Effects of emersion and re-immersion on physiological and immunological variables in creel-caught and trawled Norway lobster Nephrops norvegicus.

Immune defence in creel-caught and trawled Nephrops norvegicus was investigated to assess a possible relationship between phenoloxidase (PO) activation and the total haemocyte count (THC). Capture, capture method and emersion evoked physiological and immunological responses that may have implications for the ability of N. norvegicus to survive the effects of such stressors. Haemolymph THC was always negatively related to PO activity in the trawled samples, suggesting a decreased level of the plasma serine proteinase inhibitors which reportedly regulate the ProPO system (Le Moullac et al. 1998; Fish shellfish Immunol 8:621-629). In contrast, creel-caught samples showed increased levels of both PO and THC (cf. control N. norvegicus), after a 12 h emersion period. Trawling and emersion evoked progressive and significant increases (p < 0.05) in the mean levels of haemolymph L-lactate, glucose and total ammonia. The evidence of overt activity and measured haemolymph parameters suggest that creel fishing yields N. norvegicus that are more likely to survive post-harvest treatments than those that are trawled.

Effects of emersion-induced hypoxia on some haemolymph constituents of Nephrops norvegicus.

The effects of prolonged emersion (24, 48 and 72 h) and subsequent re-immersion on Nephrops norvegicus (L.) held at 5 degrees C were assessed using an index of physical quality criteria and a suite of haemolymph constituent assays. Collectively, these showed classical hypoxia-induced changes over 48 h of emersion, but, subsequently, between 48 and 72 h emersion, physical activity, haemolymph pH and circulating levels of urate, free amino acids and major ions all returned to normal (control) levels, and L-lactate levels had started to decrease towards control levels. These patterns of changes differed from that of the haemolymph total ammonia levels which continued to increase linearly throughout emersion. N. norvegicus appeared to partially compensate for the post- 48 h emersion increased levels by increasing the production, and hence relative proportions, of other less toxic nitrogenous metabolites. The data replicated that of preliminary trials. Working on the presumption that such events could occur only in the presence of oxygen, possible sources of such oxygen under prolonged hypoxia are discussed. The low holding temperature appears to be the key to prolonged survival of N. norvegicus, and the switch from anaerobic to aerobic respiration itself appears to be a function of a preceding, prolonged period of hypoxia. The ecological and commercial implications for a burrow-dwelling, benthic animal that may experience episodic periods of hypoxia and which forms a highly important proportion of the value of total UK commercial landings are discussed.