Experiments were carried out to identify the environmental factors influencing survival during emersion with the aim of suggesting modifications to present transit conditions in order to minimise physiological stress, thus improving scallop condition and survival. Results showed that increasing the emersion temperature from 5 to 20oC caused a reduction in maximum survival time of 62%. Similarly, reduction in relative humidity, from 95 to 70% saturation, resulted in 27% reduction in maximum survival time. Scallops exposed to a fine sea-water mist showed a 13% improvement in survival and the survival of scallops tested in December was 67% better than those tested in July. This seasonal effect appeared to be correlated with tissue glycogen concentrations which decreased by 29% over the same period. Maximum survival of any emersed scallop was 166 hours, although the animals were not in an edible condition after this time. Experimental factors which were found not to influence survival directly were packing orientation, enforced shell-valve closure and hypertoxic conditions (˜100% oxygen). These results implicated aspects of energy metabolism as the primary causes of scallop death during emersion and therefore this area was investigated in more detail. Further work showed that, heart rate had a positive linear relationship with temperature until ˜19oC. Thereafter, heart rate became irregular and uncoordinated, suggesting that poorer survival at high temperature is caused by loss of physiological integration and difficulty in meeting increased metabolic demands. The oxygen consumption rate of Pecten maximus in air is reduced to only 50% of the aquatic rate within 8 hours of emersion. This decline in respiration rate continued and was typically between 25 and 30% of the aquatic oxygen consumption rate after 60 hours in air. In addition, heart rate, haemolymph PO2, haemolymph pH and mantle cavity fluid PO2 and pH all decreased during emersion, implying that respiratory and circulatory systems were deteriorating.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:513317 |
| Date | January 1993 |
| Creators | Duncan, Peter Fergus |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/1911/ |
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