Is smolting a positive or a negative developmental decision?

• Published in: Aquaculture 1998-10, Vol.168 (1), p.95-103
• Main Authors: Thorpe, John E, Metcalfe, Neil B
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Animal and plant ecology; ANIMAL DEVELOPMENTAL STAGES; Animal migration; Animal, plant and microbial ecology; ANIMALES JOVENES; Animals; Atlantic salmon; Autoecology; Biological and medical sciences; ETAPAS DEL DESARROLLO ANIMAL; Fish; Food restriction; Freshwater; Fundamental and applied biological sciences. Psychology; JEUNE ANIMAL; MADURACION; Marine; Marine biology; MATURATION; Physical growth; SALMO SALAR; SALMON; SAUMON; Smolting; STADE DE DEVELOPPEMENT ANIMAL; Vertebrata; YOUNG ANIMALS
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/S0044-8486(98)00342-1

Salmonid life histories are characterised by the ages at which the two primary developmental conversions, smolting and sexual maturation, are made. For Atlantic salmon, the critical seasons at which the physiological decisions are taken are thought to be soon after midsummer for the smolting conversion, and in mid-autumn for the maturity conversion. Maturity is inhibited if genetically determined performance thresholds are not met. Experiments were designed to test whether smolting was controlled in a similar sense. Sibling upper modal growth group fish (mean wet weight 10.34±0.02 g) were divided into two replicated treatment groups on 11 February. One treatment group was fed a standard ration of 3% body weight/day until 1 June; the other group was fed this same ration but only during 1 week in four. All fishes had silvered by early May. On 11 May, when 96-h challenge tests in 35‰ artificial seawater were started, the mean weights of the unrestricted and restricted groups were 16.3±1.7 and 9.4±1.2 g, respectively. By 18 May all the unrestricted and 47.5% of the restricted groups survived the challenge. By 25 May, survival of the restricted group had increased to 65%. On 1 June only one fish from the unrestricted and none from the restricted group survived the transfer. Survival after transfer was related significantly to weight at transfer: larger smolts survived better than did smaller smolts ( p