Comparisons of annual gonad cycle and fecundity between nominate and deepwater forms of vendace ( Coregonus albula L.) in Lake Stechlin (State of Brandenburg, Germany)

Summary Comparative studies on the reproductive biology of both forms (nominate and deepwater) of Coregonus albula L. in Lake Stechlin revealed the following results: Nominate and deepwater forms differed concerning their annual gonad cycle. Spawning in the nominate form is in early December, spawning in the deepwater form is from April to May. Apart from maturation stage V there were no differences in gonadosomatic indices (GSI) in either form at all maturation stages. The ratio between gonads and overall bodyweight for fish from maturation stages II‐IV and VI was similar in both forms; the only difference was found in females ready to spawn. The gonad mass in the nominate form was greater than that of the deepwater form. Differences existed between both forms in absolute and relative fecundity (number of eggs). Females from the nominate form were more fertile than those of the deepwater form. A positive correlation was found between body length and number of eggs; the same applied to the age of spawners and the number of eggs. Within the period of research, the sex ratio was different in both forms of vendace. Whereas a balanced sex ratio could be observed with regard to the deepwater form, there was a surplus of females in all samples of the nominate form.