Effects of continuous light and short-day photoperiod on smolting, seawater survival and growth in Atlantic salmon (Salmo salar)

Potential 1+ smolts of Atlantic salmon (Salmo salar) were reared under three light regimes: simulated natural photoperiod (LDN), continuous light (LD24:0), or a combination of continuous, low-intensity background light and a superimposed simulated natural photoperiod (dual photoperiod, LDD). Growth rate in freshwater was enhanced by LD24:0 and LDD, and changes associated with smoking (increased salinity tolerance, reduced condition coefficient) were advanced under LD24:0. Plasma growth hormone levels were initially high on LD24:0 and LDD whereas on LDN, plasma growth hormone levels increased gradually from February through April. Overall GH levels were negatively correlated with condition coefficient during the final stages of smoking. After 16 mo in seawater, there were no significant size differences among the groups. The incidence of sexual maturation as postsmolts was higher in the LD24:0 and LDD groups whereas the incidence of grilsing was higher in LDN. Results demonstrate the significant influence of photoperiod on growth and smoking in Atlantic salmon. An abrupt increase to continuous light in winter may be sufficient to advance important aspects of the parr–smolt transformation. Dual photoperiod may be a way to combine the increased growth rate observed under continuous light and the normal parr–smolt transformation associated with natural photoperiod.

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Photoperiod Control of Parr–Smolt Transformation in Atlantic Salmon (Salmo salar): Changes in Salinity Tolerance, Gill Na+,K+-ATPase Activity, and Plasma Thyroid Hormones

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f87-175 ◽

1987 ◽

Vol 44 (8) ◽

pp. 1462-1468 ◽

Cited By ~ 144

Author(s):

Stephen D. McCormick ◽

Richard L. Saunders ◽

Eugene B. Henderson ◽

Paul R. Harmon

Keyword(s):

Atlantic Salmon ◽

Thyroid Hormones ◽

Atpase Activity ◽

Salmo Salar ◽

Salinity Tolerance ◽

Continuous Light ◽

Day Length ◽

Atlantic Salmon Salmo Salar ◽

First Feeding ◽

Photoperiod Control

Atlantic salmon (Salmo salar) were subjected to artificial photoperiods to determine the manner and extent of photoperiod control of the parr–smolt transformation. Exposure to continuous light (L24) at first feeding and maintained throughout the rearing period inhibited increases in salinity tolerance and gill Na+,K+-ATPase activity that occurred in spring in fish raised under simulated natural photoperiod (SNP). Fish reared under continuous light and returned to SNP in October (L24OCT) underwent normal increases in salinity tolerance and gill Na+,K+-ATPase activity, whereas those returned in December (L24DEC) underwent delayed and intermediate increases. Plasma thyroxine peaks occurred simultaneously in all groups but were diminished in the L24 and L24DEC groups. Plasma 3,5,3′-triiodo-L-thyronine levels were not affected by any photoperiod treatment. Inhibition of the parr–smolt transformation decreased the potential for growth in seawater. In spite of changes in the timing of the transformation induced by photoperiod treatment, salinity tolerance and gill Na+,K+-ATPase activity were strongly correlated; correlation between changes in salinity tolerance and plasma thyroid hormones were, by comparison, weak. The results demonstrate that continuous light applied early in ontogeny and maintained throughout the rearing period inhibits osmoregulatory changes associated with parr–smolt transformation, whereas increasing day length during winter–spring stimulates transformation.

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Development of salinity tolerance in underyearling smolts of Atlantic salmon (Salmo salar) reared under different photoperiods

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f95-024 ◽

1995 ◽

Vol 52 (2) ◽

pp. 243-251 ◽

Cited By ~ 59

Author(s):

Åse I. Berge ◽

Arne Berg ◽

Trygg Barnung ◽

Tom Hansen ◽

Hans Jørgen Fyhn ◽

...

Keyword(s):

Atlantic Salmon ◽

Atpase Activity ◽

Salmo Salar ◽

Salinity Tolerance ◽

Continuous Light ◽

Short Photoperiod ◽

Subsequent Reduction ◽

Atlantic Salmon Salmo Salar ◽

First Feeding ◽

Natural Photoperiod

Groups of Atlantic salmon (Salmo salar), first fed in mid-February 1989, were reared under continuous light (LL) at 12–15 °C until late June. One group remained on LL, while the FEB, MAR, and MAY groups were subjected to segments of a simulated naturally increasing photoperiod (61°N), with initial daylength corresponding to February 1, March 15, and May 1, respectively. The MAR and FEB groups developed important smolt characters (increase in gill Na+,K+-ATPase activity, hypoosmoregulatory ability, and salinity tolerance) during the experiment whereas LL and MAY groups showed only incomplete changes in smolt status. The combination of continuous light during first feeding and early parr stages with a subsequent reduction to short daylength followed by a segment of simulated natural photoperiod allow important parts of the parr–smolt transformation to be completed. The period of exposure to short photoperiod is critical for the synchronization of smolt characters in underyearling Atlantic salmon.

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