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- More than one way to smoltify a salmon? Effects of dietary and light treatment on smolt development and seawater growth performance in Atlantic salmonPublication . Striberny, Anja; Lauritzen, Daniel E.; Fuentes, Juan; Campinho, Marco António; Gaetano, Pasqualina; Duarte, Vilma; Hazlerigg, David G.; Jorgensen, Even H.Post-smolt mortality and stunted growth is a problem in Norwegian salmon farming that can be partly traced back to sub-optimal smolt quality in connection with ongoing changes in smolt production practices. In the present study, we compared smolt development and post-smolt performance in seawater (SW) of Atlantic salmon subjected to 1) traditional light treatment (short photoperiod (SP) long photoperiod (LL)), 2) a dietary treatment alone (LL-LL + diet), 3) a combination of light and diet (SP-LL + diet) treatment and 4) no stimulation (LL-LL control) during the freshwater (FW) phase. The transition diet consisted of feed supplemented with a salt mixture and the amino acid tryptophan. Effects of light and dietary treatment were tested on two different size classes (40 and 130 g) of parr. Response patterns to treatments were independent of initial size and findings discussed below apply to both. Fish in the continuous light groups (LL-LL and LL-LL + diet) had the highest mass gain during the FW phase while light treated fish had a reduction in condition factor indicative of a true smolting. Hypoosmoregulatory ability in May was increased by diet, but not by light. However, a strong and treatment independent decrease in gill NKA alpha 1a gene expression indicated a complete shift from a FWto a SW type gill Na+, K+-ATPase. Moreover, plasma Cl- concentration and osmolality after 7 days in SW in May were well within the range expected for fully SW adapted fish in all treatment groups. Despite good hypoosmoregulatory abilities in all fish, there were strong treatment dependent effects on their growth during the two month SW residence. SW growth was negatively correlated with growth and change in K during the last part of the FW phase. A markedly higher specific growth rate and appetite in the SP-LL group than in the LL-LL group was likely a result of the light stimulated endocrine changes that occurred during smolting. Dietary treatment seemed to compensate for the lack of light treatment since feed intake and growth in LL-LL + diet fish was comparable to that in the SP-LL treated smolts. Feed intake and growth in the SP-LL + diet groups was highest, giving support for a notion that light and diet act through separate and additive mechanisms.
- Molecular responses in the intestine of Atlantic salmon (Salmo salar) following light and diet stimulation of smoltification: Potential molecular markers for a seawater-ready smoltPublication . Gaetano, Pasqualina; Fernandes Duarte, Vilma Vanessa; Striberny, Anja; Hazlerigg, David G.; Jørgensen, Even H.; Campinho, Marco António; Fuentes, JuanThe transfer to seawater (SW) represents a critical stage in the production of Atlantic salmon. The success of the transfer links with the optimal development of hypo-osmoregulatory capacities during smoltification. While various strategies are adopted in aquaculture to stimulate smoltification, considerable fish loss still occurs after transfer to sea cages. Therefore, we investigated the molecular responses in the anterior and posterior intestine of Atlantic salmon, following 1) a photoperiod treatment (24 h light (L):0 h dark (D) → 24 L:0D vs. 7 L:17D → 24 L:0D) and 2) dietary treatment (regular feed or feed enriched with a salt mix/tryptophan), combined with, or without a photoperiodic treatment in freshwater (FW), to evaluate how intestinal osmoregulatory mechanisms are modulated by these treatments, and to identify potential intestinal markers indicative of a SW-ready smolt. Using quantitative real-time PCR (qPCR), we investigated transcript levels of transporters and channels involved in ion movements through the enterocytes, tight junction components, and receptors (i.e., calcium-sensing re ceptor and prolactin receptor). The two intestinal regions showed different gene profiles and responsiveness towards the experimental treatments. In the anterior intestine, the exposure to short photoperiod (7 L:17D) upregulated Na+/K+ − ATPase subunit alpha 1c (nkaα1c), Na+/K+/2Cl− cotransporter 1 (nkcc1), Na+/K+/2Cl− cotransporter 2 (nkcc2), Cl− /HCO− 3 exchanger Slc26a6 (slc26a6), and cystic fibrosis transmembrane conductance regulator I (cftrI), in FW and SW. Also, Na+/K+ − ATPase subunit alpha 1b (nkaα1b), occludin (ocln), and prolactin receptor (prlr) were upregulated in FW and claudin 15 (cldn15) in SW groups exposed to this photo period. The posterior intestine was less responsive to the experimental treatments, although upregulation of nkcc1, nkcc2, slc26a6, and cftrI was observed in FW in the short photoperiod groups. Hence, our findings show that exposure to a winter signal in FW more effectively activates hypo-osmoregulatory mechanisms in the in testine of Atlantic salmon, where a coordinated and complementary role of the anterior and posterior intestine ensures optimal SW processing. Dietary treatment had a positive but more marginal effect on the regulation of the genes investigated, mainly enhancing the impact of short photoperiod when the two treatments were combined. Overall, we propose the apical Na+/K+/2Cl− cotransporter, nkcc2, and the apical Cl− / HCO− 3 exchanger, slc26a6, as potential FW molecular markers in the anterior intestine to assess “SW-readiness” in Atlantic salmon smolts.
