Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum (RS) is a chronic, often fatal disease of salmonid species, and can be particularly harmful to hatchery reared Chinook salmon (Oncorhynchus tshawytscha). Considerable research has focused on prevention of vertical and horizontal transmission; however, comparatively little research has investigated factors that increase prevalence of RS infection in captive environments. We evaluated the effects of three common hatchery conditions (handling, nutrition level, and rearing density), on RS infection prevalence. Fish were sampled at 30- and 60-days post-exposure to RS. Of 577 juveniles examined, 65 (11.27%) had anterior kidneys infected with RS. Using a logistic mixed model analysis, we found effects of nutrition level (P=0.018), handling (P=0.010) and sampling period (P=0.003) on the prevalence of RS. The interactions of nutrition and handling (P=0.008), and nutrition and time (P<0.001) were also significant. When fed a standard nutrition diet, proportionately fewer fish were infected with RS when not handled (7.16% vs 0.04%; P=0.003). Fish in the standard nutrition group also had a lower prevalence of RS during the second sampling period (4.08% vs 0.08%, respectively; P<0.001). When not handled, rearing with standard nutrition (11.50% vs 0.04%; P=0.004) resulted in a reduction in prevalence of RS infection. Additionally, non-handled fish had a much lower prevalence of RS infection during the second sampling period (2.66% vs 0.21%; P=0.009). While density did not affect prevalence of RS infection (P=0.145), fish reared at higher density had lower RS infection when not handled (16.48% vs 0.84%, p=0.004). For higher density fish, RS prevalence was lower during the second sampling period (10.57% vs 1.40%; P=0.002). Our results suggest that hatchery managers can reduce RS infection prevalence by maintaining an adequate nutritional regime as recommended by the manufacturer. Additionally, prevalence of RS may be reduced if managers decrease handling of hatchery-reared Chinook salmon if exposed to RS.

中文翻译：

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孵化场饲养密度、处理和营养对幼年奇努克鲑 ( Oncorhynchus tshawytscha ) 沙门氏菌感染率的影响

由鲑鱼肾杆菌 (RS) 引起的细菌性肾病 (BKD) 是鲑鱼属的一种慢性、通常致命的疾病，对孵化场饲养的奇努克鲑鱼 (Oncorhynchus tshawytscha) 尤其有害。大量研究集中在预防垂直和水平传播；然而，相对较少的研究调查了圈养环境中增加 RS 感染率的因素。我们评估了三种常见孵化场条件（处理、营养水平和饲养密度）对 RS 感染率的影响。在暴露于 RS 后 30 天和 60 天对鱼进行取样。在检查的 577 只幼鱼中，65 只 (11.27%) 的前肾感染了 RS。使用逻辑混合模型分析，我们发现营养水平 (P=0.018)、处理 (P=0.010) 和采样周期 (P=0. 003) 关于 RS 的流行。营养和处理（P=0.008）以及营养和时间（P<0.001）的相互作用也很显着。当喂食标准营养饮食时，未处理时感染 RS 的鱼按比例减少（7.16% 对 0.04%；P=0.003）。在第二次采样期间，标准营养组中的鱼的 RS 患病率也较低（分别为 4.08% 和 0.08%；P<0.001）。如果不处理，用标准营养饲养（11.50% 对 0.04%；P=0.004）导致 RS 感染率降低。此外，在第二个采样期间，未经处理的鱼的 RS 感染率要低得多（2.66% 对 0.21%；P=0.009）。虽然密度不影响 RS 感染的流行率 (P=0.145)，但在不处理时，以较高密度饲养的鱼的 RS 感染率较低（16.48% 对 0.84%，p=0.004）。对于密度较高的鱼，第二次采样期间 RS 流行率较低（10.57% 对 1.40%；P=0.002）。我们的结果表明，孵化场管理者可以通过维持制造商推荐的充足营养方案来降低 RS 感染率。此外，如果管理人员减少对暴露于 RS 的孵化场饲养的奇努克鲑鱼的处理，则 RS 的流行可能会降低。