The general rule is 1 inch per gallon but this is more of a very rough guideline than a rule for reasons such as tuxyu3 has stated above^^
For example, a 10 gallon tank will hold 10 1 inch fish such as neon tetras but it won't hold 1 10 inch fish like a jack Dempsey. So it's almost an impossible to give a set answer to your question without know things like what kind of fish you are interested in keeping.
Another thing to take into account is tank dimensions. Even though your tank is 190 litres it won't be as suitable for some fish as say a Rio 180 would be, even though yours is 10 litres more than the Rio. This is because a Rio 180 has a larger footprint than your tank, meaning the bottom area is larger giving more swimming space.
And as tuxyu3 also said, it depends on what filtration you have and how much water % your changing per week. External filters are always better than internals and the more filtration the better really. You are ideally aiming for around 4-5x your tank volume so in your case you will need around 1000 litres turnover per hour.
Most people tend to change anything from 30-50% of water per week but again it depends on filtration and tank stock.