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Thread: Fish Stress - General

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    Brittle Starfish

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    May 2006
    So CA
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    Fish Stress - General


    We all want our fish to thrive rather than just survive (see: Thrive or Survive?). The difference is usually based upon the pressure put upon the fish through encounters from captivity to its home in the marine system display tank.

    Stress is just a link in a chain of conditions. Generally first comes discomfort. Next comes stress. Last is pain.

    Stress is one of the most often used words when it comes to any general health and care discussion of the ornamental marine fish in our aquariums. When we speak of it, we include the concept of 'discomfort' along with stress, though the two in more technical areas, are kept separate. Although rarely recognised it is in fact the cause for most marine fish ailments, diseases, conditions, and deaths. Describing and working with something you can’t see or properly diagnose is a challenge. It is the root of most health problems of marine ornamental fishes. Stress is blamed so often that it may seem to the novice that stress is some kind of joke amongst seasoned aquarist. Sort of like the doctor that can’t figure out what’s wrong with the patient so the doctor says, “It must be a virus.”

    But ornamental fish husbandry has come a long way in understanding stress. It's not just an answer to what we aren't sure has happened, or a reason for an unexpected death. Stress in fact is much better understood today than 30 years ago. Using this information and experience is the key to a long lived and healthy captive fish. Can stress be eliminated? We'll see.

    I've divided this 'article-post' into 7 parts. Intro (this part), Definition, Appearance, Sources, Reducing Stress, Outcomes, Summary, and References.
    What is it?
    It is literally anything (real or imagined by the fish) that causes the fish to be uncomfortable.
    What does stress in a fish look like?
    When a fish is under stress there is always one sure visible sign – nothing! When a fish is under stress there are always blood indicators. Test the blood of the fish and you will know if the fish is under stress. This is the technical side of stress and more information can be found here: Fish Stress – A Technical/Physiological Approach.

    There may be visual hints or clues such as a fish that shows its night-time colors/patterns during the day-time are indicating they are under stress. Signs range from the appearance of 'everything is fine' to tattered fins and a vacant expression. Stress can manifest itself in fish behavior. For instance, a fish that is doing something repetitive (like 'pacing' back and forth in the tank, or constantly picking at the same 'thing' in the tank where there is obviously no food) can be showing signs of stress. Sometimes a chronic (long term stress) shows itself by the fish 'wasting.' The fish thins to death. Quite often it is a fish that has stopped eating, sending a signal to the aquarist that there is stress. The thing about stress is that it can come at the fish being chronic (a slow effect) or acute (a very fast effect). It is the slow effects of stress that are usually ignored or left unnoticed by aquarists. Just remember: just because stress isn't obvious, doesn't mean it isn't there and happening.

    Probably the best human analogy to what stress in a fish looks like would be people with diabetes. In a room mixed of people with and without diabetes, can you visually pick out the ones with diabetes? However, do blood tests, urine tests and monitor the person, and the diabetics are found. Same with the fish. Stress can be measured in the fish’s blood. (See: Fish Stress – A Technical/Physiological Approach).
    Where does stress come from?
    Anywhere. Some sources are more obvious than others. Stress is generated by any and all of the following and more:
    a) capture
    b) transportation
    c) mental
    d) fear/security
    e) acclimation
    f) space
    g) tank mates
    h) water quality (water changes, crowding, poor maintenance, etc.)
    I) lighting
    j) disease, illness, health issues
    k) treatments and medicines
    l) nutritional deficiency
    What can we do about relieving stress?
    From the above mentioned sources of stress, it is obvious some of the things that can be done and not done to reduce stress on the fishes. Some things are in the aquarist’s control, others aren’t. I will address each one of the identified sources as to how to go about reducing or eliminating that particular stressor.

    a) capture - is pretty much out of the aquarist’s control. But the aquarist should use the greatest power they have over the system – their money! Only buy fish that are absolutely healthy. Don’t be a ‘saviour’ and setup a fish hospital. All the hospital aquarist does is send the message back through the system that even poorly handled fish are saleable or salvageable. The marine aquarist is neither veterinarian nor a fish hospital. Follow these guidelines when acquiring a new fish: Should I buy that fish?.

