A quick trip to the hatchery this morning as Jimmy Woods the hatchery manager said there was a good hatch underway. The water temp was a steady 4 degrees C and although a few of the eggs had hatched over the last two weeks today was the first significant hatch.
Very few eggs had hatched in the first tank (can’t remember which stock it held) but Jimmy said the eggs had elongated and were miss-shaped, a sure sign that the hatch was imminent.
The Sandbank hatchery uses hexhatch trays which revolve slowly with the water flow. Each tray can hold a lot of eggs, up to 100,000 in a commercial environment.
Once they hatch the little alevins fall through the egg tray into a lower compartment.
Once the hatch is complete Jimmy shifts the alevins into the incubators which are located adjacent to each tank. They remain in the incubator until the yolk sac is almost absorbed and they are ready to feed.
The incubator in an clever arrangement to simulate the conditons found in a natural redd in the gravel. The water flows in from the bottom, through a gauze and a layer of pea gravel. The incubator is then filled with plastic shapes to provide resting areas where the alevins can remain relatively immobile during the absorption of the yolk sac. Once the alevins have absorbed the yolk sac they self release into the tank at the optimum time for feeding. The credit for the incubator idea is I think due to Peter Gray, ex Keilder hatchery.
The Dulnain and Avon stock were stripped first and they were the first to hatch. It has been 125 days since the bulk of the Dulnain fish were stripped. Few of the Fiddich stock have hatched yet but they were stripped two weeks later. Jimmy records the water temperature daily but we also have a temperature logger in the intake which I’ll download later. I reckon it takes about 450 degree days for the eggs to hatch; 125 days at an average of 3.6 degrees C, that sounds about right. Almost the same again before they are ready for feeding.
There are about 230,000 eggs in the hatchery and the mortality rate to date has been less than 2%. The fish are destined for mitigation stocking in burns where there are man made barriers to fish passage.
Jimmy is a great observer of detail in the hatchery. He was pointing out the bubbles on the water surface of the tanks where a lot of fish had hatched. This was due he said to the empty egg shells breaking down. Interesting how the egg shells are stable whilst intact but break down so readily once they hatch. When he was showing me the incubators he pointed out the bits of detritus stirred up from the bottom. The alevins can be seen feeding on these particles just before they appear in the tanks. If you are going to have a hatchery you may as well have a good one!