| Summary: | 1) Closed recirculating intensive aquaculture potentially offers major advantages over existing technologies including reduction in normal production time, reduced water input and output and beneficial environmental effects. 2) The major aim of this study was to produce a basic scientific understanding of the factors that affect intensive recirculating culture of the European eel Anguilla anguilla in order to increase efficiency and economic viability of eel aquaculture in the E.U. 3) Unlike some intensively farmed fish such as salmonids little is known of the stress factors affecting optimal growth rates in intensive eel culture. The primary effects of stress are mediated by corticosteroids and catecholamines which may have profound effects on growth, appetite and ion and water balance. 4) Growth rates of the eel Anguilla anguilla were investigated in closed water recirculating systems utilising fresh water or saline water (12 ppt)at 23°C. Eels were initially graded into two similar populations consisting of three categories, small (12g), medium (24g) and large (48g) based on initial growth rates. 5) During a 300 day period the medium and large group's growth rates were significantly greater in 12 ppt saline water than in fresh water, although for the small fish group there was no such difference. Stocking densities were maintained at commercial levels of approximately 30-100 kg/m3. 6) Plasma cortisol concentrations increased throughout the growth period in both fresh and saline water, although there were no significant differences between the two groups during the experiment. Metabolic clearance rates of cortisol were however consistently higher in saline water fish. 7) Both groups showed an increase in plasma glucose concentration throughout the experiment. However there were no significant differences between fresh water and saline water fish for plasma concentrations of glucose, free fatty acids or lactate. 8) Eels held at stocking densities of 130 kg/m3 continued to grow in the saline water whereas the ...
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