BY BETH GLIDEWELL, GENOA NATIONAL FISH HATCHERY
The Hine’s Emerald Dragonfly (HED) eggs that were housed at Genoa National Fish Hatchery over the winter began hatching in late March and by late May, 445 eggs had successfully hatched. These eggs arrived on station last November and were kept at cool, stable temperatures all winter. Eggs are kept by female line in sample cups of clean water and are checked frequently for fungal growth or other problems. Water is exchanged every other week to maintain good dissolved oxygen levels.
As temperatures began to warm outside this spring, we warmed the egg chamber slowly over several weeks and then above the critical hatching temperature of 42-43 °F. Cups are checked daily during the warming period for newly hatched larvae. As larvae hatch, they are pi petted out of the egg cup into their own specimen cup filled with about 20 milliliters of clean water of the same temperature water.
These new juvenile cups are allowed to slowly warm to room temperature in the mussel building, where they are fed zooplankton two to three times per week. Pond water that is pumped into the mussel building for fish housing and mussel culture is also filtered through a series of mesh screens, and zooplankton that are between 55 to 300 microns are retained, concentrated, and ‘fed’ or pipetted into each juvenile cup. This mixture of rotifers, cladocerans, copepods and other naturalized pond zooplankton make great Hine’s Emerald larvae food, and also feeds young of the year fish cultured in the various ponds at the hatchery.
The juvenile dragonflies will be housed in these cups until early to mid-June when they’ve (hopefully) grown large enough to be moved to screened cages or ‘s-cages’ that can be kept in larger, flow-through tanks in the dragonfly trailer all summer. Stay tuned for pictures and updates from this next stage of HED culture!
Above: HED eggs stored at stable temperatures over winter. The eggs are housed at about 39 degrees Farenheit from November to March. Credit: Beth Glidewell/USFWS