I always thought keeping a humble fish would be easy - get a tank, fill it with water, and add the fish. Pinch of flakes now and again, and voila! A lovely calming display of the fish lazily swimming around, exploring the sea captain’s chest you artfully placed on the bottom of the tank between waving greenery.

Well, just hold that thought, because it’s not that easy! There are so many things that can go wrong in a tank, you wouldn’t believe it.

The tank must be big enough so they say. You should have at least 24 square inches of water for every 1 inch of fish. However, I researched this and discovered that you can keep goldfish in particular (which is a good starter choice) in a small tank, and here’s why.

Goldfish can grow to the size of their tank it’s true, but it’s a myth that goldfish are destined to outgrow smaller aquariums. Goldfish produce a growth-inhibiting hormone (GIH) that builds up in the water.

When that water is changed all the time, the hormone is removed and the fish continues to grow. A bigger tank helps to dilute this hormone, which is why goldfish tend to get really big in a big tank. But....in a bowl or small tank, that hormone is very concentrated (unless lots of water changes are done all the time), so it limits the fish’s growth.

This means the growth of the fish is stunted, and doesn’t necessarily mean it’s a bad thing, as many goldfish reach a ripe old age of 30-40 years (I must admit mine didn’t live that long!) being healthy but not enormous.

Believe it or not, even one goldfish can produce a lot of…umm…waste, together with uneaten food, and the water will need a suitable filter to keep the water clean and fresh. In addition, you will need to roll your sleeves up and plunge an arm in to keep the insides of the glass free from algae build-up. The importance of clean water in a tank can’t be stressed enough, and cleaning should be done once a week, which means syphoning some water out and topping up with fresh, but even this has pitfalls if the temperatures are not the same, and the water will need to be ‘conditioned’ to ensure the new water isn’t too acidic. If you have gone the easy route with fake greenery, then that will need to be cleaned thoroughly too.

I have had Siamese Fighting Fish too – not at the same time as the goldfish I hasten to add! Commonly known as Betta Fish, they are beautiful creatures and come in beautiful various vibrant colours, but these are tropical fish – and where the goldfish is ok in cold water, these might need temperature control, though maybe in Portugal it would probably only be necessary in the winter. We had two, but being very territorial, they had to be kept apart in a double tank, as they will do as their name suggests – fight, sometimes to the death. They are quite tolerant of not-so-clean water and low oxygen levels too. They can be kept alongside some other tropical fish, such as guppies, neon tetras and ghost shrimp, who all have speed on their side, but the Betta might get a nip from his beautiful tail – you won’t know if they will attack each other until you try!


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