FishProfiles.com Message Forums

Why do some fish need to school? I mean there are many fish that don't need to - why can they surivive on their own when others can't.

Obviously in the wild it would be for defencive reasons, but if in a relatively small community tank with no threat, why do you still need to buy some fish in groups of 6+ (or whatever it may be).

*defensive

I would think it's just because their little brains are wired that way. If they are wired to be in a group, it seems logical that they would get stressed if the group is not there. Threat or no threat.

I would guess for the above mentioned.

Also, for the same reason a newborn always wants, relies and trusts its mother. The fish that school are generally small, so they rely and trust on other fish of their kind to keep company and raise defense. Plus, remember in the wild if you travel in a school, you have a better chance of not getting eaten because there are so many more fish they may be eaten(may be a bad example). "Power in numbers"

But i would say beetledance summed it up. Thats the way it always has been in nature, so thats why it's the way it is today, and will most likely be in the future as well.

Security. The individual fish is safer from predators in a group.

"I am a believer in punctuality, though it makes me very lonely" EV Lucas

Fish are also very social. Some fish are solitary, but they still communicate with everything else in the tank. I guess a school is like "mess with me and you mess with my friends." Either that or its to give off the illusion that it is a much bigger fish.

Inky

In the wild it would be security, company, also some hunt in packs (schools) by circling their prey. With my Cardinals in the 11g tank they would not come out of hiding until I added more and within minutes they were all out from their hiding places.


Have a look in [link=My Profile] http://www.fishprofiles.com/forums/member.aspx?id=1935[/link] for my tank info

Look here for my
Betta 11Gal Desktop & Placidity 5ft Community Tank Photos

Keith

Near enough is not good enough, therefore good enough is not near enough, and only your best will do.
I VOTE DO YOU if not WHY NOT?
VOTE NOW VOTE NOW

I noticed the same phenomenon with my Cardinals.

With a shoal of 6, they were somewhat timid. Now, with a shoal of 12, they're bold and inquisitive. Previously I'd have to go searching for them, whereas now they're at the front of the aquarium most of the time on the lookout for food and engaging in what I suspect is the kind of sparring that eventually leads to spawning behaviour.

Mind you, not all shoaling fishes are small. Pacus are big beasts - they tip the scales at around 60 lbs each fully grown - yet in the wild they cruise around in big shoals. And they're herbivores too. A 60 lb fish isn't necessarily going to be in much danger from predators other than big ones such as Spectacled Cayman. Admittedly its native waters are populated with some impressive predators - apart from the aforementioned Cayman, there are big catfishes in there such as the giant Piraiba that reaches nine feet in length, and the enormous Arapaima could probably swallowe a Pacu if it was minded to, but other than those monsters, most of the predatory fish you'll find in those waters are smaller than the Pacus. Fishes such as Piranhas, Trahiras (with the exception of the 30-inch Hopllias lacerdae with gin-trap jaws) and Cichlia ocellaris are all predators that are smaller in body size than the Pacus.

While juvenile Pacus are under threat from those fishes, adult Pacus are big enough not to be considered food. But they are shoaling fishes too. Which does beg the question of what protection they need from all but the real monsters in their home waters!

However, social factors almost certainly come into play too. While shoaling is an effective defence against predation, it makes other aspects of fish life easier too. Such as finding a mate. Not difficult to find a mate if you're in a gang of 20,000 or so of your own kind! Plus, even if you ARE big like a Pacu, and have few natural enemies, all of those watching pairs of eyes come in handy if one of those few enemies DOES turn up.

Another exception is the Barracuda. This is a powerful predatory fish that reaches six feet in length. But it hunts in packs. Presumably to maximise 'firepower' when on the hunt, so to speak (and presumably the reason why Piranhas are also group hunters). Mind you, in the case of the Barracuda, while it too has few natural enemies, it does have some spectacular potential predators - Great White Sharks that reach 28 feet in length spring to mind quite readily!

