A More Technical Discussion of Fish Stress
Intro
I don’t prefer to write in technical or scientific terms. My personal belief is that, anything (like terminology) that separates the aquarist from useful information is of little value in this hobby. For that reason (and others) I write (hopefully) in a way to make the message both meaningful and easy to understand. That was the foundation of this post: Fish Stress – General, where I could provide some practical, non-technical information to the hobbyist. My emphasis in this post will be the physiological (technical) effects of stress on marine fishes.
What I don’t want to imply by not being technical in the above referenced post, is that fish stress is a huge mystery. Fish stress has a technical aspect and much sophisticated information on fish stress has been gathered through study, tests, research, and data collection. I’d like to make the reader aware of some of the results of those efforts.
Stress is a continuous, ongoing part of a fish’s life. Thus, stress reduction is approached the same way by the marine aquarist. The efforts to reduce and eliminate stress is continuous and ongoing. If the marine aquarist stops in this duty, things go wrong in the aquarium and with the marine life. Diligence in stress reduction is required to be successful in this hobby.
I didn't make this a sticky, since it may be of minimal value to most hobbyists. But, if there is a curiosity about this subject, this post may serve to whet the appetite.
As usual, this information comes to the hobby through work performed with and on food fishes. Most of that work is done on freshwater fishes. Some have been done on marine food fishes, but not much. How much of this information applies to ornamental reef fishes is debatable, but I believe, in general, there is some degree of applicability, even if it isn’t 100%. So, let’s get going!
Definition
This is one area I like simplicity, but the high-tech people obtaining research monies have to appear more scientific. So in more technical terms, fish stress is:
A factor or situation which induces physiological changes, which can impact energy use, osmoregulation, respiration, and immunity, including situations which fall outside the fish’s normal realm of tolerance.
That’s a mouthful. In my semi-meaningful yet simplistic terminology, stress is anything that causes the fish to be uncomfortable. Breaking down the technical definition above may go something like this: “. . .induces physiological changes. . .†= changes the internal chemical functions and/or internal chemistry of the fish. “. . .outside the fish’s normal realm of tolerance. . .†= something the fish doesn’t usually have to contend with (in the wild). The list of stressor sources is extensive and are covered in the other post: Fish Stress – General.
Stress Effects
The definition sort of says what can be the expected results of stress. But in more precise terms, some results of stress on a fish include:
no visual signs
abnormal behavior
increase in breathing
increase in blood pressure
decrease in immune response
increased susceptibility to disease
decreased reproductive performance, and
death
Abnormal behavior is elusive, unless the aquarist has extensive experience with that species of fish in captivity.
Increase in breathing is caused by dozens of different reasons, so that doesn’t help much. Noteworthy is that 'normal' breathing rate is below 90 ‘swallows’ per minute.
It’s of no surprise that the marine aquarist won’t be taking their fish’s blood pressure.
There is a good amount of scientific information regarding how stress causes a decrease in immune response.
The reader has to get it firmly into the brain that stress is not usually visible. The concept of, 'My fish is happy' is absurd. The fish cannot show stress all the time and cannot show when there is no stress. We can only determine stress from the effects it has on the fish, and then only when things go wrong or when their life is cut short. Marine aquarists need to avoid falling into the pit of putting human emotions onto their fish's behavior. They don't fit.
If the reader can imagine stress in fish being similar to people with diabetes, it might become more clear on what effects to expect. In a room full of people can the diabetics be identified? No. But if clinical test results were available and the normal and abnormal internal chemistries were known, there would be more information to determine the diabetics from those who aren't. In some respects, a fish suffering from stress may not have an outward appearance of its condition, but there are clinical/internal chemical (physiological) signals. Those physiological exhibits of stress include abnormal levels of:
catecholamines
cortisol
corticosteroids
glucose
If the reader has grasped the information so far, then it is an easy conclusion that, putting it all together into a bigger picture, the stressed fish has an increased susceptibility to disease. This includes a suppressed inflammatory response and not keeping up the mucous coating proteins.
Lastly, a stressed fish can exhibit decreased reproductive performance. This is not a visible signal to the marine aquarist, but through post mortem exams (necropsy) of internal organs, including reproductive organs, the qualified person can discern signs attributed to unknown stressors after disease is eliminated. The reproductive organs should have developed properly (timely) and when they don't it is often because the fish was the target of some stressor.
