A goldfish is often a first pet, because they are deemed to be the easiest. Buy a bowl or a small tank, add a goldfish, buy a pot of food, and there you have it, a trouble-free pet – doesn’t eat much, doesn’t need walking, doesn’t shed hair everywhere – what could be easier?

But the water must be changed every week, as they pee and poo in it, and sometimes don’t eat all the food, and it all sinks to the bottom. And it can’t be just any old water - although not critical, it should have a ph. of between 7.0 and 8.4, with some fancy goldfish needing a temperature of 20c to 23.3c. You may have generously installed a filter system, but this will only get you so far - it will neutralize ammonia and nitrite, converting them to nitrate. It won’t, however, remove all the nitrate from your tank. If you felt lavish, you might have included some plants for the fish to swim round – these will absorb some of the nitrate as fertilizer, but they won’t remove all of it from the tank, so water changes help remove the excess. Changing the water also gives you the opportunity to vacuum the grit or tank bottom and to clean in and around any rocks or treasure chests you put in there.

Seemingly rapid changes in temperature or water chemistry can be harmful, if not fatal, to goldfish. To change the water, the easiest way is to catch ‘Goldie’ in a special net and transfer him to a plastic bag with some of the old water, seal the bag, then almost empty the tank, vacuum the bottom and clean the sides of the tank to ensure there is no green stuff growing on it. Then add clean water to the water left in the tank, which will ensure the fish doesn’t get a shock when returned to its home. Add water conditioner, then the plastic bag with the fish in it should be left to float around in the water for a short while so the temperature of the old and new become the same, then just release Goldie and his bagful of water back into the tank.

But experts say it's best to keep your fish in the fish tank when you clean. Removing them supposedly causes them unnecessary stress, and you run the risk of accidentally hurting them. It’s possible to keep your fish in the tank while you clean, because you don't need to remove all the water to clean the tank properly. Your choice.

Another thing - there are a whole host of illnesses they can get too, from ammonia poisoning, or a bacterial disease called ‘cotton mouth’, sometimes confused with a fungal infection because of the appearance of white or greyish white spots on the fish’s head, though usually this infection starts as a pale area around the head and mouth.

‘Dropsy’ is another disease - something that is usually fatal to fish - swelling of your fish’s abdomen, sometimes causing their scales to stick out. Your fish will appear listless and lose their appetite. If you’re unsure if your fish has Dropsy, quarantine it immediately and take it to your local vet.

Credits: PA; Author: PA;

Fin or tail rot is another thing to watch for - sometimes caused by bullying if there are more than one fish in the tank – then things like stringy white poo, warts, kidney disease, buoyancy problems, and macroscopic parasites. The little devils can also overeat and blow up like little orange balloons – an adult one should be allowed a mere 2 minutes to eat their fill for the day.

And did you know that goldfish have pigment in their skin? This pigment can react to UV light in some fish. So, your goldfish could turn white due to either a lack of sunlight or too much.

They are thought to have very little or no memory, but they apparently do - and scientists have shown that fish can remember and recognise faces. They are good at it too – and can pick a familiar face from up to 44 strange ones.


Marilyn writes regularly for The Portugal News, and has lived in the Algarve for some years. A dog-lover, she has lived in Ireland, UK, Bermuda and the Isle of Man. 

Marilyn Sheridan