Bimodal distribution of length of juvenile Atlantic salmon ( Salmo salar L.) under artificial rearing conditions

• Published in: Journal of Fish Biology
• Main Author: Thorpe, J. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1977
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1111/j.1095-8649.1977.tb04111.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1095-8649.1977.tb04111.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1095-8649.1977.tb04111.x

In 52 populations of juvenile Atlantic Salmon, Salmo salar L., from 14 pairings of wild parents, reared at the Almondbank smolt rearing station between 1973 and 1976 in circular radial‐flow tanks, bimodality in the frequency distribution of length and weight has been characteristic by the first autumn of growth, and has become progressively clearer during the following winter. The examination of 13 populations showed the modes did not correspond to separate sexes, from four others it was shown they did not correspond to immature fish and precociously mature males. It is suggested that the two modes correspond to subpopulations smoltifying at ages ( t ) and ( t +1) years. The age‐composition of the smolt‐run originating from individual year‐classes of salmon in four Scottish rivers was found to be consistent with stocks having size‐group segregations, at the time of the first smolt emigration, similar to those found among Almondbank experimental material. It is inferred that bimodality of size distribution is the norm among sibling populations of juvenile Atlantic salmon.