Such shifts are triggered by changes of activity from feeding, resting, travelling or avoiding predators. Koi keeping is not a belief system; it is applied science with a touch of artistry. Comment Post Cancel. It happens when there is warmer water towards the surface or a warm rain. I have seen a streight line of some twenty fish swimming in a large circle.
There is no apparent leader they just randimly get behind each other leaving a space of a fish length between them. The duration of this swim lasts about 30min then they break up gradually a few swiming away at a time. Regards Eugene. Besides the laterla line there are a set of bones at the back of thier heads called Weberian ''something''..
Right Dick, although the koi has many systems and techniques to 'keep in touch with the outside world' , the lateral line is the system that 'spaces the fish in a formation or within proximity to one another. Anyone know how that one works? Just going by your name for them, JR, I'd say it sounds tied in to the stress response of increased blood flow to the skin. Seeing a group of fish swimming in unison is probably the dream of all choreographs. It looks so perfect!
How is this achievement possible? First, it is important to understand the difference between a shoal and school of fish. Sometimes people don't really know what is the distinction. This two terms are routinely used in marine life books and in bio-conversation media, and both of them are used to define a behaviour of a group of fish. A group of fish staying together is called shoal when its purpose is to avoid being eaten by a bigger predator.
A shoal is a group of individuals congregating together to benefit from "safety in numbers" but not moving or behaving in unison.
The reason they stay in a group can be as well for social reasons: meet a female or a male partner, or to find food. Richard writes for several magazines on topics as diverse as scuba diving, travel and wildlife. Save my name, email, and website in this browser for the next time I comment. General Discussion. Reefs for Beginners. Advanced Reefs. Nano Tanks. Tank Threads. They have large antennae see photo below left.
When they spread their antennae they can sense the pressure wave from an approaching fish and jump with great speed over a few centimeters. If copepod concentrations reach high levels, schooling herrings adopt a method called ram feeding. In the photo below, herring ram feed on a school of copepods. They swim with their mouth wide open and their opercula fully expanded. The fish swim in a grid where the distance between them is the same as the jump length of their prey, as indicated in the animation above right.
In the animation, juvenile herring hunt the copepods in this synchronised way. The copepods sense with their antennae the pressure-wave of an approaching herring and react with a fast escape jump. The length of the jump is fairly constant. The fish align themselves in a grid with this characteristic jump length.
A copepod can dart about 80 times before it tires. After a jump, it takes it 60 milliseconds to spread its antennae again, and this time delay becomes its undoing, as the almost endless stream of herrings allows a herring to eventually snap the copepod.
A single juvenile herring could never catch a large copepod. A third proposed benefit of fish groups is that they serve a reproductive function. They provide increased access to potential mates, since finding a mate in a shoal does not take much energy. And for migrating fish that navigate long distances to spawn, it is likely that the navigation of the shoal, with an input from all the shoal members, will be better than that taken by an individual fish.
Forage fish often make great migrations between their spawning, feeding and nursery grounds. Schools of a particular stock usually travel in a triangle between these grounds. For example, one stock of herrings have their spawning ground in southern Norway , their feeding ground in Iceland , and their nursery ground in northern Norway. Wide triangular journeys such as these may be important because forage fish, when feeding, cannot distinguish their own offspring.
Capelin are a forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, they graze on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat krill and other crustaceans. The capelin move inshore in large schools to spawn and migrate in spring and summer to feed in plankton rich areas between Iceland , Greenland , and Jan Mayen. The migration is affected by ocean currents.
Around Iceland maturing capelin make large northward feeding migrations in spring and summer. The return migration takes place in September to November. The spawning migration starts north of Iceland in December or January. The diagram on the right shows the main spawning grounds and larval drift routes. Capelin on the way to feeding grounds is coloured green, capelin on the way back is blue, and the breeding grounds are red. This theory states that groups of fish may save energy when swimming together, much in the way that bicyclists may draft one another in a peloton.
Geese flying in a Vee formation are also thought to save energy by flying in the updraft of the wingtip vortex generated by the previous animal in the formation.
