This study imposed stress upon spawning cod Gadus morhua in the laboratory
to evaluate the potential effects of trawl avoidance on their reproductive
physiology and spawning behaviour. Plasma cortisol levels of stressed fish
were significantly higher than controls. Stressed cod initiated fewer court
ships and often performed an altered courtship sequence. Both control and s
tressed fish spawned and there was little difference in the production of e
ggs, fertilization rate, hatching success or time to starvation of larvae.
However, stressed fish produced abnormal larvae more frequently. Cod expose
d to a chronic stressor are able to spawn successfully, but there appears t
o be a negative impact of this stress on their reproductive output, particu
larly through the production of abnormal larvae. (C) 1999 The Fisheries Soc
iety of the British Isles.