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What is a lateral line in fish? The functions and diseases of the lateral line.
By Carl Strohmeyer Updated 5/9/14
The Lateral Line in Fish as well as Lateral Line Disease or Head and Lateral Line Erosion (HLLE)
The lateral line is a sense organ that consists of a row of scales that most fish have along their sides, extending from their head to tail. Under these scales are a system of fluid-filled canals and specialized cells which transmit vibrations to the brain of the fish.
The lateral line helps fish to detect movement and vibration in the surrounding water including predators and prey. The lateral line or similar organs in fish such as blind cavefish (which has rows of neuromasts on their heads) are used precisely to locate food without the use of sight.
Killifish can sense ripples caused by insects struggling on the surface of the water.
Scientific experiments with Pollack Fish have shown that the lateral line is also used for schooling behavior.
Lateral lines are usually visible as faint lines running lengthwise down each side, from the area around the gill covers to the area near the base of the tail. Sometimes parts of the lateral line are modified into electro-receptors (biological ability to receive and make use of electrical impulses), which are organs used to detect electrical impulses.
A Scientist in the 1960s named Sven Dijkgraaf argued convincingly that fish must use their lateral lines to detect water motion. This motion can be generated by the fish, water currents, or by some external moving object.
The lateral line in fish seems to have the ability of detecting the subtle movements of biological sources (prey fish or predator fish, for example) located some distance away. Many scientists believe that fish such as sharks can use these organs to detect magnetic fields as well.
HOW THE LATERAL LINE WORKS:
There are receptors in the line, called neuromasts, each consist of a group of hair cells, these cell hairs are surrounded by a protruding cupula (an organ that gives an animal a sense of balance).
Neuromasts may occur singly, in small groups called pit organs, or in rows within grooves or canals, where by these neuromasts are referred to as the lateral line system.
The lateral line system runs along the sides of the body onto the head, where it divides into three branches, two to the snout and one to the lower jaw.
These neuromasts are usually at the bottom of a pit or groove in the fish, which is large enough to be visible.
Skates, rays and sharks usually have lateral-line canals, in which the neuromasts are not directly exposed to the environment, but communicate with it via canal pores.
The hair cells in the lateral line are similar to the hair cells inside the others vertebrates inner ear (such as the cupula in humans where hair cells within the cupula sense rotational acceleration), indicating that the lateral line and the inner ear share a common origin.
Some active fish that are constantly swimming tend to have more neuromasts in canals than on the surface, and the lateral line will be further away from pectoral fins, to reduce the noise generated by fin motion.
The lateral line system, found in many fish, is sensitive to differences in water pressure. These differences are thought to be due to changes in depth or to the current like waves caused by approaching objects.
When pressure waves cause the gelatinous caps of the neuromasts to move, bending the enclosed hairs, the frequency of the nerve impulses is either increased or decreased, depending on the direction of bending.
A swimming fish sets up a pressure wave in the water that is detectable by the lateral line systems of other fish. It also sets up a bow wave in front of itself, the pressure of which is higher than that of the wave flow along its sides.
These near-field differences are registered by its own lateral line system.
As the fish approach an object, such as a rock or the glass wall of an aquarium, the pressure waves around its body are distorted, and these changes are quickly detected by the lateral line system, enabling the fish to turn or to take other actions.
Because sound waves are waves of pressure, the lateral line system is also able to detect very low-frequency sounds of about 100 Hz or less.
An adaptation of the pressure-sensitive system is seen in the modified groups of neuromasts called the Ampullae of Lorenzini (special sensing organs, forming a network of jelly-filled canals), which are found in sharks, rays and a few bony fish.
The Ampullae of Lorenzini are able to detect electrical charges, or fields, in the water.
Most animals, including humans, emit a DC (Direct Current) field when in seawater. This is thought to be caused by electrical potential differences between body fluids and seawater and between different parts of the body. An AC field is also set up by muscular contractions.
A wound, even a scratch, can alter these electrical fields.
DISEASES OF THE LATERAL LINE:
Often the lateral line in fish, marine in particular will get infections or degenerate from water conditions. Many believe Marine Head and Lateral Line Erosion is related to Hole in the Head (HITH).
The usual progression in marine fish of MHLLE (Marine Head and Lateral Line Erosion) is usually the development of small pits around the eye and on the head and adjacent area.
As the ailment progresses, the holes grow larger, eventually connecting to become larger lesions, eventually extending back along the fish's lateral line. The fins and gill covering will also often erode in more advanced cases, although MHLLE is seldom fatal.
