In a shoal of one hundred fish, each individual has only a one-in-one-hundred chance of being killed during an attack. This benefit, as with foraging success and mate acquisition, increases in value as the size of the shoal increases and maybe another reason why fish choose large shoals over small shoals. Another important consideration, with respect to the anti-predator benefits of shoaling, is the confusion effect. This phenomenon is associated with the high degree of similarity between members of a shoal.
In theory, the confusion effect suggests that a predator, confronted with a large group of similar-looking individuals, experiences perceptual confusion, which slows the attack. This may occur because the predator has difficulty identifying a single individual fish to attack. For example, imagine a bright yellow fish shoaling with a group of grey fish. An approaching predator will be drawn to the yellow fish as it stands out in stark contrast to the rest of the group.
Since fish change shoals on a regular basis, individuals are often faced with the decision of which shoal to join. Joining the wrong shoal could have disastrous consequences. Most shoaling studies, however, indicate that fish are very good at choosing shoalmates with similar characteristics to themselves. The study of shoaling behavior is relatively easy. Test tanks like the one used in Fish Cam are aquariums divided into thirds by the addition of two panes of glass.
It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. A recent answer suggests that some aquarium fish are 'shoal fish' and that there is a minimum number that should be included in a group when adding to your tank. The term 'shoaling' just means that the fish is normally found in very large groups.
These species are most comfortable when kept with others of the same kind. Keeping them alone or in very small groups is a source of stress for them, and often causes them to become more aggressive or timid than they normally are.
Some of the most common fish in pet stores are shoaling fish: most tetras, corydoras catfish, danios, mollies, guppies, etc. But bear in mind that many anti-social fish are kept in large numbers in pet store tanks, but should be kept alone or in very small groups at home -- common plecos are an example of that. So "how many should I keep? There's no magic minimum number; for some of these species, you'd find thousands in a relatively small area, and you'll never be able to keep that many.
Personally, my own preference is to keep at least a half-dozen or so: I feel like this is enough that they'll see lots of others, and any hierarchy that needs to form can be as complicated as it needs to be. More is always better: the social dynamics get more complicated so you see more interesting behavior, and it's really neat to watch a tight shoal dart from one side of the tank to another. My bare minimum is three, since I figure each fish can see "that guy" and "that other guy".
I wouldn't be comfortable keeping this few long-term, but it's what I'd encourage someone to consider if they already have one shoaling fish but not much tank space. Technically speaking, a shoal is a large social group of fish, though not quite what we'd call a school.
The difference is that a school of fish acts more or less in unison , while a shoal is not quite so organized. In the aquarium hobby, you'll often hear the two terms used interchangeably despite the distinction; offhand I'd say most freshwater species in the trade tend to shoal rather than school. Not all social fish are shoaling fish, and in these cases more is not always better. Some species do best in mated pairs or harems one male, several females , and any others that stray into their territory are not tolerated.
Additionally, their diet should include either live or frozen bloodworm, brine shrimp or mosquito larvae at least once a week. Make sure that the bottom-dwelling catfish, gobies and cichlids all get their share of the food. Once settled, these fish will usually rise off the substrate to snatch food in mid-water. Small sinking pellets, wafers and tablets, delivered if necessary with a large turkey baster, will ensure that enough foods do reach the fish on the bottom.
This method can also be used to deliver live and thawed frozen foods to the gobies and even the eartheaters will relish small foods rather than large foods. Some fresh lettuce and blanched zucchini will be appreciated by the silver dollars but will also be nibbled on by several of the other species. Avoid overfeeding, as uneaten food spoils the water. It is better to feed smaller quantities that can be eaten within three or four minutes, two or three times a day.
Within a day or so, it is easy to judge how much food to offer so that all the fish get adequately fed without leaving excess to rot in the tank. South America provides dozens of small colorful fish that are suitable for life in the aquarium. This setup offers enough accommodation for neon tetras and red serpae tetras, two colorful, active, mid-water swimmers that enjoy swimming in a shoal, leaving the substrate for a shoal of bottom-dwelling corydoras.
Fish should be introduced in the order they are listed below. Neon tetras Paracheirodon innesi are one of the most popular freshwater tropical fish. These slender fish have a vivid, narrow, iridescent blue-green stripe running from the eye to the adipose fin and a broader red stripe running along the caudal peduncle to the base of the anal fin. They are a strikingly pretty fish. These fish are self-assured when kept in a shoal of 10 to 12 fish. Peppered corydoras Corydoras paleatus are stocky armored catfish.
