01 of 04
How Fish Swim
Most fish swim by body movements, not fin movements. The fins are mainly balancers, with the exception of the tail fin, which often acts as a final thrusting member, propelling the fish through the water. In normal, medium-paced to fast swimming, the action is initiated at the head end of the fish, and waves pass down the body, culminating in a flick of the tail. The dorsal and anal fins prevent the fish from turning over in the water; the paired fins also perform braking and turning functions.
In slow swimming, and in static balancing in the water, the pectoral fins are used. These fins are usually colorless, so that when the fish is still in the water, their gentle movement is unnoticed. Indeed, in a fish like the Siamese fighter (Betta), these “pectoral” fins must be looked for very carefully, in contrast to the bright colors of the rest of the finnage.
Some fish, particularly some of the African Cichlids and Sticklebacks, normally swim with the pectoral fins rather than the body, but this is an unusual habit and not the norm.
02 of 04
How Fish Balance
The balance of fish is controlled by 3 main factors:
1. The Inner Ear
The inner ear contains (as do most mammal ears) a system of sensitive sacs containing bones, called otoliths, which are balancing organs. The movement of the bones in the sacs tells the brain of the fish about its orientation and movements.
2. The Muscles
The muscles themselves convey messages of position and movement, and it is possible that the lateral line also does so. In a fish, it is likely that only active movements bring forth the inner ear and muscular perceptions. It has also recently been discovered that many fish are equipped with a kind of radar device, the muscles acting as broadcasters of electrical impulses which are reflected from surrounding objects.
3. The Eyes
The eyes are very important in most fish, not merely for normal visual perception, but because the fish so adjusts itself, if possible, that the two eyes receive equal amounts of light. One of the exceptions to this is the Blind Cave Fish, that has evolved in dark caves and has no eyes at all. It “sees” with a unique sense of “radar” similar to a bat in many ways.
However most fish do use the light source as a sense of direction and orientation. This is much the same reaction that causes insects to fly into a light. In the aquarium, the effect of light is seen if the light source entering the tank is not from overhead (an example may be one of the new underwater LED waterproof light tubes). The fish may be observed swimming at an angle, sometimes a very odd sight as they swim in an orientation to the light source as if it were the surface of the aquarium. Continued slanting illumination is said to cause disorders in the fish subject to it, so if you do use submersible lighting for “effect” do not use it instead of overhead lighting, but only as a supplement.
03 of 04
Metabolic Rate and Oxygen Need
The rate at which an animal uses up energy, produces heat and waste products, and consumes oxygen is called the metabolic rate. An understanding of the factors which modify it is of primary importance to the aquarist.
Since the fish are cold-blooded, they differ fundamentally from mammals in that they have an increased metabolic rate as the temperature rises and are hungriest when warm. Humans consume a great deal of energy, which is in various food and drinks, in maintaining body temperature constant and normally well above that of the body’s surroundings. A fish, on the other hand, doesn’t have a warming mechanism to do this but merely obeys a basic chemical law which causes the body processes to go faster, the higher the body temperature becomes due to the temperature of the water that surrounds the body itself. Thus a fish turns food into energy at a much greater rate in warm water than in cold water.
Another factor influencing the metabolic rate is activity. A resting fish consumes less energy (food) than an active fish. The higher the temperature, the more energetic a fish tends to be, so that an elevated temperature acts doubly in causing greater energy consumption in most species – the fish is using more energy not only because it is warmer but also because it has to swim more to catch and to consume and digest more food. This action has an upper limit, however, and probably determined by the lowered solubility of oxygen in warmer waters. Thus, at about 80F, the average fish reaches its maximum oxygen consumption and maximum appetite. This is also the prime temperature to induce breeding activity in most species, and to induce quickest birth cycle in livebearer species.
A further factor influencing metabolism is age. Young fish are growing relatively faster than older fish and also they use up oxygen and foodstuffs faster per unit of body weight. There are no exact recorded measurements for fish that I know of, but if they are anything like birds and mammals in this respect the difference is one of several hundred percent – I.E. an ounce of adult barbs needs only a fraction of the oxygen per minute that an ounce of young barbs needs.
One final important factor to consider, especially in livebearers, is sex and pregnancy. Gravid female livebearers need a good deal more oxygen than even younger fish or the males and will suffocate first in an overcrowded tank containing adults and young. This is because they are breathing for their young as well as for themselves.
04 of 04
A Note on the Labyrinth Fish
The Labyrinth Fish or Anabantid are bubble nest builders, but beyond this they can actually breath oxygen directly out of the air by use of an organ called the labyrinth. The habit if building bubble nests is a similar adaptation derived from their breathing air. The bubble nest is built from a combination of mucus and air forming bubbles that float on the surface, and the eggs of the fish are deposited within the nest.
The male watches carefully over the eggs and later the young when they hatch. Now here is the problem for beginning breeders, most Labyrinth Fish species are relatively easy to breed, the fish do all the work, but they lay and the male hatches out literally thousands of fry.
Once those thousands of fry leave the nest, the oxygen requirements are so steep that if the breeder does not have a very large and well aerated tank, the fry quickly suffocate and die. In nature, the nests are built in swampy estuaries of streams and ponds, as soon as the fry are free swimming they scatter to the vastness of nature.
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