Why any fish in a tank seems half alive?

[Ardeus]

This is not a generic question, first of all.

I have dived in marine and fresh water environments hundreds of hours and I have had fish tanks since I was a kid and I noticed this in all my tanks. But you don't have to dive to notice this, you can see it too in nature docs.

Even in tanks where the fish have more space than what they use in the wild, I notice the same thing: the fish have half the vitality than they have in the wild.

That also applies to public aquariums so it can't be just a question of space. In fact, I think I notice it even more in public aquariums.

 

[Reef of Fillory]

I think that a major factor to this behavior is that in our aquariums we don't have a predatory threat to our fish. They don't have to be hyper vigilant in order to survive, and they just swim around waiting for our next feeding. When they are captured, raised and kept in peaceful environments they tend to lose some of their 'natural' fear from predation.

 

[Ardeus]

That may be part of the problem, but it can't be the main cause, because even in situations where there are predators in the tank, you can still notice the lack of vitality.

You also notice it in the top predators too. Just look at sharks in public aquariums.

There is more to it and if we have more hints, maybe there's something more we can do to improve the lives of the fish in captivity.

Even clownfish seem completely different fish in the wild.

 

[jcdeng]

psychological, look at the lions in zoos.

 

[Ardeus]

I thought about the fact that most fish were removed from the wild, but captive bred fish act in a similar way.

In Lisbon there's a huge reef tank, and the fish also move very slowly when compared to the fish in the wild.

See them here at around 16:10

 

[Reef of Fillory]

The tank you show is still very small compared to an entire system, and lacks predators. The suggestion of observing sharks in captivity brings many other factors in to the equation including the fact that the enclosures that sharks are kept in [in very large aquariums] are still small fractions of most sharks daily travel. For example, Shedd's aquarium in Chicago has a 90,000 gallon tank and all those sharks can do is swim in circles around the outside edges of the tank. While I was there just before feeding time, it took the sharks maybe 45 seconds to do a loop around the aquarium. No need or space for natural behaviors, and they are grouped with other animals that they may well never encounter in the wild. They are trained to be fed everything they need on a set schedule and to be complacent and wait for the next feeding.