Environmental influences on growth, maturation and smoltification in Atlantic salmon parr, Salmo salar

• Main Author: Berrill, Iain Kevin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2003
• Subjects: Atlantic salmon; Aquatic ecology; Photoperiodism; Salmo salar
• Online Access: http://hdl.handle.net/1893/29192; http://dspace.stir.ac.uk/bitstream/1893/29192/1/Berrill.pdf

The maturation of Atlantic salmon (Safmo safar) parr, and its effects on growth and smoltification, causes significant economic losses to commercial aquaculture. The current thesis investigates the role of environmental factors on freshwater development, with the aim of providing information which would help reduce the currently observed levels of maturation in farmed salmon. The effects of short day "winter" photoperiods were investigated by exposing three replicated groups of fish to an 8 week "winter" photoperiod (LDlO:14) commencing in May, August or September, in an otherwise continuous light (LD24:0) regime. A further group was held on LD24:0 throughout. 200 to 300 individuals were PIT tagged in each group in order to follow the growth of fish undergoing different developmental strategies, with the retrospective analysis of such development also possible. The highest incidence of maturation (>20%) was observed in the May winter photoperiod group, with low levels recorded in the August and September fish «4%), suggesting that maturation may be influenced during a "critical" period in early development. Maturation levels were intermediate «9%) in the continuous light group indicating that seasonally-changing photoperiodic cues are not necessarily required for gonadal development. The size of mature fish was initially the same as both immature parr and smolts, although the growth of mature individuals subsequently declined, and at the conclusion of the experiment they were significantly smaller. The August photoperiod resulted in the highest incidence of smoltification, with all other treatments resulting in low levels. In a second experiment, PIT tagged fish were reared under an 8 or 12 week ''winter'' photoperiod (LD 10: 14) starting in Mayor June, in an otherwise continuous light (LD24:0) regime. The highest incidence of maturation (> 11 %) was found in the 12 week May fish, with intennediate levels in the 8 week May and 8 week June groups «8%). Low levels were found within the 12 week June group ...