It would seem reasonable to think that the regular spacing and size uniformity of fish in schools would result in hydrodynamic efficiencies. Landa argues that the leader of a school constantly changes, because while being in the body of a school gives a hydrodynamic advantage, being the leader means you are the first to the food.
Schooling predator bluefin trevally size up schooling anchovies. It is commonly observed that schooling fish are particularly in danger of being eaten if they are separated from the school. Template:Externalimage Predators have devised various countermeasures to undermine the defensive shoaling and schooling manoeuvres of forage fish. Some of these predators, such as dolphins, hunt in groups of their own.
One technique employed by many dolphin species is herding , where a pod will control a school of fish while individual members take turns ploughing through and feeding on the more tightly-packed school a formation commonly known as a bait ball. Corralling is a method where fish are chased to shallow water where they are more easily captured.
In South Carolina , the Atlantic bottlenose dolphin takes this one step further with what has become known as strand feeding, where the fish are driven onto mud banks and retrieved from there. During the sardine run , as many as 18, dolphins, behaving like sheepdogs, herd the sardines into bait balls, or corral them in shallow water. Once rounded up, the dolphins and other predators take turns ploughing through the bait balls, gorging on the fish as they sweep through.
Seabirds also attack them from above, flocks of gannets , cormorants , terns and gulls. Some of these seabirds plummet from heights of 30 metres feet , plunging through the water leaving vapour-like trails, similar to that of fighter planes. They have air sacs under their skin in their face and chest which act like bubble-wrap , cushioning the impact with the water. The sailfish raises its sail to make it appear much larger so it can herd a school of fish or squid.
Swordfish charge at high speed through forage fish schools, slashing with their swords to kill or stun prey. They then turn and return to consume their "catch". Thresher sharks use their long tails to stun shoaling fishes. Before striking, the sharks compact schools of prey by swimming around them and splashing the water with its tail, often in pairs or small groups.
Threshers swim in circles to drive schooling prey into a compact mass, before striking them sharply with the upper lobe of its tail to stun them. Spinner sharks charge vertically through the school, spinning on their axis with their mouths open and snapping all around. The shark's momentum at the end of these spiralling runs often carries it into the air. Some whales lunge feed on bait balls.
This generates the water pressure required to expand its mouth and engulf and filter a huge amount of water and fish. Lunge feeding by the huge rorqual whales is said to be the largest biomechanical event on Earth. Fish schools swim in disciplined phalanxes, with some species, such as herrings, able to stream up and down at impressive speeds, twisting this way and that, and making startling changes in the shape of the school, without collisions.
It is as if their motions are choreographed, though they are not. There must be very fast response systems to allow the fish to do this. Young fish practise schooling techniques in pairs, and then in larger groups as their techniques and senses mature. The schooling behaviour develops instinctively and is not learnt from older fish.
To school the way they do, fish require sensory systems which can respond with great speed to small changes in their position relative to their neighbour. Most schools lose their schooling abilities after dark, and just shoal. This indicates that vision is important to schooling. The importance of vision is also indicated by the behaviour of fish who have been temporarily blinded. Schooling species have eyes on the sides of their heads, which means they can easily see their neighbours.
Also, schooling species often have "schooling marks" on their shoulders or the base of their tails, or visually prominent stripes, which provide reference marks when schooling, [44] similar in function to passive markers in artificial motion capture. However fish without these markers will still engage in schooling behaviour, [45] though perhaps not as efficiently.
Other senses are also used. Pheromones or sound may also play a part but supporting evidence has not been found so far. The lateral line is a line running along each side of the fish from the gill covers to the base of the tail. In laboratory experiments the lateral lines of schooling fish have been removed. They swam closer, leading to a theory that the lateral lines provide additional stimuli input when the fish get too close.
It uses receptors called neuromasts, each of which is composed of a group of hair cells. The hairs are surrounded by a protruding jelly-like cupula , typically 0. The hair cells in the lateral line are similar to the hair cells inside the vertebrate inner ear, indicating that the lateral line and the inner ear share a common origin.
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