| Summary: | Improved animal welfare during industrial slaughtering of fish is the aim of the scientific work presented in this thesis. The thesis is based on four publications that cover different stages of an automated industrial slaughtering line for fish. The publications are presented in a similar order to those on a slaughtering line. The results from paper I are relevant for all types of pre-chilling of fish before slaughtering and reveal the physiological effects of live chilling in Atlantic salmon (Salmo salar). Chilling of fish is commonly used in the industry, both during transportation and processing of the fish in the slaughtering house. The publication is based on two experiments where the first experiment included fish (mean weight 840 g) acclimatized to a water temperature of either 16, 8, or 4°C and which were directly transferred horizontally or vertically (9 combinations) to temperatures of 16, 8, 4, or 0°C using a dip net. In the second experiment, fish (mean weight 916 g) acclimatized to 16°C were exposed to four temperature-drop regimes (no physical handling): 16–4°C (over 5 h), 16–4°C (over 1 h), 16–0°C (over 5 h), and 16–0°C (over 1 h). Physical transfers in the first trial, i.e., temperature drops, resulted in immediate (1 h) increases in blood lactate concentrations at all three temperatures, but levels were significantly reduced and close to pretransfer levels after 6 h. Horizontal transfers, i.e. 16–16°C, 8–8°C, and 4–4°C, resulted in similar increases and were not significantly different from the groups exposed to temperature drops. The most severe vertical transfer (16-0°C) resulted in a swift loss of equilibrium and eventually death. In experiment No.2, temperature drops from 16 to 4°C and from 16 to 0°C over a period of one or 5 h, without physically handling the fish, resulted in no significant increases in any of the measured parameters 1 h post-transfer, except in the 16–0°C (1 h) group. The latter experienced a significant increase in blood sodium, glucose, lactate and cortisol levels ...
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