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- Modulation of intestinal growth and differentiation by photoperiod and dietary treatment during smoltification in Atlantic salmon (Salmo salar, L.)Publication . Fernandes Duarte, Vilma Vanessa; Gaetano, Pasqualina; Striberny, Anja; Hazlerigg, David; Jørgensen, Even H.; Fuentes, Juan; Campinho, Marco AntónioAtlantic salmon undergo smoltification, a process that prepares the fish to enter and thrive in seawater (SW). Several physiological changes occur during smolting, especially in osmoregulatory tissues, the gill, the kidney, and the intestine. Here we characterized the effects on intestinal morphogenesis of two different, commonly used smoltification regimes during the end of the freshwater phase, photoperiod and/or the addition of salt and amino acid supplements in the diet. We focused on intestinal morphological differentiation, i.e., external perimeter, absorptive perimeter, tissue thickness, and villi density. In addition, we quantified cell proliferation (PCNA positive) and Na+, K+-ATPase (NKA) and Na+, K+,2Cl- (NKCCs) co-transporters expression and enterocyte apicobasal distribution by immunohistochemistry. These analyses show that the anterior and posterior intestines have different developmental dynamics during smoltification. In both intestinal regions, photoperiod and dietary treatment increased the absorptive perimeter. In addition, diet and photoperiod treatments differentially stimulated NKA protein expression in the anterior intestine. NKCC apical-basolateral expression in the enterocytes increased after SW entry in the anterior and posterior intestines. In conclusion, our results show that, as smoltification progresses, the anterior intestine responds more readily to experimental conditions than the posterior intestine. In our study, photoperiod and dietary treatment seem to enhance the development of the capacity to tolerate SW.
- Photoperiod and dietary treatment in freshwater modulate the short-term intestinal response to seawater in atlantic salmon (salmo salar)Publication . Gaetano, Pasqualina; Fernandes Duarte, Vilma Vanessa; Striberny, Anja; Hazlerigg, David; Jørgensen, Even H.; Campinho, Marco António; Fuentes, JuanStimulation and timing of smoltification are essential for successful Atlantic salmon (Salmo salar) aquaculture. This study investigated intestinal responses during dietary and photoperiod manipulation in freshwater (FW) and after a subsequent seven days residence in seawater (SW). "Small" and "large" Atlantic salmon parr (-40 g and -130 g respectively) were treated in FW for 12 weeks and thereafter transferred to SW for seven days. During the FW phase, fish underwent two different light conditions, 24 L:0D - 24 L ("LL-LL" groups) and 7 L:17D - 24 L ("SP-LL" groups) or fed with either regular feed ("LL-LL C" and "SP-LL C" groups) or feed enriched with a salt mix plus free tryptophan ("LL-LL + diet" and "SP-LL + diet" groups). We analyzed Na+/K+-ATPase (NKA) activity, tissue bioelectrical properties in Ussing chambers, and intestinal fluid composition. The NKA activity showed minor variations in relation to fish size, treatments, or intestinal region (anterior or posterior). Photoperiod modulated epithelial bioelectrical properties (Isc and Rt) of the anterior and posterior intestine, particularly transepithelial resistance (Rt). Pharmacological experiments, targeting apical Na+/K+/2Cl- (NKCC2) and Na+/ Cl (NCC) co-transporters revealed intestinal region-and water salinity-dependent effects. In addition, stimu-lation of the intracellular cAMP with forskolin and IBMX showed intestinal region-, water salinity, and treatment-dependence responses with clear functional specialization of the anterior and posterior intestine. The intestinal fluid composition reflected the ability to process ingested SW and showed little variation in large fish. In sum-mary, our data suggest a better pre-adaptation of the intestine during light-stimulated smoltification (SP-LL groups), and the combination of light and diet might give, in an industrial aquaculture setting, an advantage to smaller, but not larger smolts. Intestinal fluid composition in small fish can be used as an index of intestinal function and may act as a long-term performance proxy in SW Atlantic salmon.
- 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.