Stress, cortisol, and feed intake in rainbow trout (Oncorhynchus mykiss) - Can you stomach the stress?

Fish in aquaculture is known to ingest less feed after exposure to stressors such as handling, crowding, vaccination and transportation. In scientific studies, this phenomenon has been ascribed to an appetite-reducing effect of stress, namely the stress hormone cortisol, or other aspects of the physiological stress response. However, preliminary findings have suggested that during recovery from stress fish has not necessarily lost the will to feed, but rather the ability to feed. To test the hypothesis that decreased feed intake in salmonids subjected to stressful situations is at least in part caused by other factors than a reduction in appetite, feed intake and attempts at feed intake in isolated rainbow trout was closely monitored after transfer to a novel environment. In a follow-up study known appetite markers were measured in the hypothalamus and plasma in rainbow trout receiving exogenous cortisol through feed. Furthermore, I also investigated alteration of the gastrointestinal (GI) tract in rainbow trout, by measuring stomach volume after exogenous cortisol exposure. From these studies I found that the anorectic stage following subjection to stress is, at least partly, mediated through some physical obstruction in the upper GI tract. I saw that nearly all fish went through three distinct phases of feeding behavior subsequent to stress exposure: Passive/anorectic, active but unable, and active and able. The second stage is an intermediate phase between being completely passive and successfully ingesting feed. The intermediate phase of feeding behavior has not been reported earlier. Here, fish are seen actively trying to ingest feed, but appearing unable to swallow, and thus repeatedly spitting grabbed pellets back out. I also noted that reduced feed intake in response to cortisol treatment was not caused by the alteration of neither corticotropin-releasing factor, cocaine- and amphetamine-regulated transcript, neuropeptide Y, leptin or arginine vasotocin, all which are known appetite-regulating factors. When examining stomach volume of rainbow trout intraperitoneally injected with cortisol, I found that stomach volume was significantly reduced compared to control. In conclusion, the sum of these findings indicates that the observed reduction of feed intake in stressed salmonids is not caused by the lack of appetite per se, but rather a physical obstruction somewhere along the upper GI tract, rendering the fish willing but unable to ingest feed. The mechanisms contributing to this behavior are still to be elucidated

Intensive smolt production is associated with deviating cardiac morphology in atlantic salmon

High pre-slaughter mortality rates of Atlantic salmon (Salmo salar L.) are a reoccurring welfare issue and economic burden in aquaculture. Sudden death immediately prior to slaughter is particularly problematic given the considerable resources invested to reach this stage. Although the underlying causes of such mortality are largely unknown, cardiac deformities and diseases have become increasingly prevalent observations in deceased fish. The factors leading to this pathology remains to be revealed. Thus, we presently examined if intensive smolt production and concordant fast growth rates in young fish is associated with altered cardiac morphology at later production stages in Atlantic salmon. The observed alterations were subsequently related to mortality risk following de-lousing in a facility with a cardiomyopathy syndrome (CMS) outbreak. We observed that intensive smolt production is indeed associated with slower growth rates at sea, distinct pathological cardiac morphological alterations, and expression of cardiac pathology markers. Moreover, the observed cardiac alterations co-occurred with CMS-related cardiac rupture at a different production facility. The present study demonstrates a clear link between pace of growth at early rearing stages and cardiac deformities later in life. Furthermore, these cardiac deformities are associated with cardiac rupture and mortality in individuals with CMS during delousing. We therefore believe that a slower pace of smolt production improves cardiac health and reduces the risk of mortality during CMS outbreaks.publishedVersio

Intensive smolt production is associated with deviating cardiac morphology in atlantic salmon

High pre-slaughter mortality rates of Atlantic salmon (Salmo salar L.) are a reoccurring welfare issue and economic burden in aquaculture. Sudden death immediately prior to slaughter is particularly problematic given the considerable resources invested to reach this stage. Although the underlying causes of such mortality are largely unknown, cardiac deformities and diseases have become increasingly prevalent observations in deceased fish. The factors leading to this pathology remains to be revealed. Thus, we presently examined if intensive smolt production and concordant fast growth rates in young fish is associated with altered cardiac morphology at later production stages in Atlantic salmon. The observed alterations were subsequently related to mortality risk following de-lousing in a facility with a cardiomyopathy syndrome (CMS) outbreak. We observed that intensive smolt production is indeed associated with slower growth rates at sea, distinct pathological cardiac morphological alterations, and expression of cardiac pathology markers. Moreover, the observed cardiac alterations co-occurred with CMS-related cardiac rupture at a different production facility. The present study demonstrates a clear link between pace of growth at early rearing stages and cardiac deformities later in life. Furthermore, these cardiac deformities are associated with cardiac rupture and mortality in individuals with CMS during delousing. We therefore believe that a slower pace of smolt production improves cardiac health and reduces the risk of mortality during CMS outbreaks