What puts people off about fish
Starfish > Coral reef> Systematics> Physiology
anatomy = the doctrine of the structure of living beings, the location and structure of their organs and tissues.
physiology = researches the functions and life processes of the plant and animal body and its individual parts (cells, tissues, organs).
Sensory organs and communication
Fish are generally farsighted, with the greatest sharpness in the middle field. Fish that live in relatively shallow water can see colors.
The limit of the light perception of the fish is approx. 550m depth. Few specialists can still perceive weak residual light at a depth of 1100 m.
Clark's anemonefish - Amphiprion clarkii
Oriental gurnard - Dactyloptena orientalis
Noise, Perception and Generation: Water has a density about a thousand times higher than air. Sound can therefore travel five times faster under water than in the air: 1500m per second. One problem, however, is that the water is constantly in motion and this creates complex sound reflections - on the surface of the water, on thermoclines with different temperatures or salt concentrations, and on the sea floor. It is therefore particularly difficult to communicate over great distances. Dolphins and whales have solved this problem by constantly varying the pitch and frequency of their signals (more information).
Fish can perceive sounds with their lateral line organ and their inner ears. In many fish there is also a connection between the inner ear and swim bladder, so that vibrations of the bladder are transmitted to the ear.
Fish produce sounds in very different ways. They grind their teeth, they swallow air and expel it through the anal opening of the swim bladder, or they rub thorns and fin rays against each other. In some of these mechanisms, the swim bladder acts as a resonance chamber that amplifies the sounds. Such sounds can be so loud that you can hear them even above water. In some fish, special muscles have developed around the swim bladder that contract quickly and produce a drum sound. Since these muscles are only developed by the males in some species, these tones probably play an essential role in courtship and matching.
If the diver holds his breath in order to hear well at all, the following noises can be heard in the water: clicks and grunts (soldier fish and wrasse), growls (gurnards), knocks (angelfish), quick sounds (catfish), drum sounds (Drummers), toktok lutes (anemonefish), croaks (toad fish).
The anemonefish creates various clicking and chirping noises by rubbing its teeth together. Researchers have found that the sounds are made when the hyoid bone lowers and the jaw closes at the same time. The teeth clash together, transferring energy to the jaws, which radiate the sounds into the water.
Some sounds are very loud - the biggest noisemaker in the reef is the pistol shrimp (Alpheidae, actually shrimp), it is only 3 to 5 cm tall, but can generate a noise of 150 to 200 decibels. That is about the volume of a jet taking off!
Defense through poisons and bad tasting substances
Red speckled red mullet (Parupeneus heptacanthus)
Recognizing chemical stimuli is also an important survival factor for fish. Chunks of food, even with low concentrations of toxic substances, are recognized and immediately spat out. When attacked by a fish, some soft corals emit warning substances to which they in turn react sensitively.
Conversely, some fish use chemical substances to protect themselves from predators, such as the parrotfish, which secretes a mucous cocoon at night, which obviously forms an odor barrier. Moray eels cannot smell the sleeping parrotfish now.
Brown = scales / blue = openings of the lateral line organ / pink = muscles / red = nerves
Halfway up the flanks of the fish sit a series of special, openwork scales that run from the head to the tail fin. The visible pores lead to a liquid-filled canal running longitudinally behind the scales, in which the actual sensory organs are located. These sensors are sunk in pits and consist of hair cells that generate a nerve signal when the fine hairy appendages are bent. In this way, water movements can be perceived and their prey and predators can be located.
In addition, some fish have converted the sideline system into electroreceptors and even use this modified system for geomagnetic navigation at times. This means that migratory fish can orientate themselves on the magnetic fields of the earth.
It is difficult to orientate yourself in murky water and at night. Some fish therefore produce electric fields in order to "see". With the help of electrical fields, they can not only recognize conspecifics, possible prey and predators, but are even able to differentiate between materials. The electric field deforms where it meets an object with a different electrical conductivity than water, such as a stone or an animal. There are fish (the Nile pike or elephantnose fish, a freshwater fish) that can perceive a distortion of less than 1 percent. The fish can not only capture the object in three dimensions, but also capture the distance and catalog it in terms of shape and electrical properties.
The sideline organ of these fish has been transformed to acquire the ability to electrolocate. The hair sensory cells (see above) were converted, the hairy appendages were lost and the sensors were stored deeper.
Sharks and rays have receptors that sense the low-frequency electric fields (below 50 Hertz) that surround all living things. The organs (Lorenzini ampoules) are located on the front of the head of sharks. They are fine channels filled with a jelly-like substance that end in ampoules. They are connected to the pores in the skin. With these very sensitive organs, sharks and rays can locate prey buried in the sand. The Nilhecht, on the other hand, perceives the high-frequency fields (100 to several 1000 Hertz) that it generates itself and thus orientates itself in its environment.
