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

Abstract

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.

Photoperiod influence on the cultivation of Steindachneridion scriptum (Pisces, Pimelodidae) juvenile

“…For most of these species, the reduction of day length reduces the growth (McCormick et al, 1987, Stefansson et al, 1989, which can be observed in both freshwater (Saunders et al, 1985;Stefansson et al, 1989;Solbakken et al, 1994) and saltwater salmon (Saunders and Harmon, 1988;Krakenes et al, 1991;Hansen et al, 1992). …”

“…Several studies have been conducted on the influence of photoperiod on fish (McCormick et al, 1987;Krakenes et al, 1991;Bromage, 1995;Cerqueira and Brügger, 2001). Most of those studies were carried out with saltwater fishes or freshwater fishes from the northern hemisphere.…”

Evaluation of Seawater Adaptability of 0⁺ Japanese Char Related to Possibility of the Culture in Seawater

“…Therefore, the change of this enzyme activity is a good indicator of seawater adaptability and potential for growth in seawater. 4,[7][8][9] In the present seawater challenge test, gill Na+-K+AT In the seawater rearing test, no parr-smolt transforma tion was observed, indicating seawater adaptability of this fish is not always coincided with smoltification as de scribed previously,10-12) The gill Na+-K+ATPase activity at 103 days after seawater transfer increased up to 9 times, when compared with the initial value. Coinciding with the change of this enzyme activity, serum Na concentration decreased almost to the initial value.…”

The vitamin D receptor and its ligand 1α,25-dihydroxyvitamin D3 in Atlantic salmon (Salmo salar)

“…External stimuli like light trigger the smoltification process, and several hormones involved in the smoltification process (GH, PRL) have been identified (McCormick et al 1987). On the basis of this study calcitriol can be added to the list of hormones involved or taking part in the smollification process.…”