i have just started a tank,160 litre,never done before,i noticed one fish over the past two days has a slightly swolen belly,any ideas as to what it may be or is it meant to be like that?
Do you mean Zebra Danio (also called zebrafish)?
If so, I have experience with these - if the belly is bigger it's a female. But like Willdrafter said, if it's scales are like that of a pine-cone it could be ill.
A photo would really help if you can get one