From what I understand you have to know the CITIES status of the exact species you are wanting to acquire. That dictates what sort of certification you need for your fish to cross an international border. If it is for personal aquarium use then there are few restrictions on what you can keep. Check out the Canadian Food Inspection Agency, http://www.inspection.gc.ca They have an online program that allows you to search requirements by entering various details of species, source and end use etc. called Automated Import Reference System (AIRS). If all else fails you can call and speak to an agent and they will advise you. There are lists of "susceptible" species that are restricted and lists of species that are banned from import. By susceptible it refers to that species being susceptible to certain diseases that could be a threat to our native cultures and they would have to be certified free of those diseases and a guarantee that a specific protocol would be followed after their arrival before they could be imported.