Abstract:
Proliferative kidney disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae, is suspected to contribute to the decline of wild brown trout Salmo trutta populations. Different factors need to be taken into consideration for PKD outbreaks. Among them, water temperature appears as a main driver of the disease. To understand the epidemiology and impact of the disease on wild fish populations, reliable sampling approaches to detect the presence of T. bryosalmonae-infected fish are needed. This study aimed to characterize the seasonal variation of the prevalence of T. bryosalmonae-infected fish in brown trout populations in two small streams with differing temperature regimes between upstream and downstream sites. As water temperature is known to influence PKD manifestation in brown trout, we hypothesized that the number of T. bryosalmonae-positive fish, as well as their seasonal distribution, will vary between upper and downstream parts of the two streams. Since, in field studies, results can strongly vary across years, we extended the study over a 3-year-period. The number of infected fish and the intensity of infection were assessed by histology. The results confirmed the hypothesis of pronounced temporal- and site-related differences in the percentage of PKD-positive fish and the intensity of the infection. Comparison of water temperatures (total degree days as well as the number of days with a daily mean temperature ≥15 °C) with PKD data indicated that temperature was the driving factor for the temporal development and the intensity of the infection. A mean of 1500 degree days or 30 days with a daily mean temperature ≥15 °C was required before the infection could be detected histologically. From our findings, recommendations are derived for a water temperature-driven sampling strategy campaigns that enables the detection of PKD infection and prevalence in wild brown trout populations.
摘要:
增殖性肾脏疾病(PKD),由粘液虫寄生虫苔藓四爪虫引起,怀疑是导致野生褐鳟鱼Salmotrutta种群数量下降的原因。PKD爆发需要考虑不同的因素。其中,水温似乎是疾病的主要驱动因素。了解该疾病的流行病学和对野生鱼类种群的影响,需要可靠的采样方法来检测苔藓沙门氏菌感染的鱼类的存在。这项研究旨在表征在上游和下游站点之间温度状况不同的两个小溪中,褐鳟鱼种群中被苔藓感染的鱼类的流行率的季节性变化。由于已知水温会影响褐鳟鱼的PKD表现,我们假设苔藓沙门氏菌阳性鱼群的数量,以及它们的季节性分布,将在两个流的上部和下游部分之间变化。因为,在实地研究中,结果可能因年份而异,我们将研究延长了3年.通过组织学评估感染的鱼的数量和感染的强度。结果证实了PKD阳性鱼的百分比和感染强度的明显时间和部位相关差异的假设。水温(总度日以及日平均温度≥15°C的天数)与PKD数据的比较表明,温度是时间发展和感染强度的驱动因素。在组织学上检测到感染之前,需要平均1500度或30天的日平均温度≥15°C。根据我们的发现,针对水温驱动的采样策略活动提出了建议,该活动可以检测野生褐鳟鱼种群中的PKD感染和患病率。