Effects Of The Dietary Lead (Pb) On Energy Budgets Of Southern Catfish(Silurus Meridionalis Chen)

Three diets including different Pb levels of0(the control),2500and5000μg Pb/g were formulated. The southern catfish, Silurus meridionalis were fed with experimental diets at a meal size of2%body mass for eight weeks at27.5℃. The components of the energy budgets of equation and Pb accumulation in the various tissues of the fish were assessed, to investigate the rules of changes in components of the energy budgets of equation and Pb accumulation when fish exposed to dietary PbThe main results observed in this study were as follows:1. Neither the condition factors (CF) nor feeding rates (FR) of the fish were significantly affected by Pb treatments. However, the specific growth rates (SGRW) of the fish decreased with increasing dietary Pb levels. The SGRW of fish exposed to5000μg Pb/g treatment was significantly lower than that of other two treatments (P<0.05), whereas there was no significant difference between2500μg Pb/g group and the control. The feed efficiencies (FE) decreased with increasing dietary Pb levels. And the differences among the three treatments were significantly (P<0.05). The hepatosomatic indices (HSI) of the tested fish increased with increasing dietary Pb levels, and the HSI of5000μg Pb/g group was significantly higher than that of other groups (P<0.05). But no significant difference was detected between2500μg Pb/g group and the control.2. None of the parameters (contents of protein, lipid, ash, dry body mass and energy density) was significantly affected by Pb treatments. However, both the contents of protein and energy density decreased with increasing dietary Pb levels, an opposite trend was found in content of ash.3. There was no significant difference about normalized resting metabolic rates (mg O2/kg/h) among Pb treatments and the control. Normalized peak metabolic rates(Rpeak) of2500μg Pb/g group were significantly higher than that of5000u.g Pb/g group or the control (P<0.05), whereas the Rpeak of5000μg Pb/g group were significantly lower than that of the control (P<0.05); Factorial metabolic scope (FMS) in the two Pb treatment groups was not significantly different from the control, however, the FMS of2500μg Pb/g group was significantly higher than that of the5000μg Pb/g group (P<0.05); Although there was no significant difference for the peak times of SDA among the three groups, it increased with dietary Pb levels; The SDA duration increased with increasing dietary Pb levels. And that in Pb groups were significantly higher than that in the control (P<0.05); The SDA coefficient (%) increased with increasing dietary Pb levels, and the difference was significant between5000μg Pb/g group and the control (P<0.05).4. Neither the energy allocated on growth or resting metabolism was affected by Pb treatments, whereas the energy allocated to SDA, fish activity, lost in feces and excreta increased with increasing dietary Pb levels. The percentages of food energy available for growth in fish exposed to high dietary Pb levels was significantly lower than that of the lower Pb treatment or the control (P<0.05). And there was no significant difference between the2500μg Pb/g group and the control. Both the percentages of energy lost in feces and excreta in5000μg Pb/g group were significantly higher than that of the2500μg Pb/g group or the control (P<0.05), whereas there was no significantly difference between2500μg Pb/g group and the control. The percentages of food energy allocated to metabolism in the Pb treatment groups were significantly higher than that of the control (P<0.05).5. Pb accumulation in the various tissues of the fish increased with increasing dietary Pb levels, and the values in Pb treatment groups were significantly higher than that in the control (P<0.05). Except for the brain, the concentrtion of Pb accumulation in the other tissues for the5000μg Pb/g group were significantly higher than that for2500μg Pb/group (P<0.05). The concentration of Pb accumulation in the whole fish exposed to dietary2500and5000μg Pb/g were (0.51±0.04) and (0.73±0.02) μg Pb/g respectively, and the difference was significant among the three diets. The orders of Pb accumulation in the various tissues of the fish were different between the two Pb treatments. The order of Pb accumulated from sampled tissues for2500μg Pb/g diet was as follow:gill> liver> kidney> guts> carcass> stomach> brain> muscle, and concentrations of Pb accumulation in kidney, liver and gill were significantly higher than that of the other tissues; That for5000μg Pb/g diet was as follow:kidney> liver> gill> guts> carcass> stomach> brain> muscle, and concentrations of Pb accumulation in kidney, liver and gill were also significantly higher than the other tissues.The conclusions suggested in this study were as follows:1. The growth of southern catfish were inhibited when exposed to dietary Pb, this may resulted from lower feed efficiencies, longer SDA duration and higher energy expenditure during SDA under the stress of Pb exposure.2. The results suggested that long-term dietary Pb exposure could alter the patterns of energy allocation in the fish, which led to fish reallocate the digestible energy in food. The energy deposited as growth decreased when fish exposed to dietary Pb, while the percentages of energy for metabolism, lost in feces and excreta all increased.3. Dietary Pb could be accumulated in the southern catfish, however, a lower retention rates (0.27-0.41‰) were found in the fish body. It was also found that the Pb accumulation occurred in a dose-dependent manner in all measured tissues. Meanwhile, the ability to Pb accumulation in various tissues of fish were different:a relatively higher level Pb accumulation was in kidney, liver, gill or bone, and the lowest level Pb accumulation was in muscle regardless of the Pb exposure concentrations.