The effect of parasitism of European eels with the nematode, Anguillicola crassus on the impact of netting and aerial exposure

Introduction of the blood feeding swimbladder parasite, Anguillicola crassus, into Europe in the 1980s led to its establishment in the European eel, Anguilla anguilla, and more recently the parasite has been identified in the American eel, Anguilla rostrata. Mass mortalities of wild European eels infected with A. crassus suggested that infected eels may be more stressed by extreme changes in environmental conditions than uninfected eels, but the effects of aquacultural stressors are unknown. The present study therefore compared the physiological effects of netting and aerial exposure on European eels infected with A. crassus and uninfected eels. Both A. crassus-infected and uninfected eels showed a significant endocrine response to the 4 h of netting confinement and aerial exposure. Cortisol responses of parasitised and non-parasitised eels were similar with recovery by 4 h despite continued exposure to the stressors. Although there were no significant differences between the plasma glucose concentrations of eels infected with A. crassus and uninfected eels, at any of the blood sampling points in the netting and aerial exposure, differences in the dynamics of glucose mobilisation and utilisation are suggested. Plasma glucose concentrations rose significantly in infected eels, peaking at 135.0ł19.8 mg/100 ml after 2 h compared to basal levels of 59.46±11.2 mg/100 ml. This, together with a positive correlation between plasma glucose and total worm load at time 0 h, leads us to hypothesise that glucose mobilisation and utilisation is increased in Anguillicola-infected eels as a result of the metabolic strain of harbouring a blood-feeding parasite, and that aquacultural stressors further elevate glucose turnover. As glucose is an important metabolic fuel in eels, the growth and subsequent yield of farmed eels infected with A. crassus may potentially be compromised.