White border sky-gazers dug in the sand - Uranoscopus sulphureus
Some species of saltwater fish also generate considerable electrical currents: torpedo and electric rays produce pulses of up to 230 volts and over 30 amps. The kidney-shaped organs for generating the electric shocks are located on both sides of the electric ray's head and are usually quite easy to see. These electrical organs evolved from modified eye muscles.
You can use it to stun your prey or scare off enemies. For example, they lie flat on sole, electrify it or at least disorient it and then eat it. Another tactic is to bury yourself in the sand and then poke up when prey is within reach. The electrical charge is released shortly before the attack. Other species of rays have weakly electrical organs in their tail area that send out pulses of different shapes and durations from species to species. These pulses serve less for stunning prey fish and more for orientation.
The sky-gazer lurks, half buried in the ground, for small fish, which he sucks in by opening his mouth. During this process, the organ fires a burst of pulses (up to 50 volts), but this is not enough to stun the prey. The purpose of these discharges has therefore not yet been clarified, but it is assumed that the animal buried in the sand can locate approaching prey in this way.
Ability of living organisms to actively generate and emit light.
Oxidation of certain phosphors (luciferin from Latin light carrier) under the control of the enzyme luciferase
Many animals emit light (bioluminescence). This ability is particularly widespread among marine animals, where it occurs in almost all groups, from protozoa to marine fish (10-15%). The glow takes place in the cells (intracellularly) in individual light granules and in light tissues (photophores) or organs. Complicated luminous organs therefore often resemble eyes in their structure. That means there is a reflector layer, a lens and even a color filter. Glands can expel a glowing mucus (which has also been observed in sea feathers).
Luminous organs produce cold light (chemiluminescence), which means that over 90% of the energy is converted into light, the rest into heat. The light is generated using chemical processes.
The lantern fish lives in caves during the day. His luminous organs are under his eyes. The organ generates flashes of light. Their frequency depends on the water temperature, time of day and possible predators. Flashes three times per minute when at rest and up to 50 times per minute in case of danger. To switch off the light, he pulls down a lid-like blind. With this flash, prey such as zooplankton and copepods are attracted. In the night he comes out and rises to hunt in higher water layers. Groups of up to 100 animals have been observed.
Breathing and circulation
This oxygen is now distributed throughout the body through the blood. The heart of the fish does most of the work, but the gill muscles also play an important role. Fish have high blood pressure and a relatively low blood volume.
The fish are cold-blooded animals whose body temperature depends on the surrounding water. Only some species like the tuna, the mako shark and the great white shark can maintain their body temperature a few degrees above the surrounding water.Coral fish can tolerate temperatures of 15-33 °. However, they are very sensitive if they are exposed to extreme temperatures or a rapid change in temperatures for long periods of time. Therefore, their distribution is limited to areas where the water temperatures are around 20 °.
Swim and buoyancy
rounded - lanceolate
straight - sickle-shaped
forked - notched
ctenoid - cycloid - placoid
But it is not enough just to swim, the body must not sink at the same time. Most bony fish have therefore developed a swim bladder. This is filled with gas and can be enlarged or reduced as required. This keeps the fish in hydrostatic equilibrium. Many bottom fish have regressed or given up their swim bladders (flatfish, bleached fish, frogfish, many gobies). Cartilaginous fish (sharks and rays) do not have a swim bladder, but instead have a lighter skeleton and an oily liver. The swim bladder also serves as a resonance space to create sounds.
Fish have found various solutions to help the water slide better over their skin surface. The shark has a skin made up of tiny teeth called placoid scales. The body of most bony fish is covered with small bone plates called scales. Along the whole body there are glands in the skin that cover the dandruff with a film of mucus. This mucus also protects against infections, so fish should not be touched underwater. The pattern of fish scales and whether they are pointed or flattened influence the flow resistance.
The blue shark (and other deep sea sharks) has an almost symmetrical, moon-shaped caudal fin, large wing-like pectoral fins and a spindle-shaped body. The symmetrical fins generate more forward thrust than the asymmetrical ones.
Other fish that swim near the bottom, such as the moray eel or the eel, use undulating movements and have developed an elongated, almost eel-shaped body for this purpose. The ray also makes undulating movements, but by hammering the side fins.
Swimming movements eel - mackerel - boxfish - rays
The longhorn boxfish can hover over a buried worm, blow away the sand and then suck it out with its tubular mouth.
The frogfish move on the reflex principle by ejecting water from its gill openings on the hind legs or by galloping if it moves on the bottom.
Anatomy - sense organs and communication - breathing and circulation - swimming and buoyancy
Ampoules - eyes - courtship - barbels - bioluminescence - blood - chemiluminescence - electrical currents - electrical organs - flying - noises - olfactory organ - skin - heart - gills - lateral line - luminous bacteria - Lorenzini - magnetism - maneuverability - pain - tail fin - swim bladder - lateral line organ - Temperature - tongues
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