Physiological Changes
Things are getting more technical now and more to the point of this post. If you can’t follow along, don’t be discouraged.
I would like to ramble a bit here. You would think that a fish's body under stress would muster its defenses to help the fish in terms of defeating the stressor. After all, when humans are threatened by a pathogen our bodies rally by initiating the immune response and for injury, the inflammatory response. This isn’t the fact with marine ornamental fishes. Recent evidence has shown that when a fish goes into a ‘stress mode’ it reduces or totally shuts down its immune response; and tones down their inflammatory response! :shock: Just the opposite of what you’d think. This makes stressed fish particularly susceptible to disease and parasitic attack. Why does their body do this?
Simply, the fish has direct contact and depends upon its watery environment. Unlike humans, the fish is so connected with its immediate environment (water) that it is the target of anything wrong with that environment. When stressed, the fish first must devote energy and effort to resist the stressor. A chemical stressor example might be easier to understand:
If the stressor is chemical in nature (like bad water quality), the fish energy is routed to keeping the insides of the fish stable -- resisting the outside chemical change would cause. Other defenses are also scaled back, like mucous production and the inflammatory response.
A fish can actually adapt to some minor stressors for a short period of time. But this adaptation is not without a price. Such adaptation depletes energy reserves. In so doing the fish begins to divert energy from other uses (immunity, inflammatory response, reproductive organs, organ maintenance, mucous protein production, growth, etc.) to stabilizing itself internally. In these cases, the fish may appear to be normal to the aquarist, but the internal chemistry of the fish is 'falling apart.'
Still worth mentioning I think (and relevant to this section on Physiological Changes) is that stress needs to be considered by the aquarist as an ongoing thing. It is not like an injury which happens and now the fish has to heal. It’s a continuous and (can be) a very subtle thing.
I think most seasoned aquarists (which resist or don’t use a quarantine method) have observed that during a disease outbreak in their display, not all fish seem to be infected, or not all fish get infected to what appears to be the same degree or level. That is because each individual fish (not just the species) has differences that dictate its responses to pathogens (monerans (bacteria), protists (one-celled animals and plants), fungus, parasites and viruses). These differences are attributed to genetics, nutrition, handling, injury, care for that particular fish, etc. By “care†in the hobbyist sense, it would be like the fish obtaining different attention than other fishes in the same system. This is also like the fish pushing other fishes out of its way to get more than its share of food. (This last example is one where the community of fishes were not put together well by the aquarist).
Part of the above mentioned differentiation in which fish get infected or ill, is the physiological (internal chemical) response the fish makes to the stressor. Each fish has a varying degree of altered physiology which affects their ability to ward off disease and control a stressor(s).
Studies, Research, and Observations
One physiological response that has been studied in fish under stress, is that they release various hormones from the adrenal gland. These hormones decrease the fish’s ability to initiate or sustain an inflammatory response. That is to say that a stressed fish will release hormones that suppress the immune system. This leads to more susceptibility to a pathogen, since the inflammatory response is a key factor in the process to fight disease. [Francis-Floyd, R. CIR919, Fisheries and Aquatic Sciences Dept., FL Cooperative Extension Service, Inst. of Food and Agricultural Sciences, Univ of FL, July, 2002]
What exactly is a treatment? Most fish pathogen disease treatments are really and should be though of as this: A pathogen treatment weakens the pathogen enough so that the fish’s own defenses can overcome the pathogen.
The reader should be able to see then, how stress leads to reduced resistance to disease, and how continued stress can reduce the fish’s ability to recover from a disease. This is a reason to question stress before, during, and after disease treatments. If the stressors aren’t removed or significantly reduced, treatments may either not be effective, or the fish will return to its state of susceptibility to the pathogens. This could render a treatment semi-useless. You may see me post a response to a problem that includes recommendations to fix the water quality, or remove a particular stressor.
