Millennium Post


We can make the lives of fish much easier by providing them an environment that replicates their natural habitat


Can the age of fishes be determined?

Scales, bones, fin rays and fish ear bones (otoliths) have all been used to determine the age of fish, since these and other bony parts of fish often form yearly rings (annuli) like those of a tree. Otoliths generally provide the most accurate ages, particularly in old fish.

Do all fish swim in horizontal position?

Most do. The sea horse is among the exceptions. Another is the shrimp fish of the Indian Ocean, which swims vertically in schools of several individuals, its long tube-like snout pointing directly upward. A catfish indigenous to the Nile also swims in the vertical posture.

I have never seen fishes sleep. Do they?

The nature of fish "sleep" is an area of active research. While fish do not sleep in the same way that land mammals sleep, most fish do rest. Research shows that fish may reduce their activity and metabolism while remaining alert to danger. Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest. These periods of "suspended animation" may perform the same restorative functions as sleep does in people.

Yes fish sleep. But it's not sleep as we know it. They don't have eyelids to close, they sometimes do it during the day, they don't show the characteristic brainwave patterns like REM sleep seen in humans, and some, including most sharks have to keep swimming in their sleep.

But fishes do have a period of reduced activity and metabolism which seems to perform the same restorative functions as nocturnal sleep does in humans. Some are more obvious about it than others and actually rest on the bottom or in coral crevices, and parrot fish secrete a mucus "sleeping bag" around themselves before they go to sleep. If you get up quietly in the middle of the night you will find your

goldfish in an almost trance-like state, hovering near the bottom of the tank making just the minimum correcting motions with its fins to maintain its position in the water column. If you put food in when they're like this they take noticeably longer than usual to respond, as if they have trouble waking up.

How many fish can live together?

It is not how many fish can live together but how many fish your tank has the capacity to hold. This will depend on the size and type of fish. Overcrowding a fish tank leads to competition for food and poor water quality due to waste being produced. You will also need to consider which breeds of fish can live together. A good guide is to allow at least 2 litre of water for every 1 cm of fish.

(Views expressed and information provided are personal. Send your questions to

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