes. And it is all happening thanks to the zebrafish.”
PS: Grammar lesson. The plural of fish is fish when you’re talking or writing about a single species. If more than one species is involved, the plural of fish is fishes.