Another aspect of the hormone release and adrenal gland activity. . .Fish store simple carbohydrates (like sugars) for emergency use (like having a sudden need to put distance between them and a Barracuda!). The hormone released by the adrenal gland releases the stored carbohydrates to make them available to the stressed fish. If the stressor(s) are not reduced or eliminated, the fish comes to the end of its energy reserves, the energy diverted to addressing the stressor(s) (see above) is not enough, and the fish enters into a condition where it cannot fight off a (secondary) pathogen, nor to continue to adapt to the stressor(s). In short, things quickly fall apart.
In the absence of available energy (the stored carbohydrates) the fish stops growing. I guess this doesn’t seem like much unless the reader understands that throughout the entire life of a marine fish, the fish continues to grow. In our aquariums, the fish size may be stunted, but the fish continues to grow. If the fish is not obtaining needed nutrients, insufficient quantities of food, or under other stressors (like a poor environment), the fish stops growing. So aquarists who boast, “My fish never got above 5 inches in length†when the fish gets to 10" in size in captivity, are saying in effect, ‘My fish has been stressed, undernourished, and/or kept in a tank affording a poor environment, so my fish stopped growing.’ You can spot those who make these kinds of statements and now you know why their fish hasn’t grown to its proper size! Such statements are sometimes in defense of what they feed the fish or how often they feed the fish or sometimes, most discouraging, is a conscious effort to keep the fish small to suit its available space. All such fishes are surviving, not thriving. (See: Survive or Thrive?).
Osmoregulation is affected by stressors in the sense of how the fish will regulate mineral metabolism. Simply put (I hope) osmoregulation is the ability of a salt water fish to prevent it from dehydrating from water loss to its environment. Many organs are involved in this process. [Greenwell MG, Sherrill J, Clayton LA. 203. Osmoregulation in fish. Mechanisms and clinical implications. Vet Clin North Am Exot Admin Pract. 6(1):169-89]. When the fish is short on energy, the amount of energy for osmoregulation to continue properly increases making it harder for the fish to perform this vital function. It's a bit of a 'catch.' The less available the energy, the more energy is needed to do the same job.
One particularly interesting point should be mentioned (even though this section of the post could go on and on and on. . .). The effect of temperature changes. Humans don’t relate to the sensitivity a fish has to a temperature change (up or down). But it is known that a small temperature change has an impact on the fish’s ability to ward off a disease. Most seasoned aquarists (mostly those that resist or don’t us a quarantine process) may see a disease outbreak in their marine aquarium right after a ‘rapid’ temperature change. A fish needs time to acclimate to water chemistry and parameter changes. See: Fish Acclimation Procedure
In the case of temperature shifts, what happens (on a more technical level) is that the fish’s system doesn’t acclimate fast enough to the change. A temperature drop then turns into a stressor. As noted above. . .This produces in the fish a diverting of energy to handle the stressor (temp). The consequence is less energy to the immune response. Should there be any pathogens around, they now have the opportunity to take advantage of the now disadvantaged fish with the slow or crippled immune response. What follows is an 'outbreak' or 'bloom' of the pathogen(s).
The fish’s immune response is a mechanism for the fish to produce antibodies to invading pathogens. It is less sophisticated than human immunity AND the reader should understand the 'immunity' can be the proteins in the mucous layer that 'resist' (rather than destroy) the pathogen. If this response is slowed or compromised by a temperature shift (or any stressor, like a new fish introduced into the display) in the presence of pathogens that haven't gotten a good foothold, balance is shifted to the advantage of the pathogen. What the aquarist sees after the temperature shift is a disease outbreak in part due to this slowed response. [Francis-Floyd, R - same reference given above - ] The error made by the learning aquarist when the stressor is the new fish, is that 'the new fish brought in a disease.' It could simply be that the new fish was the stressor that put some fishes into a reduced immunity mode, which then shifted the balance to the advantage of the pathogen.
Prevention and Summary
I’ve left prevention in more practical terms to the Fish Stress – General post.
Like written in the Intro: Stress prevention/reduction is continuous. Like stress is ongoing and continuing, so must prevention be ongoing and continuous. The aquarist must always be vigilant to controlling stress (from the fish's point of view).
The reader sees from the above some of the more technical aspects of fish stress. I hope this provides a broader understanding of stressors from a fish physiological perspective. I tried to soften the technical aspects without getting bogged down in too many new words or phrases. Hopefully, this will be of some interest.