- Molecular responses in the intestine of Atlantic Salmon (Salmo salar) following light and diet stimulation of smoltification: Potential molecular markers for a seawater-ready smoltPublication . Gaetano, Pasqualina; Fernandes Duarte, Vilma Vanessa; Striberny, Anja; Hazlerigg, David G.; Jørgensen, Even H.; Campinho, Marco António; Fuentes, JuanThe transfer to seawater (SW) represents a critical stage in the production of Atlantic salmon. The success of the transfer links with the optimal development of hypo-osmoregulatory capacities during smoltification. While various strategies are adopted in aquaculture to stimulate smoltification, considerable fish loss still occurs after transfer to sea cages. Therefore, we investigated the molecular responses in the anterior and posterior intestine of Atlantic salmon, following 1) a photoperiod treatment (24 h light (L):0 h dark (D) -* 24 L:0D vs. 7 L:17D -* 24 L:0D) and 2) dietary treatment (regular feed or feed enriched with a salt mix/tryptophan), combined with, or without a photoperiodic treatment in freshwater (FW), to evaluate how intestinal osmoregulatory mechanisms are modulated by these treatments, and to identify potential intestinal markers indicative of a SW-ready smolt. Using quantitative real-time PCR (qPCR), we investigated transcript levels of transporters and channels involved in ion movements through the enterocytes, tight junction components, and receptors (i.e., calcium-sensing receptor and prolactin receptor). The two intestinal regions showed different gene profiles and responsiveness towards the experimental treatments. In the anterior intestine, the exposure to short photoperiod (7 L:17D) upregulated Na+/K+ - ATPase subunit alpha 1c (nka alpha 1c), Na+/K+/2Cl- cotransporter 1 (nkcc1), Na+/K+/2Clcotransporter 2 (nkcc2), Cl- /HCO-3 exchanger Slc26a6 (slc26a6), and cystic fibrosis transmembrane conductance regulator I (cftrI), in FW and SW. Also, Na+/K+ - ATPase subunit alpha 1b (nka alpha 1b), occludin (ocln), and prolactin receptor (prlr) were upregulated in FW and claudin 15 (cldn15) in SW groups exposed to this photoperiod. The posterior intestine was less responsive to the experimental treatments, although upregulation of nkcc1, nkcc2, slc26a6, and cftrI was observed in FW in the short photoperiod groups. Hence, our findings show that exposure to a winter signal in FW more effectively activates hypo-osmoregulatory mechanisms in the intestine of Atlantic salmon, where a coordinated and complementary role of the anterior and posterior intestine ensures optimal SW processing. Dietary treatment had a positive but more marginal effect on the regulation of the genes investigated, mainly enhancing the impact of short photoperiod when the two treatments were combined. Overall, we propose the apical Na+/K+/2Cl- cotransporter, nkcc2, and the apical Cl- / HCO-3 exchanger, slc26a6, as potential FW molecular markers in the anterior intestine to assess "SW-readiness" in Atlantic salmon smolts.