I sent an email to the CATSA here is the reply:
On behalf of the Canadian Air Transport Security Authority (CATSA), we thank you for your e-mail dated November 26, 2012, in which you enquired about traveling with a pet fish.
When traveling from a Canadian airport, permitted and non-permitted items are regulated by Transport Canada and are enforced by pre-board screening officers. According to Transport Canada regulations, a pet fish is permitted in both carry-on baggage and checked baggage. As with all items in your possession, your pet fish will need to be screened, however the container transporting the fish in water is subject to the 100mL liquids, aerosols and gels restrictions. Water for transporting a fish is not exempt.
Please note that if the glass cases contain liquid, passengers are permitted to bring liquids, gels and aerosols through security screening at Canadian airports provided that the items are packaged in containers with a capacity of 100 ml / 100 grams (3.4 oz) or less, and that the containers fit comfortably in one clear, closed and resealable plastic bag with a capacity of no more than 1 litre (1 quart). The approximate dimensions of a one litre/quart bag are 15 cm by 23 cm (6 in. by 9 in.) or 20 cm by 18 cm (8 in. by 7 in.). One bag per passenger is permitted.
So in this case, you are allowed to bring a fish with your carry on provided the liquid amount is less than 100ml and it fits comfortable into one of the baggies. I know in the US the rules for bringing fish (with carry on) are as follows:
Live fish must be transported in a clear, plastic, spill proof container. In this case, the container may be larger than 3.4 ounces. A Transportation Security Officer will visually inspect your live fish at the checkpoint.
Even if an item is generally permitted, it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. The final decision rests with TSA on whether to allow any items on the plane.
Good to know I guess!