Modification of the Plasma Cortisol Response to Stress in Rainbow Trout by Selective Breeding

In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. Using 2nd and 3rd generation fish, we tested the hypothesis that differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. LR fish showed a tendency to become socially dominant, a rapid recovery of food intake after transfer to a novel environment, and a reduced locomotor response in a territorial intrusion test. Furthermore, stress induced elevation of brain stem and optic tectum concentrations of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress to a larger degree in HR than in LR trout. A divergent pattern was seen in the hypothalamus, where LR fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). Thus, selection for a single trait, cortisol responsiveness, in rainbow trout is associated with concurrent changes in both behavior and central signaling systems. The apparent parallel to genetically determined stress coping styles in mammals, and the existence of similar trait associations in unselected populations of rainbow trout, suggests an evolutionarily conserved correlation between multiple traits. Continuing studies on the HR and LR trout lines are aimed at providing the physiological and genetic basis for new marker-assisted selection strategies in the rapidly developing finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.

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Behavioral and Neuroendocrine Correlates of Selection for Stress Responsiveness in Rainbow Trout—a Review

Postmortem tenderization is caused by enzymatic degradation of key structural proteins in myofibrils as well as in extracellular matrix, and of proteins involved in intermyofibrillar linkages and linkages between myofibrils and the sarcolemma. The function of these proteins is to maintain the structural integrity of myofibrils. Current data indicate that calpains and cathepsins may be responsible for degradation of these proteins. Other phenomena occurring in cells postmortem (pH drop, sarcoplasmic Ca2+ increase, osmotic pressure rise, oxidative processes) may act in synergy with proteases. Our understanding of the underlying mechanisms of muscle degradation should be improved for an accurate evaluation of the postmortem muscle changes and consequently of the fish quality.

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Trends in postmortem aging in fish: understanding of proteolysis and disorganization of the myofibrillar structure.

. A reliable assessment of animal welfare-suffering and of its impact on product quality requires a multidisciplinary approach that takes into account fish behaviour and the different biochemical and physiological processes involved. This might be done by the contemporary study of changes of indicators of brain function, endocrine responses, post mortem tissue biochemical processes and quality changes. This work reviewed some of the most used indices of stress at the time of slaughter, commercial slaughter methods and related stress effects on physical and biochemical parameters of fish quality. The set of the available data seemed to indicate that, although of some results appear contradictory, pre-slaughter and slaughter stressful practices could have an important effect on the flesh quality in fish. A clear effect emerged mostly on the physical properties of flesh, because severe stress at slaughter time exhausted muscular energies, produced more lactic acid, reduced muscular pH, increased the rate of rigor mortis onset. In this way they could have significant negative effects on technological traits, flesh quality and keeping quality of fish. Asphyxia and electrically stunned fish were more stressed than spiked, knocked and live chilled fish. Combining various methods together might be a more satisfactory strategy for both animal welfare and product quality.

Fish welfare and quality as affected by pre-slaughter and slaughter management.

Recently, food safety and quality have become critical issues of great concern throughout the world. Fish is one of the most vulnerable and perishable aquatic products. The evaluation of fish and fillet freshness is therefore very significant in research and development for providing premium and supreme quality for human health and acceptance by consumers, as well as for international trade. The texture and structure of fish muscle are important freshness quality attributes that depend on several parameters such as hardness, cohesiveness, springiness, chewiness, resilience, and adhesiveness, as well as the internal cross-linking of connective tissue and the detachment of fibers. This review aims to present recent advances of texture and structure measurements and analyses, including sensory evaluation and instrumental methods, for indicating and evaluating fish freshness quality. Factors affecting these measurements are detailed and correlations between texture and structure are discussed. Moreover, the limitations and challenges of fish texture and structure measurements are described and some viewpoints about current work and future trends are also presented.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12043

Texture and Structure Measurements and Analyses for Evaluation of Fish and Fillet Freshness Quality: A Review.

Salmon slaughtered by standard routines (control) or stressed by confinement for 10 min before stunning and then stored at 0.4 or 3.3°C for 9 days were compared. Handling stress led to lower muscle phosphocreatine (p<0.001), adenosine-5′-triphosphate (p<0.05) and shorter pre-rigor period. Storage temperature affected external quality index, white muscle pH and K-value (degradation products of ATP). Stress produced a softer fillet (p<0.001). A lower breaking strength (p<0.01) was found in fish stored at 0.4°C. Sensory tests distinguished the control/stress groups within the 0.4°C chilling regime and the 0.4°C/3.3°C chilling groups within the control regime. Stress caused a lower score for texture (p<0.05) both at 0.4 and 3.3°C and for odor at 3.3°C in a descriptive sensory test. No detectable effects of stress or storage temperature were found on flavor or color.

Handling Stress and Storage Temperature Affect Meat Quality of Farmed-raised Atlantic Salmon (Salmo Salar)

La fermete est un important facteur d'evaluation de la qualite du poisson. Les experiences indiquent que le refroidissement au-dessous de zero degre est cause d'une periode de pre rigor plus breve et d'une evolution de la rigidite plus rapide que dans les procedes de refroidissement utilises aujourd'hui. Le manque de temps pourrait etre un probleme, s'il faut emballer le poisson avant l'etablissement de la rigor. L'objectif de l'etude est de demontrer les effets du refroidissement a basse temperature sur la fermete du poisson lors de l'etablissement de la rigor, et le risque d'effets negatifs a long terme sur la qualite. On a analyse les phosphates de haute energie, le pH, le glycogene, le glucose et le glucose-6-phosphate de haute energie des muscles blancs, avant et immediatement apres refroidissement dans la glace ou dans un reservoir d'eau de mer glacee. On a mesure l'evolution de la rigor mortis par methodes sensorielle et experimentale. On a determine la quantite de proteines solubles dans l'eau et dans le sel, le poids sec, la capacite de retention d'eau, apres trois et huit jours d'entreposage sur glace. La fraicheur du poisson est exprimee en valeur K. Les resultats ont montre une evolution plus rapide de la rigidite, une plus longue periode de rigor et une rigidite significativement plus grande du poisson pendant la rigor mortis, pour le poisson refroidi par cette methode. Il est apparu que la rigidite causee n'etait pas due a un debut precoce de rigor mortis, mais a un autre phenomene. Les parametres chimiques n'ont pas revele le choc du au froid . La temperature initiale d'entreposage a basse temperature ne semble pas avoir eu d'effets negatifs a long terme sur la fraicheur ou la qualite du poisson en general.

T. S. Nordtvedt

Papers

Handling Stress and Storage Temperature Affect Meat Quality of Farmed-raised Atlantic Salmon (Salmo Salar)

Effect of pre-packing temperatures on atlantic salmon quality. Discussion