EFFECTS OF OVERRIPENING ON SPAWNING BEHAVIOR AND REPRODUCTIVE SUCCESSOF ATLANTIC SALMON FEMALES SPAWNING IN A CONTROLLED FLOW CHANNEL

The influence of overripening on salmonid egg quality has often been d escribed in artificial breeding. However, no information exists on the impact of this factor on fish reproducing naturally, although it is l ikely to be critical, especially in disturbed environments. Pairs of A tlantic salmon in which the size of the male and the female was evenly matched were released in a spawning channel from 1 to 12 days after o vulation. Handling, did not affect egg quality. Overripening had a neg ative effect on egg viability. Egg mortality, infertility and malforma tions increased with the number of days after ovulation. In females wh ich had just matured, 16.7% of their recovered eggs were dead, 3.1% we re unfertilized and 1.7% were malformed, as compared to 25.4, 9.7 and 5.4%, respectively, in females that had been mature for at least a wee k. Overripening played a role in both female spawning behaviour and ca pacity to spawn, as females which had been mature for over a week rele ased their eggs more quickly while they retained more ova in their abd ominal cavity than early spawning females. Thus, in studies of reprodu ctive behaviour and in particular of sexual selection, it is critical to take into account the maturation status of females since the durati on of spawning activity is used by various authors to determine female sexual motivation. Alternatively, overripening may decrease the femal e selectivity for mates. (C) 1998 The Fisheries Society of the British Isles.