Reproductive Behaviour of Sea Trout (Salmo Trutta) - the Consequences of Sea-Ranching

Abstract

Abstract Reproductive behaviour and factors associated with male and female mating success were studied in sea trout (Salmo trutta) in a stream water aquarium, during three successive years. We compared a sea-ranched and a wild-produced strain, both of the same genetic origin. In general, dominant males courted females more often, spent more time on the spawnable areas, and had higher mating success than lower ranked males. Body mass explained about 18% of the males' position in the dominance hierarchy. Sea-ranched males, however, achieved on average fewer matings than wild ones. Wild males courted the nest-preparing females and chased away other males more frequently than did the sea-ranched males. Females were observed to be aggressive towards males, especially when the females were preparing a nest. The males that were more frequently the target of female aggression had smaller adipose fins and were more often aggressive towards females. In general the females spawned just once in each nest. Sea-ranched females defended and tested their redd less frequently than the wild females did. Digging activity by wild females diminished closer to spawning time, but not that of the sea-ranched females. To what extent the observed differences were due to the environmental conditions or to genetic differences is not known at present. However, the results of previous studies have revealed that behavioural and morphological differences exist between the strains, despite being reared under the same conditions. Thus, the behavioural changes noted in the sea-ranched sea-trout might have a genetic element.