Their scaleless pink skin on the flanks is decorated with dark-green patches, leaving a pale under side. Elongated sharp first rays in the dorsal, pectoral and adipose fins protect the catfish but also get caught in fishnets. Corydoras do appreciate living in a group of at least five to six fish on the substrate level. Red serpae tetra Hyphessobrycon eques are deep-bodied fish with a generally reddish-brown body and a dark band behind the gills.
They sport a tall black dorsal fin, and the long-based anal fin and the forked caudal fins are generally deep red, making for a rather eye-catching fish. A shoal consisting of six to eight fish should keep their boisterous behavior, which sometimes includes fin nipping, under control. All three species of small South American fish should do well in a gallon aquarium, measuring 30 inches long, 12 inches wide and 18 inches tall. This kind of enclosure can sometimes be bought as a starter kit that includes a watt aquarium heater, an internal power filter and LED lighting.
A 3-inch substrate bed of smooth, small-grain gravel will give plants a chance to root. Taller Amazon sword plants Echinodorus amazonicus interspersed with water milfoil Myriophyllum spp. Shorter plants suited for the foreground include hair grass Eleocharis spp. Strategically placed pieces of bogwood can be used to offer hiding places for the catfish. These three species should work well in this aquarium, where the tall Amazon swords and bog wood offer cover to fish that want to take a break from running with the shoals.
While neon tetras tend to have orderly shoals when not feeding, serpae tetras seem to dance around with lots of obvious and interesting male-on-male interactions to watch and enjoy. The corydoras are mobile on the substrate, except when they dash to the water surface for their gulp of air.
Tiger barbs Puntius tetrazona are popular shoaling fish. Their pink, deep-bodied shape is decorated with four distinctive vertical black stripes. Southeast Asia is a haven for fish that are suitable for the aquarium. New species are still being discovered as Myanmar opens up, but for this aquarium we will stick to the old faithful, the colorful zebra danio and the spectacular tiger barb for the mid water.
A relative newbie, the chain loach is a lovely fish for the substrate. Zebra danios Brachydanio rerio are torpedo-shaped fish that are silvery gold, with five metallic-blue horizontal stripes, which run from behind the gills into the tail.
The anal fin is also similarly stripped. This stunning body coloration contributes to the great popularity of this fish. Both male and female only reach a size of 2 inches.
A dozen of these inexpensive danios are a good starting point for your Southeast Asian aquarium. Dwarf chain loaches Yasuhikotakia sidthimunki are slightly stocky torpedo-shaped fish. They are gold colored, with two dark horizontal bands on each side, which are overlaid with six to nine vertical bands, forming an attractive chain-like pattern. Dwarf chain loaches are very active but peaceful bottom-dwelling fish.
They do well in a group of six to eight and enjoy moving around in a shoal. An orange snout, as well as orange pelvic and caudal fins, make for a handsome fish that can grow to 3 inches long. They are lively characters, with a reputation for fin nipping, but this can be managed when they are maintained as a shoal of eight to nine fish. For the Southeast Asian shoaling fish, a larger gallon aquarium, measuring 36 inches long, 12 inches wide and 20 inches tall, with the usual 3-inch bed of smooth gravel is ideal.
A good selection of Asian plants are available that include Java fern Microsorum pteropus growing from a rhizome bound to bogwood pieces interspersed with Hygrophila difformis and Rotala rotundifolia. Using shorter-growing Cryptocoryne walkeri for some sections provides a relatively large space for the shoaling fish to swim. The three species of shoaling fish would be expected to lead a peaceful coexistence in this furnished aquarium setup that provides plenty of cover.
Tiger barbs can be fin nippers, but with no long-finned fish to trouble in this aquarium, the males in particular stay busy by maintaining their hierarchy within the shoal. The zebra danios are also a lively fish that fit well in this aquarium while the shoaling chain loach move around gracefully on the substrate and under the bogwood in search of food.
Congo tetras Phenacogrammus interruptus are playful in a shoal. Africa does have a good selection of barbs and tetras in its rivers and lakes, but only a few species are available regularly in the tropical fish hobby. Fortunately, Congo tetras are regularly available as are a few other larger tetras, but it is worth searching for the smaller yellow-tailed Congo tetra. Young, shoaling dwarf butterfly cichlids make an interesting addition for the substrate.
Yellow-tailed Congo tetras Alestopetersius caudalis can grow to 3 inches total length and are a beautiful pale-yellow fish. A brown stripe bordered in gold runs down its midline and extends into the caudal fin.
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