Effects of elevated dietary copper concentrations on growth, feed utilisation and nutritional status of Atlantic salmon (Salmo salar L.) fry

The present experiment was conducted to study effects of elevated dietary Cu and establish upper limits of Cu in fish feed. Atlantic salmon fry were reared for 3 months on experimental diets containing either 5 (control), 35, 500, 700, 900, or 1750 nag Cu kg(-1), provided as CuSO4 . 5H(2)O. Dietary Cr2O3 was included (1%) in all experimental diets for the last two weeks in order to assess apparent digestibility of both major food components and availability of minerals (Cu, Zn and Se). Growth was significantly (P < 0.01) reduced after 3 months at dietary Cu concentrations of greater than or equal to 500 mg Cu kg(-1) compared to the 35 mg Ca kg(-1) group. Similarly, whole-body content of protein, glycogen and Se were significantly reduced at these dietary Cu concentrations compared to controls. Apparent digestibility (%) of the major food components and availability of Zn and Se did not differ among dietary treatments. However, apparent availability of dietary Cu was significantly reduced in fish fed experimental diets containing less than or equal to 900 mg kg(-1) compared to controls. Whole-body minus intestine Cu concentrations were only significantly increased in fish fed dietary Cu concentrations greater than or equal to 900 mg Cu kg(-1) compared to controls, indicating a strong intestinal regulating capacity of dietary Cu uptake. Dietary Cu concentrations of 500 mg Cu kg(-1) and above caused toxic responses in Atlantic salmon fry as concluded from the antagonistic interaction with Se, and reduced growth and whole-body energy stores (protein and glycogen). (C) 1999 Elsevier Science B.V. All rights reserved.