The diagram describes the growth process of salmon, a kind of big fishes that live in 2 different water bodies throughout its life.
Overall, they are 3 process that they are going through, started with egg and ended up with adult salmon.
Salmon’s life are started in upper river while they are actually eggs. The eggs are located among the small stones and protected by reeds. These eggs need 5-6 months before they hatch. The hatched salmon that sized 3-8 cm are called fries. The fries are then move from the upper river to the lower river.
In the lower river where the stream flows faster than the upper river, the fries live their life for approximately 4 years until they reach the size of 12-15 cm. Once they come to this size, they are called smolts.
The smolts subsequently migrate to the open sea. For about 5 years they live here until they gain maturity. The mature salmon are called adult salmon that sized 70-76 cm. Finally, the adult salmon migrate once again to the upper river where they start the processes all over again. 
The diagram  
describes
 the growth process of salmon, a kind of  
big
 fishes that  
live
 in 2  
different
 water bodies throughout its life. 
Overall
, they are 3 process that they are going through,  
started
 with egg and ended up with adult salmon.
Salmon’s life are  
started
 in  
upper
  river
 while they are actually eggs. The eggs  
are located
 among the  
small
 stones and protected by reeds. These eggs need 5-6 months  
before
 they hatch. The hatched salmon that sized 3-8 cm  
are called
 fries. The fries are then  
move
 from the  
upper
  river
 to the lower river.
In the lower  
river
 where the stream flows faster than the  
upper
  river
, the fries  
live
 their life for approximately 4 years until they reach the size of 12-15 cm. Once they  
come
 to this size, they  
are called
  smolts
.
The  
smolts
  subsequently
 migrate to the open sea. For about 5 years they  
live
 here until they gain maturity. The mature salmon  
are called
 adult salmon that sized 70-76 cm.  
Finally
, the adult salmon migrate once again to the  
upper
  river
 where they  
start
 the processes all over again.