    b) transportation - whether from the LFS to your home or if you choose to purchase fish on-line and have it delivered, the same applies to the aquarist as it does the exporter, wholesaler, and LFS. The least stressful trip is one where the temperature is held constant; the light remains constant (preferably dark or at least not in direct sunlight); the water is least polluted during the trip; and the container has not only enough water, but enough air/oxygen above the water. The best ratio I have found is that for every one part of water in the bag, there should be two parts of air/oxygen if the fish will be in the bag for more than 4 hours. Otherwise, 50/50 is good. The aquarist can’t usually tell the source how to ship if they are on the Internet, but again, the aquarist should use their power – money. The Internet shipper is usually only concerned about getting the bag(s) into a single box.

    c) mental - is pretty much the most difficult for the aquarist to control. If the fish is ‘mental’ what can you do? The best the aquarist can do is make the fish as comfortable as possible and hope they ‘come out of it.’ This means providing the hiding spaces and security that particular fish is used to having. Using a quarantine process helps these fish out tremendously. In fact the use of a quarantine process can reduce a lot of the stresses on this list. Use: A Quarantine Procedure.

    d) fear/security - is best addressed by providing hiding spaces (in the QT and aquascaping in the display tank). Controlling other stress factors (e.g., lighting) can improve the fish’s sense of security. People moving around the tank is another source of fear. Sometimes the aquarist forgets the size difference between their fish and humans. If you turned around and saw King Kong standing in front of you staring at you how would that make you feel? Have to clean out your shorts? Well, it is no less a shock for the new fish who has found, in general, association with these huge creatures (humans) to be painful and very stressful up to this point.

    e) acclimation - is a key point of the fish’s captive existence. Unfortunately the aquarist is at the end of a long line of acclimation attempts on the fish. The aquarist has control only on the last acclimation. I found, after 35 years of experimenting that this is the best acclimation process to the marine aquarist: Fish Acclimation Procedure. Follow this procedure closely and this stress put on the fish will be minimal – almost negligible.

    f) space - the final frontier? The stress of a fish not having enough space goes unnoticed for the most part. Some fish send vague signals that they are short on space (pacing and, aggressive behavior), or sometimes the fish will spend a lot of time facing into a powerhead to have the water flowing over them while they swim 'into the current,' others do nothing. The best the aquarist can do is not put fish in aquariums that are unsuitable to them. Tangs do belong in long aquariums (6 or more feet) when they are of almost any size. Large Angelfish transitioning to their adult pattern or which have already achieved their adult pattern, must be in aquariums no less than 180 gallons. Paired fish need more space than each would if they were single, so the aquarist must account for this added space. Some fish take tank bottom space (Gobies) so the allocation of bottom area is what is important to them, not the number of gallons in the aquarium. Fish swim horizontally, not up or down, so the height of the aquarium isn’t as important as its length and width. If you want to keep tangs and rabbitfishes (or any fish that travels a lot in the open ocean or seas), put them in long aquariums. Don't put fish like this in small aquariums, even if the fish is small now, thinking it will be okay for now. They are not okay. Baby fish that become large, long distant swimmers, need most of their full space right now.

    This is the hardest thing to convince the new aquarist who wants to own ‘everything.’ The aquarist sees Anemeonefishes in nano tanks and thinks it is okay. The new aquarist doesn’t ‘get the math.’ In more than 35 years in this hobby I can say from anecdotal evidence that fish put into small spaces die sooner. The oldest fish I know is a Tomato Anemonefish that has lived over 18 years in a 180 gallon aquarium (or larger). Yet I’ve known these same fish to die within a couple of years in a 29 gallon aquarium and, after a post mortem, show no signs of disease or malnutrition.

    Get on the Internet and take the advice of advanced, educated, and extensively experienced marine aquarists. Use some common sense. If a book lists 6 fishes all that are needing a 30 gallon aquarium minimum and the fishes are listed as getting up to 12" in captivity, is that 30 gallon going to hold all those fishes at that size? Most authors never kept those fishes they are giving advice about. Most Internet online sources just want to sell fish. Where did they get their advice from? When an online vendor sells the fish in three sizes (for instance) and lists a minimum of 30 gallons for that fish, what size of fish are they talking about? How many of those fish will fit in that sized space? An LFS knows usually less than the average aquarist when it comes to stocking limits. In effect, the LFS wants to sell fish and when they get ill, the LFS sells medication and/or more equipment. When you ask your LFS about whether or not a fish they are offering for sale will ‘fit’ into your display tank, remember that $40 fish cost the LFS about $2 to $4. Ask yourself, is that LFS going to stop you from buying that fish? Greed is a big motivator on the quality of advice the marine aquarist will get from retailers.

