Effects of perimortem stress on farmed Atlantic cod product quality: a baseline study

The potential effects of handling stress on the product quality of farmed Atlantic cod were studied in a controlled experiment (fish anesthetized with metomidate or isoeugenol, or subjected to stress by chasing for 30 min). For comparison, stress and fillet quality was also studied for commercially slaughtered farmed cod (fish sampled from waiting cage, after pumping and stunning with carbon dioxide, and after bleeding and chilling). Baseline values for stress-related parameters (blood chemistry, muscle high-energy phosphates and inosine monophospate, initial pH, muscle twitches, and rigor mortis) of rested Atlantic cod have been established. Since our stress bout showed that this species was not easily excitable, we were less convinced that we actually did study the other extreme, namely, exhausted fish. Nevertheless, the present data from the commercial slaughter of cod suggested that our stress bout was of adequate magnitude to represent potential poor handling routines. Our results consistently showed largely no differences between treatments, and that perimortem handling stress did not cause inferior flesh quality. This suggested that farmed cod can be processed with little risk of reducing product quality (quality index, fillet water content, water-holding capacity, ultimate pH, adenosine triphosphate-related degradation products and K-value, skin and fillet color, water and salt-soluble proteins, hardness, and gaping). For better maintenance of skin appearance after storage, the importance of storing the gutted cod on the belly, avoiding direct contact between skin and crushed ice, is demonstrated.