Stress and disease resilience differences related to emergence time for first feeding in farmed rainbow trout (Oncorhynchus mykiss)

Abstract

Salmonid individuals show a relatively high variability in the time required to abandon the gravel nest where they hatch, the so-called 'emergence time'. Different behavioral and physiological traits have been shown to be associated with emergence time in wild salmonids. In general, early- and late-emerging fish have traits resembling those of proactive and reactive stress coping styles, respectively. Proactive fish are considered to be more resilient to stress and probably to disease, so it was hypothesized that fish with different emergence times have different abilities to resist repeated episodes of stress without suffering deleterious effects on their welfare or health status. In this study, rainbow trout eyed eggs were hatched and larvae were fractionated according to their emergence time (early fraction: first 20% of fish to emerge; intermediate fraction: mid 20%; late fraction: last 20%). When the fish were 4 months old, they were exposed to a daily repeated stress protocol for 15 days. The next day, both naïve and repeatedly stressed fish were exposed to an acute stress challenge. Different plasma (cortisol, glucose, lactate) as well as CNS (serotonergic activity) stress markers were assessed to evaluate the stress resilience of the different groups. Furthermore, an intraperitoneal infection challenge with was carried out to assess disease resilience. Altogether, the results showed that fish from different fractions displayed differences in activation of the hypothalamus-pituitary-inter-renal axis, indicating a higher stress resilience in the fish with early emergence times. However, those differences were not reflected in the ability of the different fractions to grow and perform well in terms of growth, or in the ability to overcome infection with bacteria, which was similar for all the emergence fractions. This suggests that discriminating fish according to emergence time would probably have little effect in improving the performance and the welfare of farmed fish.

Early performance, stress- and disease-sensitivity in rainbow trout fry (Oncorhynchus mykiss) after total dietary replacement of fish oil with rapeseed oil. Effects of EPA and DHA supplementation

“…The only observed effect of the repeated stress protocol on the fish acute stress response was a smaller peak in the plasma levels of lactate, and this effect was independent of the diet. The same result was observed before in another study using a similar protocol (Gesto et al, 2018). The reduction in the lactate response to the stressor suggests a faster lactate clearance rate or a reduced behavioral response to the stressor, resulting in less strenuous exercise and in a lower oxygen debt (Milligan and Girard, 1993).…”

“…shown to be highly diverse in their ability to habituate to repeated stress depending on their emergence time (Gesto et al, 2018). That large diversity might explain the lack of differences in the current study, where fish were not selected by emergence time.…”

“…Two challenge methods, an IP challenge and a bath challenge, were set up. The IP challenge, described by Madsen and Dalsgaard (1999) and used as challenge method in Gesto et al (2018), was chosen to investigate J o u r n a l P r e -p r o o f the disease resilience to infection with F. psychrophilum in fry that had been fed the different diets from first feeding, as this method has been shown to be a reproducible infection method resulting in high mortalities when it comes to F. psychrophilum. Besides the IP challenge, a F. psychrophilum bath challenge with stressors was also set up and performed as described below.…”

Consistent individual competitive ability in rainbow trout as a proxy for coping style and its lack of correlation with cortisol responsiveness upon acute stress

“…Even when a genetic link might exist between behavior and the physiological stress responses, it has been suggested that the plastic nature of vertebrate behavior and the different subjective environmental conditions can easily uncouple both aspects of coping styles [52]. In the same direction, it has been also suggested that the decoupling between HPI responsiveness and behavioral and life history traits usually associated to stress coping styles might be favored by the process of domestication [20,53,56].…”

“…In the current study, we wanted to get some information to investigate the stress response of the fish at the level of the CNS. The serotonergic system is believed to be involved in the organization of the integrated stress response in vertebrates [51,[57][58][59], and the activity of serotonergic neurons has been show to increase consistently upon stress exposure in fish [51,56]. The ratio between 5-HIAA and serotonin is used as an indirect estimator of the serotonergic activity, since 5-HIAA is usually produced after degradation of part of the 5-HT released at the synaptic terminal [59,60].…”