Striberny A, Lysne H, Mikkelsen H, Teien H-C, Kristensen T, Rosseland B O, Stefansson S O, Salbu B, Toften Hilde
Nofima, Tromsø, Norway.
Skretting AS, Stavanger, Norway.
J Fish Biol. 2025 Jun 23. doi: 10.1111/jfb.70115.
Norwegian Atlantic salmon (Salmo salar L.) smolt production strategies are multifaceted. One strategy involves rearing in brackish water during the smoltification process, often in combination with relatively low specific water flow (SWF). Even though such practices are common, there is still a lack of scientific documentation of how this affects fish welfare and performance. In the present study, we examined the performance and susceptibility to winter ulcer in Atlantic salmon smolts (52 g) reared in flow-through systems, either in fresh water (FW, 0 ppt) or brackish water (BW, 13-14 ppt) at three different SWFs ranging from 0.27 to 0.12 L kg min for 6 weeks during smoltification (Phase 1). As SWF decreased, carbon dioxide (CO) levels increased and pH decreased in the rearing water. The fish were individually tagged and introduced to the different treatment regimens 120 degree-days after start of light induced smoltification. Subsequently, all treatment groups were transferred to seawater and subjected to an infection trial with Moritella viscosa or mock-infected (Phase 2). During the experimental period all groups developed typical smolt characteristics, including loss of parr marks and silvering, development of hypoosmoregulatory capacity and a decrease in condition factor. The different SWFs affected growth in both FW and BW groups. In Phase 1, growth was lower in the groups with the lowest SWF (p < 0.0001) and within these, the growth of fish in BW was significantly lower than of fish in FW. However, at moderate SWF levels, fish in BW grew better than fish in FW. No differences were found between the two groups with the highest SWF. In Phase 2, growth increased in all groups compared to Phase 1. Fish in the FW that had previously been subjected to the lowest SWF had significantly higher growth than those subjected to higher SWF; this was not the case in the BW groups. Blood chemistry analyses revealed increased partial pressure of CO (pCO) in the groups with lower SWF, irrespective of salinity (p < 0.0001). Both blood pCO and bicarbonate (HCO ) levels were positively correlated with increasing CO concentrations measured in the rearing water. Lower survival rates in the disease challenge test in the BW groups than in the FW groups indicate that premature exposure to higher salinities during smoltification may increase the susceptibility to M. viscosa. These results highlight that the use of a salinity around 14 ppt during smoltification does not alter growth when used in combination with a sufficient SWF, but make the fish less robust against a common bacterial pathogen.
挪威大西洋鲑（Salmo salar L.）的幼鲑生产策略是多方面的。一种策略是在幼鲑化过程中于半咸水中养殖，通常结合相对较低的单位水流量（SWF）。尽管这种做法很常见，但仍缺乏关于其如何影响鱼类健康和性能的科学文献记录。在本研究中，我们检查了在流水系统中养殖的大西洋鲑幼鲑（52克）在幼鲑化阶段（第1阶段）6周期间，于淡水（FW，0 ppt）或半咸水（BW，13 - 14 ppt）中，在三种不同的SWF（范围从0.27至0.12 L kg min）下的性能以及对冬季溃疡的易感性。随着SWF降低，养殖水中的二氧化碳（CO）水平升高且pH值降低。在光诱导幼鲑化开始120度日之后，对鱼进行个体标记并引入不同的处理方案。随后，所有处理组都转移到海水中，并进行了粘滑莫拉菌感染试验或假感染（第2阶段）。在实验期间，所有组都发育出典型的幼鲑特征，包括幼鲑斑纹消失和体表变银、低渗调节能力的发展以及肥满度下降。不同的SWF影响了FW组和BW组的生长。在第1阶段，SWF最低的组生长较慢（p < 0.0001），在这些组中，BW中的鱼生长明显低于FW中的鱼。然而，在中等SWF水平下，BW中的鱼比FW中的鱼生长得更好。SWF最高 的两组之间未发现差异。在第2阶段，与第1阶段相比，所有组的生长都增加了。先前处于最低SWF的FW中的鱼比处于较高SWF的鱼生长明显更高；BW组中情况并非如此。血液化学分析显示，SWF较低的组中二氧化碳分压（pCO）升高，与盐度无关（p < 0.0001）。血液pCO和碳酸氢盐（HCO）水平都与养殖水中测得的CO浓度升高呈正相关。BW组在疾病攻毒试验中的存活率低于FW组，这表明在幼鲑化期间过早暴露于较高盐度可能会增加对粘滑莫拉菌的易感性。这些结果表明，在幼鲑化期间使用约14 ppt的盐度并结合足够的SWF时不会改变生长，但会使鱼对常见细菌病原体的抵抗力降低。