Intro
I don’t prefer to write in technical or scientific terms. My personal belief is that, anything (like terminology) that separates the aquarist from useful information is of little value in this hobby. For that reason (and others) I write (hopefully) in a way to make the message both meaningful and easy to understand. That was the foundation of this post: Fish Stress – General, where I could provide some practical, non-technical information to the hobbyist. My emphasis in this post will be the physiological (technical) effects of stress on marine fishes.
What I don’t want to imply by not being technical in the above referenced post, is that fish stress is a huge mystery. Fish stress has a technical aspect and much sophisticated information on fish stress has been gathered through study, tests, research, and data collection. I’d like to make the reader aware of some of the results of those efforts.
Stress is a continuous, ongoing part of a fish’s life. Thus, stress reduction is approached the same way by the marine aquarist. The efforts to reduce and eliminate stress is continuous and ongoing. If the marine aquarist stops in this duty, things go wrong in the aquarium and with the marine life. Diligence in stress reduction is required to be successful in this hobby.
I didn't make this a sticky, since it may be of minimal value to most hobbyists. But, if there is a curiosity about this subject, this post may serve to whet the appetite.
As usual, this information comes to the hobby through work performed with and on food fishes. Most of that work is done on freshwater fishes. Some have been done on marine food fishes, but not much. How much of this information applies to ornamental reef fishes is debatable, but I believe, in general, there is some degree of applicability, even if it isn’t 100%. So, let’s get going!
Definition
This is one area I like simplicity, but the high-tech people obtaining research monies have to appear more scientific. So in more technical terms, fish stress is:
A factor or situation which induces physiological changes, which can impact energy use, osmoregulation, respiration, and immunity, including situations which fall outside the fish’s normal realm of tolerance.
That’s a mouthful. In my semi-meaningful yet simplistic terminology, stress is anything that causes the fish to be uncomfortable. Breaking down the technical definition above may go something like this: “. . .induces physiological changes. . .†= changes the internal chemical functions and/or internal chemistry of the fish. “. . .outside the fish’s normal realm of tolerance. . .†= something the fish doesn’t usually have to contend with (in the wild). The list of stressor sources is extensive and are covered in the other post: Fish Stress – General.
Stress Effects
The definition sort of says what can be the expected results of stress. But in more precise terms, some results of stress on a fish include:
no visual signs
abnormal behavior
increase in breathing
increase in blood pressure
decrease in immune response
increased susceptibility to disease
decreased reproductive performance, and
death
Abnormal behavior is elusive, unless the aquarist has extensive experience with that species of fish in captivity.
Increase in breathing is caused by dozens of different reasons, so that doesn’t help much. Noteworthy is that 'normal' breathing rate is below 90 ‘swallows’ per minute.
It’s of no surprise that the marine aquarist won’t be taking their fish’s blood pressure.
There is a good amount of scientific information regarding how stress causes a decrease in immune response.
The reader has to get it firmly into the brain that stress is not usually visible. The concept of, 'My fish is happy' is absurd. The fish cannot show stress all the time and cannot show when there is no stress. We can only determine stress from the effects it has on the fish, and then only when things go wrong or when their life is cut short. Marine aquarists need to avoid falling into the pit of putting human emotions onto their fish's behavior. They don't fit.
If the reader can imagine stress in fish being similar to people with diabetes, it might become more clear on what effects to expect. In a room full of people can the diabetics be identified? No. But if clinical test results were available and the normal and abnormal internal chemistries were known, there would be more information to determine the diabetics from those who aren't. In some respects, a fish suffering from stress may not have an outward appearance of its condition, but there are clinical/internal chemical (physiological) signals. Those physiological exhibits of stress include abnormal levels of:
catecholamines
cortisol
corticosteroids
glucose
If the reader has grasped the information so far, then it is an easy conclusion that, putting it all together into a bigger picture, the stressed fish has an increased susceptibility to disease. This includes a suppressed inflammatory response and not keeping up the mucous coating proteins.
Lastly, a stressed fish can exhibit decreased reproductive performance. This is not a visible signal to the marine aquarist, but through post mortem exams (necropsy) of internal organs, including reproductive organs, the qualified person can discern signs attributed to unknown stressors after disease is eliminated. The reproductive organs should have developed properly (timely) and when they don't it is often because the fish was the target of some stressor.
