Research Article: Imbalance of the redox system and quality of tilapia fillets subjected to pre-slaughter stress

Date Published: January 15, 2019

Publisher: Public Library of Science

Author(s): Elenice Souza dos Reis Goes, Marcio Douglas Goes, Pedro Luiz de Castro, Jorge Antônio Ferreira de Lara, Ana Carolina Pelaes Vital, Ricardo Pereira Ribeiro, Juan J. Loor.


The objective of this study was to evaluate the effect of oxidative stress on the instrumental and sensory quality of Nile tilapia fillets. The experiment was conducted in a 2×2 factorial arrangement, evaluating densities (60 and 300 kg m-3) and depuration times (1 and 24 hours) in a total of four treatments. The serum levels of cortisol and gene expression levels of catalase (CAT), glutathione peroxidase (GPx) and 70 kDa heat shock protein (HSP70) as well as the pH, color, tenderness, water-holding capacity and sensory analysis of the fillets were evaluated. High density (300 kg m-3) resulted in higher mean cortisol levels, lower expression of CAT and GPx enzymes as well as higher expression of HSP70. Fish under this treatment also exhibited fillets with greater tenderness, higher lightness, lower redness and lower sensory acceptance. The longer depuration time (24 hours) resulted in lower expression of the CAT and GPx enzymes and fillets with higher lightness. The water-holding capacity was not affected by the different treatments. Therefore, low density and longer depuration times are recommended for decreased stress and improved quality of fillets.

Partial Text

Stress is a condition of high aerobic energy demand to supply the body’s maintenance mechanisms during activation for adaptation and resistance of the body to stressful conditions [1]. In aquaculture, fish are subjected both to acute stressors, such as handling, and chronic stressors, including environmental changes (such as temperature, water quality and salinity), interactions with other fish and prolonged physical stress (such as transport and increased densities) [2].

Method was carried out in accordance with the guidelines of the Brazilian College for Animal Experimentation (COBEA; and was approved by the Committee on Animal Care of the Universidade Estadual de Maringá—Brazil.

In fish, acute stress exposure causes rapid elevation of cortisol levels, which are quickly restored to resting levels during recovery from stress [21]. In the present study, the increase in the density of tilapia for a short period of time increased serum cortisol levels regardless of the density being high or low. However, the maintenance of fish at low density allowed recovery from stress over time, which did not occur at high density. In general, plasma cortisol levels increase rapidly after exposure to acute stress, and normal conditions are restored within a few hours [22].

High density (300 kg m-3) during tilapia pre-slaughter causes lower expression of the CAT and GPx enzymes but higher expression of HSP70, resulting in the production of fillets with higher tenderness, higher lightness, lower redness and decreased sensory acceptability. Low density and longer depuration time are recommended for decreased stress and improved quality of tilapia fillets.




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