The stunning and killing efficiency of ice, superchilling (N₂gas), freezing (-37°C), gradual heating (40°C), boiling, piercing of ganglia, salt baths (NaCl and KCl), gas (CO₂) and electricity (50 Hz AC) on edible crabs was studied. Results showed that electricity was the most efficient stunning method, whereby edible crabs could be rendered insensible within 1 s using electric field strengths of 400 V m⁻¹and above. Prolonging the electrical current to 10 s resulted in less potential difference (220 V m⁻¹) required to stun the crabs. Applying a two-stage stun with 530 Vm⁻¹for 1 s followed by 170 V m⁻¹for 2 min resulted in a state of prolonged unconsciousness and 60% mortality. Failure to stun the crabs with electricity resulted in massive autotomy, where all appendages were lost. Behavioural responses were lost in approximately 30% of crabs after 100 min of chilling on ice, while freezing did not render the crabs unconscious until temperatures of subzero were reached. The exposed chelipeds stiffened, and once frozen, irreversible damage was caused. Placing crabs into heated seawater (40°C) led all responses to be lost after 5 min, while the internal temperature exceeded an average of 26°C, representing approximately 2.5 min of boiling. Gas, in the form of CO₂, NaCl, and a low concentration of KCl (5%), failed to render the animals insensible within 12 min. Using 20% KCl saw all animals lose all behavioural responses within 3 min. The piercing of single ganglions failed to kill the animal; both ganglia must be pierced in order to kill the animal. We conclude that electrical stunning is recommended prior to boiling or carving, while piercing can alternatively be carried out by trained personnel.

During the commercial slaughter of farmed turbot(Scophthalmus maximus), a total of 67 fish were, on six occasions, removed from their rearing conditions at 14°C and put, as is standard commercial practice, into chilled seawater (-1.5 to -0.8°C) to monitor behavioural, muscular, osmoregulatory and respiratory responses during chilling time (90 min). Results show that a thermal insult alters the iso-osmotic balance, leading not only to an Na⁺influx and an intracellular release of Ca²⁺and K⁺, but also to a disturbance of respiratory function, leading to acidosis as a result of H+ and CO₂accumulation, increased pCO₂and reduced HCO₃⁻in the blood. Once the internal temperature dropped below 1°C, the muscles contracted (cold shortening) and, although the fish were still alive, they reverted to a state of rigor, leading to a complete breakdown in their ability to move or ventilate and resembling an unconscious condition or death. Remarkably, the fish were able to prevent themselves undergoing hypoxia as pO₂remained within acceptable limits. No changes in muscle pH were observed and, thus, no noted effects on textural properties. We conclude that live chilling from 14°C to approximately -1°C is a highly questionable practice. It causes physical and physiological changes that are generally associated with stress and, in the case of observed forced muscle contractions, could lead to severe pain. Furthermore, we conclude that cold shortening associated with chilling can be easily mistaken forrigor mortisand, as such, should be subject to further attention in future research on quality.

Several major market operators argue that the current level of knowledge about quality is too scant to justify a switch to a large-scale production of triploid salmon. The aim of the present study was, therefore, to elucidate how rearing conditions (5, 10 and 15°C) affect the flesh quality of triploid Atlantic salmon (Salmo salar L., 1.6±0.3kg). As a reference, diploid salmon kept under equal conditions and with equal genetics were used. The main design discriminant was the holding temperature; increased temperature gave increased blood lactate, rigor index (Ir), drip loss (DL), content of astaxanthin and intensity of redness, but reduced muscle pH, cathepsin activity and fillet lightness. Salmon kept at 10°C grew the fastest. It is concluded that ploidy gave less variation than temperature. Triploids were characterized by lower blood haematocrit (Hct) and Ir, higher DL and collagenase activity, and on average, paler and less yellowish fillets.

Crowded (stressed) and unstressed Atlantic mackerel with or without pre-freezing holding in refrigerated sea water (RSW) were stored at -19 °C for ∼12 months and analysed for nucleotide degradation (K value), muscle pH, water holding capacity (WHC), fillet firmness, cathepsin B/L like activity, lipid oxidation and fillet colour. The frozen storage showed the largest and most consistent direct effects on the quality metrics leading to increased lipid oxidation, discolouration (yellowing) and reduction on WHC and cathepsin activity. RSW treatment promoted nucleotide degradation and reduced WHC and fillet firmness in interaction with frozen storage and affected fillet colour lightness and saturation. Although showing only marginal main effects, crowding stress modified WHC, cathepsin activity and fillet firmness and colour through significant interactions with the frozen storage and RSW treatment. Further studies with larger sample sizes would be needed to elucidate their complex effects and interactions on the quality and storage stability of mackerel.