Emergence Time and Skin Melanin Spot Patterns Do Not Correlate with Growth Performance, Social Competitive Ability or Stress Response in Farmed Rainbow Trout

Abstract

In wild salmonid fish, specific individual behavioral traits have been correlated with the timing of fry emergence from their gravel spawning nests; Early emerging fish display more aggressive behavior and have a higher probability of becoming socially dominant, compared to fish that emerge at a later stage. Apart from aggression and dominance, other behavioral and metabolic traits, such as boldness, metabolic rate, or growth, have also been linked to emergence time. Altogether, the traits of early- and late-emerging fish resemble those of the proactive and reactive stress-coping style, respectively. As proactive fish are considered more resilient to stress, it may be desirable to select these for aquaculture production. However, it is currently unclear to what extent the link between emergence time and stress-coping styles is maintained in the selective breeding of farmed fish. In the present study, eyed eggs from a commercial supplier were hatched, and larvae fractionated according to their emergence time. Later on, juvenile fish from different emergence fractions were subjected to a stress challenge and also tested to evaluate their competitive ability for food. Beyond some slight dissimilarities in the acute stress responses, emergence fraction displayed no correlation with growth rates, or the ability to compete for feed. Within the whole group of fish utilized in the experiments, no relationship between skin melanin spot pattern and growth performance, stress response intensity, or competitive ability was found. Altogether, the differences in physiological traits related to emergence time were not as strong as those found in earlier studies. It is hypothesized, that the origin and degree of domestication of the fish might be partly responsible for this. The predictive value of skin spots or emergence time to infer the fish stress coping style in farmed fish is also discussed.

Interplay between daily rhythmic serum-mediated bacterial killing activity and immune defence factors in rainbow trout (Oncorhynchus mykiss)

“…Screening strategy based on this stress-coping style is a promising approach in aquaculture, but there is a big lacuna in our understanding of the underlying mechanisms of these differences. The fish used in the present study was from a sister experiment that aimed to understand the physiological differences between the different emergence fractions in rainbow trout [17]. Since earlier evidence suggested that fish with proactive SCS was also more resistant to certain diseases [20,21], we speculated that there might be distinct immunological differences between the two fractions.…”

“…LED bulbs provided illumination and had a water surface intensity of around 320 lux. The hatching, fractionation and husbandry protocols are described in detail in Gesto et al [17].…”

“…Likewise, the daily oscillating patterns of selected humoral defence molecules were explored to provide insight into the underlying factors that may be contributing to the daily changes of serum bactericidal function. The variations in serum-mediated bacterial killing activity and immune defence factors were investigated in a comparative approach by employing rainbow trout originating from two different emergence time (often referred to the time for first feeding) fractions, namely the early-and the late-emerging individuals [17]. In the wild, the emergence time of salmonid is thought to be related to their stresscoping style (SCS): individuals emerging early are more proactive while those emerging late are thought to exhibit a reactive SCS [18,19].…”

Proactive coping style in early emerging rainbow trout carries a metabolic cost with no apparent return

“…Although we have shown that the rainbow trout in the present study show distinct behavioural and physiological phenotypes that correlate with emergence time, it is important to note that the genetic background of the fish is an important factor influencing the relationship between emergence time and the stress coping style. In a recent study, Gesto et al (2017) we showed that the emergence time did not correlate with the stress coping style in a population of rainbow trout that had been selectively bred for over 20 generations. It is possible that the selective pressure in breeding may diminish the phenotype diversity in terms of boldness/shyness, contributing to a higher behavioural homogeneity of the fish.…”

Confirmation that pulse and continuous peracetic acid administration does not disrupt the acute stress response in rainbow trout

“…The levels of serotonin (5-HT) and its main oxidative metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the telencephalon were analyzed using high performance liquid chromatography with electrochemical detection (HPLC-EC) as described by Gesto et al (2017).…”