Environmental Regulation of Smolting and Maturation in Atlantic Salmon (Salmo salar L.) Parr

• Main Author: Adams, Colin Ean
• Format: Thesis
• Language: English
• Published: ProQuest Dissertations & Theses 1988
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://theses.gla.ac.uk/77652/; http://theses.gla.ac.uk/77652/1/10997924.pdf

Fish successfully exploiting rapidly changing environments must be capable of short-term adjustments to their life history strategy. Such a fish is the Atlantic salmon (Salmo salar L.). Salmon developmental rates (growth, smolting and sexual maturation) vary greatly between populations and families and are known to be heritable. However expression of genetically controlled developmental rate may be modified by environmental conditions. Thorpe in 1986 published a model linking parr growth, smolting and maturation rates. The model predicts that parr during their first year may be twice faced with distinct developmental pathway options, of which there are 3 phenotypic outcomes: sexually mature parr, capable of breeding during the following winter; immature parr which shut down growth over winter and appear as the lower mode of a bimodal size distribution in late autumn and do not emigrate to sea the following spring; smolts, which continue growth into their first winter, appearing as the upper mode in a bimodal size frequency distribution in autumn and emigrate to sea the following spring. The model predicts that the decisions are made during two discrete periods and these are temporally separate and that the developmental outcome of each is dependent on the rate of acquisition of energy during these periods. To test these predictions, sibling populations of underyearling parr, hatched early using heated incubation water and hatched at ambient water temperature, were exposed to simulated natural photoperiod regimes out-of-phase with controls (up to +3 months) and elevated water temperatures (up to 5