Physiological Changes
Things are getting more technical now and more to the point of this post. If you can’t follow along, don’t be discouraged.
I would like to ramble a bit here. You would think that a fish's body under stress would muster its defenses to help the fish in terms of defeating the stressor. After all, when humans are threatened by a pathogen our bodies rally by initiating the immune response and for injury, the inflammatory response. This isn’t the fact with marine ornamental fishes. Recent evidence has shown that when a fish goes into a ‘stress mode’ it reduces or totally shuts down its immune response; and tones down their inflammatory response! :shock: Just the opposite of what you’d think. This makes stressed fish particularly susceptible to disease and parasitic attack. Why does their body do this?
Simply, the fish has direct contact and depends upon its watery environment. Unlike humans, the fish is so connected with its immediate environment (water) that it is the target of anything wrong with that environment. When stressed, the fish first must devote energy and effort to resist the stressor. A chemical stressor example might be easier to understand:
If the stressor is chemical in nature (like bad water quality), the fish energy is routed to keeping the insides of the fish stable -- resisting the outside chemical change would cause. Other defenses are also scaled back, like mucous production and the inflammatory response.
A fish can actually adapt to some minor stressors for a short period of time. But this adaptation is not without a price. Such adaptation depletes energy reserves. In so doing the fish begins to divert energy from other uses (immunity, inflammatory response, reproductive organs, organ maintenance, mucous protein production, growth, etc.) to stabilizing itself internally. In these cases, the fish may appear to be normal to the aquarist, but the internal chemistry of the fish is 'falling apart.'
Still worth mentioning I think (and relevant to this section on Physiological Changes) is that stress needs to be considered by the aquarist as an ongoing thing. It is not like an injury which happens and now the fish has to heal. It’s a continuous and (can be) a very subtle thing.
I think most seasoned aquarists (which resist or don’t use a quarantine method) have observed that during a disease outbreak in their display, not all fish seem to be infected, or not all fish get infected to what appears to be the same degree or level. That is because each individual fish (not just the species) has differences that dictate its responses to pathogens (monerans (bacteria), protists (one-celled animals and plants), fungus, parasites and viruses). These differences are attributed to genetics, nutrition, handling, injury, care for that particular fish, etc. By “care†in the hobbyist sense, it would be like the fish obtaining different attention than other fishes in the same system. This is also like the fish pushing other fishes out of its way to get more than its share of food. (This last example is one where the community of fishes were not put together well by the aquarist).
Part of the above mentioned differentiation in which fish get infected or ill, is the physiological (internal chemical) response the fish makes to the stressor. Each fish has a varying degree of altered physiology which affects their ability to ward off disease and control a stressor(s).
Studies, Research, and Observations
One physiological response that has been studied in fish under stress, is that they release various hormones from the adrenal gland. These hormones decrease the fish’s ability to initiate or sustain an inflammatory response. That is to say that a stressed fish will release hormones that suppress the immune system. This leads to more susceptibility to a pathogen, since the inflammatory response is a key factor in the process to fight disease. [Francis-Floyd, R. CIR919, Fisheries and Aquatic Sciences Dept., FL Cooperative Extension Service, Inst. of Food and Agricultural Sciences, Univ of FL, July, 2002]
What exactly is a treatment? Most fish pathogen disease treatments are really and should be though of as this: A pathogen treatment weakens the pathogen enough so that the fish’s own defenses can overcome the pathogen.
The reader should be able to see then, how stress leads to reduced resistance to disease, and how continued stress can reduce the fish’s ability to recover from a disease. This is a reason to question stress before, during, and after disease treatments. If the stressors aren’t removed or significantly reduced, treatments may either not be effective, or the fish will return to its state of susceptibility to the pathogens. This could render a treatment semi-useless. You may see me post a response to a problem that includes recommendations to fix the water quality, or remove a particular stressor.
