Regular in situ cleaning of net pens is performed to prevent overgrowth and negative effects of biofouling during the sea phase of salmon production in Norway. Possible negative health effects of in situ net cleaning include a reduction in appetite, increased stress, and gill damage. Gill lesions have been reported after exposure to Ectopleura larynx in laboratory trials, but there is currently little information available on whether exposure to biofouling debris from in situ net cleaning significantly contributes to development of gill disease and reduced gill health of farmed Atlantic salmon (Salmo salar) in sea cages. To assess this, gill tissue from healthy fish (n = 30 per pen/time point) from 3 net pens were collected before, as well as one and eight days after the first net cleaning event after sea transfer. The tissue was examined using a standardized histology scoring system. All fish originated from the same commercial sea site located in North-western Norway and net cleaning was performed as per routine for this site. The level of net fouling was scored using a semiquantitative scoring system ranging from 0 to 6, i.e., from totally clean to heavy fouling. Two pens were moderately fouled, and one had a low degree of fouling. The probability (odds) of fish from moderately fouled net pens having subacute vascular damage (thrombi) in the gills at one day after net cleaning was 2.36 (95% CI 1.21–5.71) times higher compared to fish sampled before net cleaning. When all fish were included in the statistical analysis no difference in the number of fish with the recorded lesions were found across the different sampling points and there was even a small decrease in the probability (odds) of fish having acute vascular lesions at eight days after net cleaning. Our results suggest that exposure to biofouling debris during net cleaning might contribute to development of thrombi/subacute vascular lesions in the gills. However, the proportion of gill tissue affected was low, generally estimated to be less than 1%, and no significant difference in the number of fish with these lesions was found at eight days after net cleaning. Thus, the negative impact of in situ net cleaning on gill health in this study is small and short lived, and the clinical implication of these results remains to be established.

在挪威鲑鱼生产的海上阶段，定期对网栏进行原位清洁，以防止过度生长和生物污垢的负面影响。原位净清洁可能对健康造成的负面影响包括食欲下降、压力增加和鳃损伤。在实验室试验中，已经报告了接触Ectopleura 喉后的鳃损伤，但目前几乎没有关于暴露于原位网清洁产生的生物污垢碎片是否会显着促进养殖大西洋鲑鱼（Salmo salar）鳃病的发展和鳃健康降低的信息。) 在海笼中。为了评估这一点，健康鱼的鳃组织 ( n = 30 每笔/时间点）从之前以及海上转移后第一次净清洁事件后的 1 天和 8 天收集的 3 个网栏。使用标准化的组织学评分系统检查组织。所有鱼都来自位于挪威西北部的同一个商业海域，并按照该地点的例行程序进行净网清洁。使用半定量评分系统对净污染水平进行评分，范围从 0 到 6，即，从完全清洁到严重污染。两支笔中度结垢，一个结垢程度较低。与清洁网前取样的鱼相比，在清洁网后一天，中度污染的网栏中的鱼在鳃中出现亚急性血管损伤（血栓）的概率（几率）是 2.36（95% CI 1.21–5.71）倍。当所有的鱼都包括在统计分析中时，没有发现不同采样点记录病变的鱼的数量存在差异，甚至在 8 天后出现急性血管病变的鱼的概率（几率）甚至略有下降净清洁。我们的结果表明，在净清洁过程中接触生物污垢碎片可能会导致鳃中血栓/亚急性血管病变的发展。然而，受影响的鳃组织比例很低，一般估计小于 1%，清洗网后 8 天发现有这些病变的鱼的数量没有显着差异。因此，负面影响在这项研究中，原位净清洁对鳃健康的影响很小且持续时间很短，这些结果的临床意义仍有待确定。