Effects of dietary ascorbic acid/iron ratio on some production traits, lipid peroxide state and amount/activity of the glutathione redox system in African catfish Clarias gariepinus (Burchell) fingerlings

African catfish Clarias gariepinus (Burchell) fingerlings (3.16-3.92 g initial body weight) were investigated for 30 days in four different groups using different amounts of L-ascorbic acid (AA) and iron (supplied as FeC6H5O7) in their feedings. Diet 1 (control): no addition of AA or iron; diet 2 (H-AA/FE): high (600 mg kg-1) AA and low (218 mg kg-1) iron; diet 3 (H-HE/AA): high (364 mg kg-1) iron and low (200 mg kg-1) AA; and an unfed group, which was investigated only for 15 days due to high mortality. The live weight gain, feed intake, specific growth rate (SGR; % body weight day-1) and feed conversion rate (FCR) were measured or calculated. At the end of the experimental period, the whole body content of AA, iron, reduced glutathione (GSH), glutathione disulphide (GSSG) and malondialdehyde (MDA), as well as the glutathione peroxidase (GSHPx) activity, were measured. The production traits did not differ significantly as a result of the different AA and iron contents of the feed. AA content increased significantly in all the groups as compared with the initial value, except in the unfed group. The difference between the treated groups as compared with the control, with regard to the two AA/iron treated groups, was also significant. The iron content in the fish body increased significantly compared with the initial value, except in the unfed group. The difference compared with the control was significant only in the H-FE/AA group. The difference between the groups that consumed low and high iron content diets was also significant. The GSH and GSSG content, as well as the GSH/GSSG ratio and GSHPx activity of the fish body, did not differ significantly as compared with the initial value or with the control. The lipid peroxide status, as measured by the MDA content, did not differ significantly either as an effect of the AA and iron supplementation, but decreased as an effect of ageing and starvation. It may be concluded that, under the present experimental conditions, the C. gariepinus fingerling tissue stores of AA and/or iron increased as a result of feed supplementation, but without altering the actual lipid peroxide status and the amount/activity of the glutathione redox system.