Former president Jim Gauld was guest speaker at Ellon Probus Club on July 13.
Based on a life-time’s experience in fishery and fish disease work Jim concentrated his talk on brown trout and rainbow trout, both of which (along with Arctic Char) trace their lineage back to the last Ice Age.
Once it was learned how to delay maturation in trout egg using ice, European settlers wasted no time in introducing brown trout to foreign lands. This first shipment of trout (and salmon) eggs from UK to Australia took place in 1857 when journey time to Tasmania was 77 days. Brown trout are now found worldwide, excluding Antarctica, and in many instances have taken over the habitats of previous native species.
Jim went on to discuss what trout eat and what eats trout, several of which are regarded in UK as invasive species. Two trout predators, North American mink and American Signal crayfish, have resulted from escapes of animals originally imported for farming. Escaped rainbow trout have not established breeding populations in UK primarily due to farmed fish coming from specially selected non-breeding stocks.
Trout survival can also be affected by diseases such as bacterial and fungal infections and infestations by parasites like the freshwater fish louse (Argulus) and the tiny but lethal leach-like fluke Gyrodactylus. In recent years several rivers in Norway have been totally cleared using Rotenone to remove this fluke and it was emphasised that fishermen need to adhere to safety guidelines currently in place to keep Gyrodactylus out of UK waters.