Impact of phenolic compounds on free amino acid contents and electrophoretic patterns of the Nile Tilapia, Oreochromis niloticus

The present research was designed to determine the free amino acids (FAAs) composition and electrophoretic protein patterns by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in  Oreochromis niloticus exposed to 1/10 LC₅₀-96 hrs of phenol and nonylphenol ethoxylate 9 (NPEO 9) under laboratory condition for 4 weeks, in an attempt to develop sensitive bio-indicators for evaluation of pollution effects. Variations of FAAs were apparent in both treated groups. Significant increases were recorded in all individual amino acids including essential and non-essential ones, except for proline for both treated groups and leucine for phenol exposed fish group where they decreased significantly. The electrophoretic analysis of protein of the skeletal muscle homogenate using SDS-PAGE indicated that the control group yielded 10 fractions of molecular masses between 166 and 23 kDa. A total number of 9 bands were separated from fish of phenol group; they were varied from 168 to 23 kDa. However, 6 bands only were separated from fish of the NPEO 9 group; they were varied from 157 to 28 kDa. The muscle protein extract from fish of the phenol group showed five unique bands (168, 96, 68, 52, and 39 kDa). Moreover, fish that were exposed to NPEO 9 group showed three unique bands (157, 92, and 72 kDa). The highest similarity index "S" value observed between phenol and control groups was 0.37, followed by 0.33 between NPEO 9 group and the control one. This could be an indicator of changes in protein metabolism due to phenol and NPEO 9 pollution.