Impact of gillnet soaking time on survival, stress physiology, and muscle quality in Atlantic Cod (<i>Gadus morhua</i>)

The aim of this study was to investigate the effects of gillnet soak time to gain a better understanding of fish welfare, mortality, stress, and quality (as measured as muscle haemoglobin) during experimental gillnet fishery of Atlantic cod (<i>Gadus morhua</i>). An experimental study was conducted in a large-scale tank at a research facility with 131 wild-caught fish in four groups with gillnet soak times of 0, 2, 12, and 24 h (23-34 fish per soak time). Longer soak time caused higher mortality, with a mortality rate of 0, 7, 18, and 25% in the 0-, 2-, 12- and 24-h groups, respectively. Blood lactate levels were significantly affected by soak time, peaking at 2 h (with the widest confidence interval) and showing their lowest concentrations at 0 and 24 h. Soak time also significantly increased blood glucose and serum cortisol levels. Magnesium, creatinine, and iron increased significantly in all groups compared with control levels, but there was no significant difference between soak times. Haemoglobin content in the loin increased significantly only after 24 h of soak time for live fish. There was no significant increase in haemoglobin in the belly as a function of soak time. However, for all soak times, the belly had significantly more haemoglobin than the loin. Physiological evidence of traumatic injuries and stress were noted prior to increased muscle haemoglobin, meaning that good quality did not necessarily equate to good welfare. However, a higher level of muscle haemoglobin is a strong indication of poor welfare.