The effects of petroleum exposure on the feeding behaviour of rainbow trout (Oncorhychus mykiss) using the water-soluble fraction of Norman Wells crude oil

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Ryan, Michael J.
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The effects of exposure to the water-soluble fraction (WSF) of Norman Wells crude oil (NWC) on the feeding behaviour of rainbow trout were studied. Trout were exposed to WSF of NWC mixed at 10, 25, 50, 100, 200 and 400 mg/L nominal concentrations. Exposures lasted 14 days with complete, daily renewal of the WSF in a static, non-aerated system. Nominal hydrocarbon (HC) concentrations were compared with measured concentrations by extracting water with hexane and analyzing the samples with mass spectroscopy gas chromatography. At 400 mg/L nominal (8.27 mg/L measured) HC concentrations, all the fish died within 96 hours. Between 50 mg/L and 200 mg/L nominal concentrations (0.55-1.92 mg/L measured concentrations), feeding became noticeably slower within 2 days and stopped completely by 3 days. The fish displayed signs of narcosis and swimming impairment with $>$92% decrease in food consumption. The 'lowest observable effect' concentration (LOEC) was 25 mg/L nominal (0.31 mg/L measured). Feeding slowed after 5 days resulting in a decrease in food consumption $>$54% after 14 days when compared to controls. No effects on feeding behaviour or body water content were evident at the 'no observable effect' concentration (NOEC) of 10 mg/L nominal (0.14 mg/L measured) HC concentrations. The maximum allowable toxicant concentration (MATC) for the alteration of feeding behaviour in young rainbow trout ranged between NOEC and LOEC at 0.14 to 0.31 mg measured HC per litre of water. No significant trend was seen in the wet weight and lengths of the fish during the experiment probably because of the short exposure duration (14 days). There was a small increase in body water content in the exposed fish relative to unexposed controls.