#LabHacks: The egg harvesting helper
The heavy lab door swings open, revealing almost ceiling-high shelves on both sides. The room is tightly packed with aquariums teeming with life. Some 24,000 zebrafish of all ages are swimming around in the tanks. These small vertebrates, which are known for their distinctive horizontal stripes, are bred in the MDC’s own fish facility.
From mating to laying in just a few minutes
Robby Fechner, aquatic animal care manager at the MDC, looks after the fish facility’s five recirculating water systems as part of his work. He is also responsible for breeding the zebrafish. One of the key utensils for this is a tea strainer. “We use it to harvest the eggs,” Fechner says.
When the time comes to mate selected zebrafish, he puts the fish in special boxes in the evening. These boxes have a mesh base and removable partition walls. The next morning at 8 a.m., the light inside the fish facility turns on automatically. As soon as the transparent partitions are removed from the spawning boxes, the fish can begin mating. It takes just a few minutes for them to spawn. The fertilized eggs fall through the mesh at the bottom and are protected from the parent fish, which would otherwise gobble up their offspring. Fechner will wait until noon before he returns to the boxes, tea strainer in hand.
First, he puts the zebrafish back in their “home tank.” Then he empties out the water and fish spawn through the tea strainer. He thoroughly cleans the freshly laid 100 to 500 fish eggs with water from the aquarium’s recirculating system, rinsing them in a Petri dish containing water with methylene blue dye. “We use it to prevent fungal infection if the eggs die off,” Robby Fechner explains. The mortality rates vary enormously. With young parent fish, they can be as low as 0 percent, while with very old fish, sometimes not a single egg survives. Other factors, such as water parameters or light, play a crucial role.
The mini zebrafish are hatched in an incubator
The next stop for the eggs is the incubator, a converted refrigerator, set to a constant temperature of 28.5 degrees Celsius – the ideal temperature for zebrafish eggs to develop. They are incubated for five days, and when they are hatched, the tiny little fish are ready to go into the aquarium water. Another five days pass before they are large enough to move to “proper” aquariums, which are connected to the water system. It won’t be long before these fish lay eggs, too: zebrafish become sexually mature at 12 to 16 weeks.
Images: Editiorial team, MDC
