Growth of salmonids: eggs and fry

Egg Growth Help: Parameters for modeling growth

a1, a2, b1, b2

Temperature affects both the rate and efficiency of food utilization through the parameters a and b , which are the terms for anabolism and catbolism. a1, a2, b1 and b2 in this web formulation determine the exact relationship of anabolism and catbolism to temperature. It is unlikely you will need to change these for chinook salmon since the model was calibrated for chinook. However, other species may have very different relationships and the calibration process exists solely to determine these four parameters.


These are consistent with the Arrhenius relationship between temperature and reaction rates of molecular processes (Atkins 1994) and the basis for Q 10 values applied to cellular processes and to fish in particular following Winberg (1956).

c1, c2

Water absorption coefficients for the embryo pre and post hatch. The number represents the true absorbed mass as a proportion of the amount of yolk absorbed. Before hatching, only gas passes the egg shell, so c1 = 1. After hatching, the fish absorbs water along with nutrients. This parameter is calibrate like a1, a2, b1 and b2.

bhat, chat, khat

Prior to hatching, pre-hatch development rates must be calculated by the log-inverse Belehrádek model (Alderice and Velsen 1978) because hatching is a physiological stage that this model can not recognize. The proportion of pre-hatching development that occurs each day is:

These parameters are simply postpended with "hat" to be clear that they are hatching parameters. T is the temperature in Celsius on that day. Hatching occurs at time t when:

dyolk, dfish

Densities of egg and fish.


Time step size in days.

embryo, egg

Masses of these two entities (mg) when the egg is fertilized.


Fraction of the egg that is shell material.


The julian day of the year that the fish is spawned. Note that this is significant if the temperatures vary seasonally, otherwise it will have no effect at all.