The study was carried out by Delta Research Station, Canal Maintenance Research Institute, National Water Research Center. 300 grass carp (average body weight 20-30 g) were divided into three equal groups (100 fingerlings per group) in fiber glass basins of each 2000-liter basin, the first group was used as a control group (C), the second group was used 25 gm /m² of rice straw (B₁), the third group was used 50 g/m² of rice straw (B₂). The rice straw was used to control the growth of algae as a biological method. The study was conducted during the spring season for 10 weeks (mid-March to May 2011). This study examined some physiological and histological changes of the grass carp fish liver as a result of exposure to the compounds resulting from the decomposition of rice straw in water. Blood samples were withdrawn and transverse sections of the liver were performed two weeks after the beginning of the experiment.
            Results indicated that there were no significant effect of using 25 and 50 g/m² ricestraw on plasma total protein, liver glycogen and GST compared to the control group. Also, there were no significant differences between ALT recorded for the group 25 and 50 g/m² ricestraw of rice straw as compared with the control group throughout the study except after 3 or 5 weeks from the start of the experiment. On the other hand, glucose showed significant difference between 25 50 g /m² of rice straw throughout the study except weeks 2, 3 and 7.
The general histological examination indicated that there was no significant damage in tissues of grass carp liver after exposure to 25 or 50 g/m² of rice straw concentration for 8 weeks.
            It could be concluded from the previous results that rice straw (25 g/m²) application can be used in the biological resistance of algae in water courses as it does not have any effects on the bio-efficiency of fish and thus on the general health of humans.