The effect of low temperatures and photoperiods on growth and vertebra morphometry in Atlantic salmon

Abstract

The aim of this study was to reveal possible interactive effects of temperature and photoperiod on somatic and skeletal growth, feed conversion, organ indexes and blood chemistry in Atlantic salmon postsmolts. A total of 1140 (initial mean weight 96.0 g ± 3.1 SEM) juvenile Atlantic salmon reared in seawater were in duplicates exposed to six different combinations of temperatures (4.3, 6.5 or 9.3°C) and photoperiods (continuous light, LL or simulated natural photoperiod (698N), LDN) for 124 days. An interactive effect of photoperiod and temperature on somatic growth was found as the fish exposed to low temperature and continuous light regime (4LL) had a significantly higher growth (30 % gain in overall SGR) than the 4LDN group, corresponding to the effect of approx. 1.2°C temperature increase. Fish in the 6 and 9°C groups did not show any significant growth benefit of continuous light. Compared to the 4LDN group, the 4LL group showed higher total feed conversion efficiency, lower levels of blood Na ? and lower hepatosomatic and cardio-somatic indexes. In the skeleton, cervical vertebra were largest in the 4LL group, while the length of the head was largest in the 4LDN group, continuous light promotes growth at lower temperatures while supporting a normal development. It is suggested that a considerable growth benefit may be achieved by exposing juvenile Atlantic salmon to continuous light when reared at low (in this trial 4.3°C) water temperature during winter.

Growing in the Dark Warmth: The Case of Amazonian Fish Colossoma macropomum

“…A growth-stimulating effect has been reported in continuous light at low temperatures for species such as Hippoglossus hippoglossus L. and S. salar (Jonassen et al, 2000;Lohne et al, 2012;Handeland et al, 2013). According to the findings of Døskeland et al (2016), the magnitude of these effects is inversely related to the increase in temperature indicating higher efficiency for animals raised at low temperatures when in continuous light, than at temperatures close to the optimum of the species. Even not testing a continuous light condition, the increase in the natural photoperiod found in nature by the species indicated the same effect in our study for tambaqui, although it was not accompanied by good indicators of food efficiency and body condition.…”

“…Seasonal and estuarine species have their growth rates controlled by seasonal changes resulting from increased photoperiod and environmental temperatures in the summer and spring. However, this pattern is not similar among species, since the potentiating effect of growth promoted by periods of prolonged or continuous light may become limited at elevated temperatures (Lohne et al, 2012;Døskeland et al, 2016). In natural environments, the photoperiod affects fish development, in addition to plankton productivity and migration, an important food source, and oxygen producer in these ecosystems.…”

“…The optimal temperature for growth in freshwater fish can be altered according to changes in the photoperiod (Coutant et al, 1984;Woiwode and Adelman, 1991). However, light also affects marine and temperate species, as showed by Døskeland et al (2016) for the Atlantic salmon Salmo salar L. Some studies have revealed limiting effects of continuous light at higher temperatures for growth, whereas at lower temperatures these effects appear to increase fish development (Solbakken et al, 1994;Imsland et al, 1995Imsland et al, , 2017Lohne et al, 2012). These studies suggest an interactive effect of photoperiod and temperature on fish growth.…”

Flesh quality of Atlantic salmon smolts reared at different temperatures and photoperiods

“…A detailed analysis of part of the growth data presented here was given by Døskeland et al (). An interactive effect of photoperiod and temperature on somatic growth was found as the fish exposed to low temperature and continuous light regime (4LL) had a significantly higher growth (30% gain in overall SGR) than the 4LDN group, corresponding to the effect of approx.…”

“…The experimental groups are abbreviated hereafter as 4LDN, 4LL, 6LDN, 6LL, 9LDN and 9LL. For more information about the background of the fish and experimental groups, see Døskeland et al ().…”