Answer:
Maybe it is 5.50 because not much information is given to calculate it or to find it.
Oxygen, neccessary for cellular respiration, is the answer. As oxygen becomes scarce, your cells begin to aerobically produce very little ATP, in effect fermenting and producing lactic acid.
When the fish is put into fresh water, suddenly the concentration around them is very low and the water potential is extremely high. Water will now move from the relatively high water potential in the water to the relatively low water potential in the cells, the cells start to burst and the fish dies.
Development of breast tissue