Another shoaling exception is Pterois volitans, the Common Lionfish. These fishes will hunt in packs and co-ordinate their activities intelligently to acquire prey. They also have the advantage of being protected against predation themselves by those nice venomous dorsal spines! However, I suspect that they hunt in packs because they're somewhat slow moving - that elaborate finnage creates a lot of drag, and means that they can't 'sprint hunt' in the same manner as the streamlined Barracuda. So in their case, teamwork is a solution to their performance limitations. They replace speed and streamlined efficiency with intelligent teamwork in herding potential prey fishes and cornering them. And believe me, Lionfishes are seriously intelligent fishes - anyone who has kept them for any length of time will recognise their powers readily!

However, it's safe to assume that for whatever reason, if a fish is a shoaling species in the wild, it'll be a lot happier being allowed to shoal in an aquarium. One of the most spectacular displays I ever saw was a dozen Regal Lionfishes in an aquarium at Liverpool Museum (prior to the refit - their Lionfish aquarium is now more diverse) and they were truly awesome to behold. However, not everyone can devote 1,000 gallons upwards to such a display!


Panda Catfish fan and keeper/breeder since Christmas 2002

Pretty much summed up there, but think
Would you rather live in solitary confinement or with friends for your whole life?
Would you prefur to be with others when the 'big bully' came along?

Basically, ALL captive animals still retain their wild instincts, and if your instinct is to shcool, then you'll school.

From my Rummynose Tetra, i noticed, that they are more active & less frightened from the Angels, when they are in a schoal of 16, as they are now. Before, when they where 6 or 8, they where more afraid to leave the bottom part of the tank & only came out to eat.


http://uk.pg.photos.yahoo.com/ph/s8xi5heh/my_photos
http://www.geocities.com/s8xi5heh/classic_blue.html
http://groups.yahoo.com/group/buzaqq/
http://www.deathbydyeing.org/

http://www.flickr.com/photos/corydoras/
Member of the Malta Aquarist Society - 1970.
http://www.maltaaquarist.com

I also heard somewhere that one of the reasons it is hard to transport tetra, especially rummynose is because they release a chemical into the water that warns the rest to get stressed and run away. In a bag this is potentially deadly because the build up would be intense. It is also interesting that tetra shoal's are not just for there own benefit. In researching my Upper Amazon Basin Biotope I have learned that most apistogramma wont leave the comfort of there hiding spots without tetra there that tell them weather or not it is safe to leave there respective caves. So it is interesting from a purely scientific standpoint that the shoaling isn't just for the benefit of the shoaling fish.

There is a sort of collective intelligence aspect to schooling as well. Many schooling fish will individually play a confidence game; in that, a single fish will move a few inches away from the pack, but unless the rest of the pack comes with the individual, the individual will usually hurry back. In this way, the entire school receives information about threats and the like.

If a single fish went forward to inspect a predator, chomp. But, if several fish all come forward, maybe one of them gets attacked, but the others in this scouting party make it back so the entire school receives the information about the threat. In this way, schooling fish approach a predator in short, cautious stages.

There was a rather famous experiment in which the researcher set up two mirrors behind a tank (Milinski 1987). A straight reflecting one and a reversing mirror. When an individual fish from a school was in the straight reflecting tank, it always saw its reflection coming with it, so it was remarkably emboldened to keep going forward. On the other hand, in the reversing mirror, the brave fish always saw its reflection retreating, so it always ran away.

The funny thing is that evolution has really developed an entire population of cowards... again the brave fish gets too close to the predator, and well CHOMP. On the other hand, each schooling fish takes on its small little share of the risk because the information (how aggressive or hungry) about the potential predators is preferred to pure defection.

p.s. for a lot more information about this really interesting phenomena, look up game theory and specifically the tit-for-tat strategy. There are many, many more examples from nature, like vampire bats that will share blood back in the caves, and examples from economic theory as well such as OPEC quotas.