There is vast difference between saltwater fish and freshwater fish. This difference can easily be studied when you start and maintain a freshwater fish as well as saltwater fish aquariums. Generally people tend to start a freshwater fish aquarium and when they gain experience of maintaining aquarium they go for saltwater fish. In this topic we have discussed the difference between freshwater fish and saltwater fish. 

• Freshwater fish are more accustomed to variations in water conditions while saltwater fish are not accustomed to these variations. The reason for that is a freshwater fish life in water which gets affected whenever there is flood or drought, while sea water is not affected by floods or droughts. Therefore you have to take special care of saltwater fish when you put it in an aquarium.
  
  
• Another major difference between these two fishes is the quality of water in which they live. Saltwater fish lives in salty water and has less salt in its body than in water whereas freshwater fish has more salt in its body than the water in which it lives. Due to the process of osmosis saltwater fish when put in a tank will require more water to drink to maintain its salt balance. Similarly, freshwater fish is not that affected when put in a tank and doesn’t require so much water to drink.  Thus you have to maintain a specific gravity of water when you put saltwater fish in an aquarium.
  
  
• The type of food which is preferred by both these fishes is also a major factor when comparing both of them. Preferred food varies from species to species but saltwater fish is very particular about the food it eats..