Study on the Effect of Weight & Salinity on Changes in Number and Size of Kidney Malpighian Bodies of Juvenile Caspian Sea Brown Trout, Salmo trutta caspius

In this research, based on an experiment, the number and size of malpighian bodies in juveniles of Caspian Sea brown trout (Salmo trutta caspius Kessler-1877) with different weights placed in solutions with various salinity were studied. For this purpose, juveniles with weights 2, 5, 10, 15 and 20 g were directly transferred to saline solutions with concentrations 0, 4, 8 and 12.5 g/L and were kept there for a period of 120 hours. By observing the results of histological changes, it was shown that the number and size of kidney malpighian bodies increase when the weight is increased. Also the number and size of kidney malpighian bodies are decreased when salinity increases. The results of mortality percentage until 120 hour shows that the juveniles of 2 up to 20 gr have no mortality in water salinities ranges of 0 up to 12.5 gr/lit which is a cue to the fact that they have a remarkable adaptability to the environmental condition changes. Considering the subtarget of this study that is determination of the proper weight and salinity for releasing juveniles Caspian sea brown trout as well as the obtained results of the experiment, it seems that juveniles of 2 up to 20 gr could be directly released in salinities of 0 up to 12.5 gr/lit and it is predictable to survive at such condition. But due to the fact that releasing the juveniles with higher weights in salinities near to seawater salinity by having an eye on the reduction of staying time in freshwater and also the reduction of the distance between releasing area and the sea could be helpful for the success of releasing process, it is recommended to release juveniles caspian sea brown trout of 10 gr which showed the proper histological changes among other weights as well as no mortality in salinities of 8 up to 12.5 gr/lit (same as estuary to seawater salinity) to achieve the proper releasing process.