In Why don’t fish crash into the side of the fishbowl?, I guess the thing that goes unsaid is why (some) fish have eyes on the sides. To see more of the panorama, right? To avoid predators?
Most fish have the eyes mounted on the side of the head, which gives them a very wide field of vision. This is, as you say, good for detecting predators, and also for detecting food at a distance.
The benefit of having eyes mounted on the front of the head, facing forward, is that it permits stereoscopic vision and more accurate depth perception (although at the sacrifice of a wide field of view). This arrangement is found mainly in predators (e.g. mammalian carnivores, birds of prey), which need to make fine assessments of the distance to their prey. It is also found in primates, undoubtedly as an adaptation to being able to judge the distance to the next limb when leaping about in trees.
The reason that this arrangement is not found more often in predaceous fish may be because of the need for streamlining. Most of these predators need to accelerate rapidly in order to catch their prey. Having eyes mounted in front perpendicular to the direction of movement would necessarily slow them down. This consideration is much more important in the aquatic environment, because water is much denser than air and provides much greater resistance to rapid movement. It is also possible that a fish’s pressure sense enables it to determine the distance to a prey item sufficiently well that it makes stereoscopic vision less necessary.
I appreciate your zoological explanation for fish not bumping into the walls of their tank. However, stereopsis and depth perception aren’t exactly the same thing. The following is an exerpt from the American Academy of Ophthalmology’s Basic and Clinical Science Course: “Stereopsis and depth perception should not be considered synonymous terms. Monocular clues contribute to depth perception. These monocular clues include object overlap, relative object size, highlights and shadows, motion parallax, and perspective. Stereopsis is a binocular sensation of relative depth caused by horizontal retinal image disparity.” etc. blah blah.
The fish in question doesn’t brain himself for the same reason people with one eye don’t run into walls (often). And the same reason cows (also lateral eyed) don’t run into the walls of the barn(often). Namely, depth perception based upon monocular clues.
The most salient monocular clue in the fishes situation would be his own reflection. Even in the absence of the proper lighting setup for a good reflection Mr. Fishy can see the glass for the same reason we can. Though transparent…its not invisible.
By the way speaking of lateral eyed animals. Do you think the Dissociated Vertical Deviation is an atavistic recapitulation of the Dorsal Light Reflex?..Just joking.
Several weeks ago, I went inside my bank and noticed these gorgeous fish on display on the counter. In between the teller “windows” they had what looked like big goblets, each w/one fish in it.
They weren’t moving their fins or anything so at first I thought they were fake, but they were real, and apparently not dead.
The manager told me that they were happy where they were, because they were “betas.”
I don’t know about aquarium fish, but somehow I can’t imagine that they really don’t mind being stuck in such a small space, with absolutely no cover whatsoever, just glass and some colored pebbles.
For the entire time the bank is open, they are there on display in front of strangers, 365 degrees all around, because there’s no wall nearby.
Is this truly something that this type of fish doesn’t mind?
I will be extremely relieved if I am wrong. 
Probably a beta, which don’t mix well with others.
I was once close to a beta, but before I could get up enough nerve to ask this question, he fell in love with my girlfriend and it destroyed our relationship.
How would you feel, sandwiched there between alpha and gamma?
betta 
I knew a couple of Alpha Gammas I wouldn’t have minded being sandwiched between.
RR
I’m well aware that binocular vision and depth perception are not the same thing, and that monocular cues to depth also exist. However, stereopis is much superior to monocular clues in enabling depth perception – which is exactly why animals that require keen depth perception, like predators and arboreal species, have binocular vision.
Nope. Not one of the monocular clues you mention (object overlap, relative object size, highlights and shadows, motion parallax, and perspective) apply to the specific case of detecting a clear flat glass barrier. (And the fact that you had to add the qualifier “often” does suggest that you recognize that monocular cues are significantly inferior to stereopsis.)
While a fish may be able to see its reflection in certain circumstances, in other lighting conditions the glass will in fact be essentially invisible. And this ignores the fact that fish are able to avoid the glass, and other objects, even in complete darkness, as I mentioned in the case of blind cave fish.
This seems to be a bit of sensory chauvinism on your part. Humans, being visual organisms, often assume that vision is just as important to other organisms, and that they perceive the world the same way we do. Why should a fish rely on monocular cues – most of which don’t work on glass, or in the case of reflection, only work in certain circumstances – when it has a perfectly good pressure sense to tell it exactly where the glass is?
I’ve always thought that fish had more sense than to bump into the glass of their bowls or tanks, which was more than I could say for the customers in the W. T. Grant store I worked in, in 1972 in Torrance.
