Day-degrees are not an absolute concept

KopiavInkubasjonstidberegning2_18670_image001The point in time for hatching of salmon eggs is often calculated to occur at 500 day-degrees after fertilization. This applies if the eggs have been incubated at between 6 and 8°C. However, in the course of a normal production cycle eggs are often stored at controlled temperatures of less than 6°C. This is sometimes necessary to deliver eggs according to the customers required point in time. Eggs which have been held at low temperatures i.e. below 6 °C will generally hatch with a day-degree sum of less than 500. (see the figure which shows the number of day-degrees from fertilization to hatching related to temperature. (based on Crisp, 1981)).

It is therefore important when estimating hatching time to know which temperature has been used before delivery and after stocking in the hatchery. The temperature regime prior to delivery can be found in the product information that accompanies all shipments. Responses from clients show that the eggs from Aqua Gen this season have hatched a little under 500 day-degrees, and the results from hatching and start feeding have been very good.