Swimming, Balance, Oxygen and Food Consumption in Fish

How Fish Swim

Most fish swim by body movements and fin movements. The fins are mainly balancers, except for the tail fin, which 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 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 splendens), 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, usually swim with the pectoral fins rather than the body, but this is an unusual habit and not the norm.

How Fish Balance

3 main factors control the balance of fish:

1. The Inner Ear - The fish's inner ear contains (as in 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 essential in most fish, not merely for normal visual perception, but because the fish adjusts its body, if possible, so 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 “radar” sense, 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.

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 that modify the metabolic rate is of primary importance to the aquarist.

Since fish are cold-blooded, they differ fundamentally from mammals in that their metabolic rate increases as the temperature rises and are hungriest when warm. Humans consume a great deal of energy, which is supplied by foods and drinks, in order to maintain a constant body temperature that is often well above the temperature of the body’s surroundings.

A fish, on the other hand, doesn’t have a warming mechanism to do this but merely obeys a fundamental 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 higher rate in warm water than in cold water.

Another factor influencing the metabolic rate is activity. A resting fish needs 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 higher 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 is probably determined by the lowered solubility of oxygen in warmer waters.

Thus, at about 80 degrees F, 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 the 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.

Remember that female livebearers will need more oxygen than younger fish or males. Keep this in mind as you manage your aquarium.

Oxygen Breathing in the Labyrinth Fish

The Labyrinth Fish, or Anabantids, are bubble nest builders, but beyond this, they can breathe oxygen directly out of the air by use of the labyrinth organ. Native to warm, stagnant bodies of water, they are able to take in air from the surface of the water and hold it in the Labyrinth Organ. Within the labyrinth are many small maze-like compartments of thin bony plates called lamellae. The lamellae are covered with extremely thin membranes, so thin that oxygen can pass through. Blood within the membranes absorbs the oxygen and carries it throughout the body.

Their habit of building bubble nests is an adaptation derived from their breathing air. The bubble nest is built from a combination of mucus and air, to form bubbles that float on the surface, and the eggs of the fish are deposited within the nest. 

The male protects 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 hundreds of fry. 

Once those fry leave the nest, the oxygen requirements are so steep that if the breeder does not have a well-aerated tank, the fry quickly suffocate and die. In nature, the nests are built in swampy streams and ponds and as soon as the fry are free swimming they scatter to the vastness of nature, so they do not remain concentrated in one small space.