Metabolic trade-off between locomotion and detoxification for maintenance of blood chemistry and growth parameters by rainbow trout (Oncorhynchus mykiss) during chronic dietary exposure to copper

The aim of this study was to obtain a holistic view of the sublethal toxic responses, and compensations, of fish exposed to Cu in the diet. Rainbow tr out were fed to appetite on either a Cu-loaded diet (500 mg Cu kg(-1) dw) o r a control diet (11.9 mg Cu kg(-1) dw) for 3 months. Nutritional performan ce, blood and muscle chemistry, histology, respiration, and swimming behavi our were measured. Copper concentration in intestine and liver of exposed f ish was 16 and 2.5 times greater than in controls respectively, confirming oral Cu exposure. [Cu] remained low in the gills of fish irrespective of Cu treatment (< 0.096 mu mol g(-1) dw). Hepatic and intestinal metallothionie n levels increased 8-and 1.5-fold, respectively, in Cu-treated fish compare d to controls. Growth rate, appetite, food conversion ratios, carcass compo sition, oxygen consumption and ventilation rate in exposed fish were not di fferent from controls. There were no treatment related changes in serum che mistry (glucose, triglycerides, protein, Na, K, Hb) or the mineral composit ion of skeletal muscle (Ca, Mg, Zn, Na, or K). However, quantitative histol ogy showed a 9% increase in gill secondary lamellae length, together with l ipid depletion in the livers of copper treated fish compared to controls. R outine swimming activity was affected significantly by oral Cu exposure. Ti me spent swimming was 35% lower in Cu-exposed fish after 3 months, while to tal distance moved was reduced by only 21% because mean swimming speed was 12% higher in contaminated fish. Maximum speeds attained by exposed fish we re not different compared to controls. Exposed fish lowered activity overal l by decreasing time spent swimming at low (1-17 cm s(-1)) and medium speed s (17-40 cm s(-1)), whilst increasing proportionately time spent fast swimm ing (40-58 cm s(-1)). These results are discussed in terms of sub-lethal or al Cu affecting the partitioning of energy utilisation between locomotion a nd maintenance metabolism by trout in a physiological drive towards invaria nt growth rates. (C) 1999 Elsevier Science B.V. All rights reserved.