Dietary copper exposure in the African walking catfish, Clarias gariepinus: Transient osmoregulatory disturbances and oxidative stress

There are few dietary Copper (Cu) toxicity studies on warm water fish. We used the African walking catfish (Clarias gariepinus) to perform the first in vivo dietary Cu toxicity study on this species. We measured end points normally associated with metal toxicity (nutritional performance, haematology, histology, tissue Cu, Na+, and K+, Na+K+-ATPase activity) and add to the limited data on oxidative stress during dietary Cu exposure (thiobarbituric acid reactive substances or TBARS, and total glutathione). Clarias gariepinus were fed to satiation on a Cu-loaded diet (1500 mg Cu kg−1 dw feed), or a control diet (15 mg Cu kg−1 dw feed), for 30 days. Dietary copper exposure caused elevated Cu concentrations in the intestine (20 fold), liver (5 fold) and gills (4 fold) of Cu-exposed fish compared to controls after 30 days (ANOVA, P < 0.05). Copper-exposed fish showed a reduction in food intake and specific growth rate (SGR), but only very modest reductions in mean body mass at the end of the experiment (the latter not statistically significant). There were no treatment-dependent effects on food conversion ratio or proximate composition, and only transient disturbances to tissue electrolytes and Na+K+-ATPase activity. Haematology was normal throughout the experiment. Cu-exposed fish showed an increase in TBARS in the gill (1.5 fold) and intestine (2 fold increase) compared to the controls (ANOVA or Kruskal–Wallis, P < 0.05). Total glutathione content in the intestine of Cu-exposed fish doubled by the end of the experiment compared to controls, reaching 12.7 ± 2.85 μmol g−1 wet weight (mean ± S.E.M., n = 6, Student's t-test, P < 0.05). The liver showed some glycogen depletion consistent with reduced food intake, but no overt pathologies in the gills, liver or intestine were observed.