Yellow Tangs for an unknown reason progress differently; they tend to lose their vibrancy and lighten in overall color, followed fin erosion, usually beginning with the soft tissue between the dorsal fin's rays.
In general Marine Angels and Tangs (Surgeonfish) seem to be the most susceptible to MHLLE.
Vitamin, immune system
Vitamin and mineral deficiencies such as Vitamin C and possibly Vitamin B complex are one very likely cause of degeneration from my experience.
Proper feeding of foods high in these vitamins such as Spirulina Algae will help in this case.
These deficiencies along with poor water quality (which often results in poor Redox balance) show the most evidence for being the major cause of this affliction.
More information about: Aquarium Redox
A Resource for: Spirulina Algae Fish Food Flake
Many have attributed high nitrates due to poor water quality as a possible cause, however although low nitrates are certainly important for long term health, I believe high nitrates play a minor role in how poor water affects HLLE in fish.
I believe from my own tests (as well as research) that the lack of minerals and vitamins in low quality water along with a poor Redox Potential are the main culprits. I have witnessed Yellow Tangs turn around with the addition of trace elements in client’s tanks that previously never supplemented them.
As stated earlier the use of products such as Spirulina Algae, high quality additives such as SeaChem Vitality (as a fish food soak), adding trace elements & complete buffers as well a simple and basic water changes using quality salts aids profoundly in maintaining proper mineral/vitamin levels in marine fish. This is especially important since marine fish constantly drink the water around them which makes their body chemistry very much like that of the water around them (somewhat of an over simplification though).
Also for finicky marine fish such as many Butterflies and Angels, the use of products that entice the fish to eat high quality prepared fish food that they might otherwise ignore is suggested; one excellent example is SeaChem Entice
A Great Resource for more about Marine Fish & how they drink water:
Aquarium Answers, Do fish drink water?
Another aspect of water quality, immune system health is the The Aquarium Redox Potential.
Without going into a long explanation, simply put a correct Redox potential acts as an anti-oxidant clearing away free radicals much the way many vitamins such as A, C and others do. Many aquarists are unfortunately unaware of this aspect of the aquarium keeping even though many human studies have shown direct correlation to correct Redox and lowering of free radicals.
PLEASE reference this article for more on this subject:
“The Aquarium Redox Potential”.
UV Sterilizer use for Redox Balance
STRAY ELECTRICAL CURRENT
Another theory is that an un-grounded aquarium can cause electrical fields that both interfere and degenerate the lateral line in fish. You can test this by using a pocket multi-meter on AC volts with a probe in the wall ground and a probe in the water.
HOWEVER, newer evidence does not seem to support this theory which quite bluntly from my experience makes sense as I have witnessed many broken or leaking electrical devices over years that I can actually feel the “stray” electrical current by holding my hand just above the water or if I have an open cut, YET the fish do not seem to be affected UNTIL one completes the circuit. An example is a Pacu I witnessed that “bit” into a loose set of wires that a client had left hanging into the tank, all was fine until the fish “completed” the circuit.
My point is that there is NO completed circuit until you complete it with a ground, which you do when touching the water while standing on the ground.
For further information, please see this article: Stray Voltages Explained
Other HLLE theories include the use of activated carbon, however in admittedly non-controlled studies I have seen no difference in occurrence or cure with the use of carbon, however it is possible that many are not keeping up with trace elements, and have a poor Redox and then the addition of carbon might remove what little anti-oxidants there are in an aquarium, but I do not think one can safely state that the use of carbon will lead to HLLE.
Exposure to Copper is another theory, however once again since I used to use copper extensively many years back I never observed any such correlation.
Viruses, bacteria and parasites have also been blamed and once again I have not seen enough supporting evidence to support this theory as well.
Finally two more theories that do make sense (although not scientifically proven) are lack of sunlight or correct lighting.
Proper lighting (or lack thereof) is another parameter for a healthy lateral line in fish.
Full spectrum lighting such as a combination 6,400 K or 20,000 K bulb and Actinic (UVA) bulb will help with this. The thought is that full spectrum lighting aids in the assimilation of certain vitamins, much as in humans and Vitamin D.
Please reference this very in depth article:
Proper Aquarium Lighting
* The Krib- Lateral Line Disease
*Hypothesis of Head and Lateral Line Erosion in Fish, Part 1
* Hypothesis of Head and Lateral Line Erosion in Fish, Part 2
*Hypothesis of Head and Lateral Line Erosion in Fish, Part 3
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