As for other critters, I got a good idea of what makes them tick, or rather what doesn’t: Once at Grant’s a parakeet escaped from a cage and headed straight for the front window, which the poor birdie must have mistaken for an open space (the same thing as flies in a house constantly bumping against a windowpane). The bird didn’t know anything about the window and smacked into it–and fell like a rock!
I might also mention that, with regard to the question I answered in the staff report itself, the betta (assuming it was a male) is obviously not reacting to his own reflection when he avoids the glass.
As the original question stated:
Male bettas, also known as Siamese Fighting Fish, are hyper-aggressive and will attack their own reflection in a mirror, as shown in the next-to-last photo on this page. So that if a male betta is actually seeing his own reflection, he is more likely to attack the glass than avoid it. However, in a curved bowl any reflection may be so distorted (as in a fun-house mirror) that the fish will not recognize it as another fish.
Bettas are in fact adapted to live in small pools of relatively stagnant water, and in their native region of Southeat Asia often live in rice paddies. They have an adaptation called a “labyrinth system” that enables them to extract oxygen from air, rather than just relying on gills to take oxygen from water. However, although they are more capable that most fish of being able to survive in small bowls, this is not really good for them and larger tanks are much better.
[FONT=Century Gothic]Thanks for the info - I’ll have to investigate this labyrinth system. I am slightly reassured by your answer, but still troubled by this practice of keeping them in what looks like a large brandy snifter.
Even with the additional source of oxygen, there still is the issue of space. These were not “small bowls.” These fish couldn’t swim more than one body length. I had seen the same setup in a young girl’s room, so now I wonder if they are displayed this way regularly, meaning that people who buy them will think this is perfectly acceptable.
I hope Colibri can tell me that my fears are unfounded. I’d be delighted to be wrong in this case.
I guess that various kinds of animals do have varied comfort zones; cats seem perfectly content to spend days in the hospital in small cages. Maybe any claustrophic bet(t)as were deselected so only those that don’t mind it have reproduced.
Oh, and also the lack of any hidey holes or vegetation to hide in. I must say, I am not aware of any critters that can tolerate not having somewhere to get away from it all. Well may sponges & tunicas, although at least they’re inside a community, which is a haven of sorts.
/FONT]
Well, I can’t say I’m an expert on fish mental health. I don’t know how much such a set up would mess with a betta’s psyche, such as it is. However, I personally would not recommend it. Even if a betta is capable of surving in such a small container, it undoubtedly be more comfortable in something larger, and with weeds or other shelter in which to hide.
I must tell you that I am in a perfect position to discuss the effects of a betta’s tank size on his behavior (mostly it is only the males sold as pets because they have longer, brighter fins.)
At the moment I am caring for two bettas: mine, who is named Polychrome, and the betta belonging to my neighbor next door, who is named Scarlet (the fish, that is, not the neighbor. The neighbor is named Devon and she is visiting family for a few days, so someone had to take of her fish and since she knew I had a betta, she brought him over here.)
Anyway. Polychrome’s bowl is about the size of a basketball, I would guess, or maybe a bit bigger. It is much larger than the bowls that bettas are sold in at the pet store, and it’s made of a pale purple glass. I have some black pebbles at the bottom, and a fabric plant, and a little bubbler in there. I know that bettas don’t need the bubbler, since they can breath surface water, but he seems to like it because he swims through the bubbles a lot.
Scarlet’s bowl is the common sort of goldfish bowl that you could get at any petstore (sort of round with flat sides, like this . It is much smaller than Polychrome’s, and it doesn’t have a plant or anything in it except some gravel at the bottom. Also, I don’t think the water has been changed in a while, because the level is really low, like it’s evaporated, and it’s kind of cloudy. I am going to clean it tomorrow.
Polychrome is much more active than Scarlet. Scarlet just sort of floats at the bottom of his tank, while Polychrome swims around and responds when I come over to the bowl. He’ll swim to the top and nibble my finger if I hold it right above the water. Scarlet just ignores me.
Also, Scarlet seems to be much fatter than Polychrome. When bettas eat too much, their abdomens swell, and Scarlet has a big fat belly. I know that Devon usually gives him two pellets of betta food a day, while I give Polychrome three, so I can only assume that Polychrome is slimmer because he gets more exercise.
So I can only conclude that bettas like bigger bowls, with interesting things in them. I know I would.
I dunno, it would seem that you could also conclude that bettas like cleaner bowls. Or maybe one of them is sick.