The effects of daily fluctuating temperatures and dimethylnaphthalene contaminated food on the estuarine grass shrimp, palaemonetes pugio

The physiological effects of a natural perturbation (fluctuating. temperatures) and a petroleum-induced perturbation. (dimethylnaphthalene-contaminated food) on the grass shrimp. Palaemonetes pugio were compared. The resistance of shrimp to. environmental challenge, oxygen consumption rates (Vo(,2)) and(\u27 ). several physiological indices of stress were determined after a 32. day exposure to fluctuating temperatures (FT) (18-22�C) and/or dimethylnaphthalene (DMN)-contaminated food (0.24 (mu)g DMN/g wet wt) and again after a 16 day recovery period of stable temperatures (20�C) and uncontaminated food. Both FT and DMN-contaminated food reduced survival to the challenge of hypoxia + reduced salinity. FT were quantitatively more stressful than either stable temperatures or DMN-contaminated food. After the recovery period, FT did not affect survival to hypoxia, while shrimp, which had ingested DMN-contaminated food, exhibited enhanced survival to hypoxia. Ingestion of DMN-contaminated food for 32 days resulted in elevated Vo(,2)(\u27 )in shrimp exposed to declining oxygen concentrations. After the 32 day exposure period, FT had no significant effect on(\u27 )Vo(,2) at 15�C, 20�C and 25�C, tissue Vo(,2),(\u27 )Vo(,2) in declining oxygen and hemolymph copper concentrations. After the 16 day recovery period, shrimp from the FT regime exhibited depressed(\u27 )Vo(,2) when exposed to 25�C but not to 15�C. These depressed respiratory rates were offset by the stimulatory effect of DMN-contaminated food. The ratio of oxygen consumed to nitrogen excreted wwas elevated after the exposure and recovery periods in shrimp exposed to both FT and DMN-contaminated food at the same time. Water flux rates were elevated by FT after the exposure and recovery periods but not when DMN-contaminated food was also ingested. Both water flux rates and the ratio of oxygen consumed to nitrogen excreted were elevated in all shrimp after the recovery period relative to levels observed after the exposure period. After the exposure period, FT induced elevated hemolymph acid phosphatase activities in shrimp exposed to hypoxia. After the recovery period, hypoxia induced elevated hemolymph acid phosphatase activities in shrimp which had ingested nothing but uncontaminated food relative to those ingesting DMN-contaminated food