Effects of photoperiod manipulation on growth and reproduction in Atlantic cod (Gadus morhua L.)
Sexual maturation during commercial culture of Atlantic cod (Gadus morhua L.) represents a significant production bottleneck restricting the profitability of the industry. Such problems in other species have traditionally been addressed by artificial manipulation of photoperiod cycles, however littl...
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| Other Authors: | , , , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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University of Stirling
2005
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| Subjects: | |
| Online Access: | http://hdl.handle.net/1893/109 http://dspace.stir.ac.uk/bitstream/1893/109/1/PhD%20Thesis%20A%20Davie.pdf |
| Summary: | Sexual maturation during commercial culture of Atlantic cod (Gadus morhua L.) represents a significant production bottleneck restricting the profitability of the industry. Such problems in other species have traditionally been addressed by artificial manipulation of photoperiod cycles, however little research exists in this field in cod. This thesis therefore investigates the interactions between artificial photoperiod manipulation, sexual maturation and somatic growth in this species. In the first experiment, populations of Atlantic cod (hatched, spring 1999) were maintained on either a simulated natural photoperiod (SNP) or continuous illumination (LL) from approximately 15 months post hatch (MPH) (July 2000) in an enclosed tank system. Growth performance was recorded monthly along with observations of reproductive activity over the subsequent 2 years (up to July 2002). At both 2 and 3 years of age the entire population raised under SNP matured and spawned, during which time mean weight reduced by 13% and 24% respectively. No spawning individuals were recorded at 2 years of age in the LL population and only 18% were observed to spawn at 3. However, observations of both changes in gonadal morphology (observed via ultrasound scanning) and a suppression in growth rate at 2 years of age in the LL population alluded to a maturation “dummy run” regulated by an endogenous clock. Despite this phenomenon, the LL treatment realised a 39% and 43% improvement in wet weight following 1 and 2 years of exposure to LL respectively. When the diel cycle of plasma melatonin was compared between the treatments in February 2001 (23MPH) the SNP population displayed an A-profile diel rhythm ranging between 20 and 50 pg/ml while the LL treatment did not display any rhythm. In the second experiment of this work, two populations of cod (hatched, spring 2001) were reared in commercial open cage systems, one of which experienced continuous additional artificial illumination between July 2002 (15MPH) and October 2003 (30MPH) provided by ... |
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