ISSN:
1365-2109
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Two experiments were performed to study the relative significance of the absolute daylength and the change in photoperiod on the growth and development of bimodality in juvenile Atlantic salmon Salmo salar L. In Experiment A juveniles were reared on 24 h daily light until they were seven months old (65–82 mm in length after size grading). They were then divided into six groups and subjected to six photoperiods (6, 9, 12, 15, 18 and 24 h of light). In Experiment B the decrease in photoperiod was made in two steps. First, the day length was reduced to 18 and 21 hours, three months after first feeding when the weight of the juveniles averaged 2.5 g and one group was kept under 24 hour daily light. Two months later, each of these treatment groups was subdivided to produce new groups of juveniles (65–82 mm in length) under 6, 9 and 12 h of daily light. Irrespective of whether the photoperiods were reduced in one or two steps, groups held under short-day photoperiods, 6–12 h, grew significantly slower (Exp. A) and showed higher proportions of lower modal group fish (Exp. B) than groups treated with long-day photoperiods, greater than 12 h. There were low proportions of lower modal group fish among juveniles larger than 75 mm at the dates of decreases in daylength irrespective of photoperiod (Exp. B, 0–16%), and high or variable proportions among fish smaller than 75 mm, depending on photoperiod (Exp B. 32–71%). It is concluded that the growth response of juvenile Atlantic salmon changes in the range of 12–15 hours of daily light. This mechanism is probably linked to the size of the parr and is one important reason for the development of bimodal length-frequency distributions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2109.1997.00827.x
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