Another aspect of the hormone release and adrenal gland activity. . .Fish store simple carbohydrates (like sugars) for emergency use (like having a sudden need to put distance between them and a Barracuda!). The hormone released by the adrenal gland releases the stored carbohydrates to make them available to the stressed fish. If the stressor(s) are not reduced or eliminated, the fish comes to the end of its energy reserves, the energy diverted to addressing the stressor(s) (see above) is not enough, and the fish enters into a condition where it cannot fight off a (secondary) pathogen, nor to continue to adapt to the stressor(s). In short, things quickly fall apart.
In the absence of available energy (the stored carbohydrates) the fish stops growing. I guess this doesn’t seem like much unless the reader understands that throughout the entire life of a marine fish, the fish continues to grow. In our aquariums, the fish size may be stunted, but the fish continues to grow. If the fish is not obtaining needed nutrients, insufficient quantities of food, or under other stressors (like a poor environment), the fish stops growing. So aquarists who boast, “My fish never got above 5 inches in length†when the fish gets to 10" in size in captivity, are saying in effect, ‘My fish has been stressed, undernourished, and/or kept in a tank affording a poor environment, so my fish stopped growing.’ You can spot those who make these kinds of statements and now you know why their fish hasn’t grown to its proper size! Such statements are sometimes in defense of what they feed the fish or how often they feed the fish or sometimes, most discouraging, is a conscious effort to keep the fish small to suit its available space. All such fishes are surviving, not thriving. (See: Survive or Thrive?).
Osmoregulation is affected by stressors in the sense of how the fish will regulate mineral metabolism. Simply put (I hope) osmoregulation is the ability of a salt water fish to prevent it from dehydrating from water loss to its environment. Many organs are involved in this process. [Greenwell MG, Sherrill J, Clayton LA. 203. Osmoregulation in fish. Mechanisms and clinical implications. Vet Clin North Am Exot Admin Pract. 6(1):169-89]. When the fish is short on energy, the amount of energy for osmoregulation to continue properly increases making it harder for the fish to perform this vital function. It's a bit of a 'catch.' The less available the energy, the more energy is needed to do the same job.
One particularly interesting point should be mentioned (even though this section of the post could go on and on and on. . .). The effect of temperature changes. Humans don’t relate to the sensitivity a fish has to a temperature change (up or down). But it is known that a small temperature change has an impact on the fish’s ability to ward off a disease. Most seasoned aquarists (mostly those that resist or don’t us a quarantine process) may see a disease outbreak in their marine aquarium right after a ‘rapid’ temperature change. A fish needs time to acclimate to water chemistry and parameter changes. See: Fish Acclimation Procedure
In the case of temperature shifts, what happens (on a more technical level) is that the fish’s system doesn’t acclimate fast enough to the change. A temperature drop then turns into a stressor. As noted above. . .This produces in the fish a diverting of energy to handle the stressor (temp). The consequence is less energy to the immune response. Should there be any pathogens around, they now have the opportunity to take advantage of the now disadvantaged fish with the slow or crippled immune response. What follows is an 'outbreak' or 'bloom' of the pathogen(s).
The fish’s immune response is a mechanism for the fish to produce antibodies to invading pathogens. It is less sophisticated than human immunity AND the reader should understand the 'immunity' can be the proteins in the mucous layer that 'resist' (rather than destroy) the pathogen. If this response is slowed or compromised by a temperature shift (or any stressor, like a new fish introduced into the display) in the presence of pathogens that haven't gotten a good foothold, balance is shifted to the advantage of the pathogen. What the aquarist sees after the temperature shift is a disease outbreak in part due to this slowed response. [Francis-Floyd, R - same reference given above - ] The error made by the learning aquarist when the stressor is the new fish, is that 'the new fish brought in a disease.' It could simply be that the new fish was the stressor that put some fishes into a reduced immunity mode, which then shifted the balance to the advantage of the pathogen.
Prevention and Summary
I’ve left prevention in more practical terms to the Fish Stress – General post.
Like written in the Intro: Stress prevention/reduction is continuous. Like stress is ongoing and continuing, so must prevention be ongoing and continuous. The aquarist must always be vigilant to controlling stress (from the fish's point of view).
The reader sees from the above some of the more technical aspects of fish stress. I hope this provides a broader understanding of stressors from a fish physiological perspective. I tried to soften the technical aspects without getting bogged down in too many new words or phrases. Hopefully, this will be of some interest.
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