    g) tank mates - is not just a matter of planning. Planning is important, but fishes differ even within species. When a particular fish is not working out, the aquarist must recognise this and separate the fishes. This one (you'd think) is easy for the aquarist to control. It is best to have a plan of what you want in the aquarium and try to stick to it until evidence to the contrary shows up. If the compatibility of fishes on your wish list are unknown, get to a forum or friends and start asking around. I would definitely NOT recommend taking the advice of your LFS on this. Not that they are all wrong, don’t know, or lie (most do one or the other(s) in my experience) it’s just that they have a limited experience based upon crowded store tanks that don't reflect your community tank. There are stressors like the introduction of any new thing (decoration or marine life) to the aquarium. If the fish doesn’t like it or get used to it in a few days, it’s time to take one or the other or both out. Remember, when two fish don’t get along they are both under stress – the one chasing and the one being chased. Another subtlety is watching your community fishes during feeding time. Are any afraid to come to the feeding area? There are subtle signs of stress between fishes that often come out during feeding time. Watch closely and remove the aggressor or the recluse or both.

    h) water quality - can be a major stressor for fish and direclty under the control of the marine aquarist. The current emphasis in this hobby is to provide excellent water quality for corals and invertebrates, but fish benefit immensely from this, even if they are the ‘tougher fish.’ The fish drinks water and separates out the salt so that it can ‘take a drink’ of freshwater. The fish maintains its internal salt content through a process referred to as osmoregulation. This takes energy and if there is anything amiss with the water, then stress is added to the fish. Everything: temperature, salinity, ammonia, nitrites, pH, organics, etc. has a varying degree of impact on the fish depending upon not only what that species can tolerate, but what that one particular fish can tolerate.

    The aquarist thinks water quality is under control when the tests are performed and come out well. But there is much more to water quality than the test kits reveal. Please read: What is Water Quality

    One of the most overlooked water quality issue is the pH. Focus by the reefkeepers is to strictly control pH, for their invertebrates and corals, but pH is just as important to marine fishes as it is to the invertebrates and corals. Not all fish like the same pH. Tangs especially like a pH of 8.4. Many angelfishes like 8.3 to 8.4 pH. Large adult Angelfish in particular are found by new aquarists difficult to keep alive for more than a year. Some reasons why large adult Angelfishes are so challenging include space stressors (see above) and one of the other is pH and water quality control. Large adult Angelfishes need the best water and a steady pH in their preferred zone to live long and healthy lives. Large adult angelfish I've maintained have lived over 11 years in captivity and still going. As long as I've seen them live, I've seen them 'check out' quickly in tanks that aren't mature, water quality isn't maintain, or pH fluctuates.

    The best control the aquarist has in this area is to know what water quality issues are significant to that particular fish and then to keep track and control those issues! The next thing the aquarist should know about water quality is not to put fish into their marine system until that system has matured.

    A water change can be so stressful for a fish that it will die. Water changes have to be performed in a stress-free manner. See: How to Make a Successful Water Change.

    I) lighting - like for corals and invertebrates, is a matter of choosing the right ones suitable for the fish. Since the fish’s survival isn’t strongly linked to light, it's easy to choose the wrong bulb (a bulb high in UV content) for a fish. If the fish was collected from deep waters, then the fish isn’t used to bright lights. The fish must be given places to hide in the near dark, shade or holes, or not put into such an aquarium. Aquascaping to provide overhangs, holes, shade, and dark places will be important features for fishes coming from deeper water. Even fishes that supposedly come to us from the ‘coral reefs’ may in fact have been collected from deeper waters. So unexpectedly to the aquarist, the fish they have a darkness need and shade from the lights, but their friend’s same species of fish is fine being in the bright light. Watch for subtle signals of the fish avoiding well lit areas, and adjust the light intensity, composition, and aquascaping accordingly.

    j) disease, illness, health issues - are all sources of stress. The best the aquarist can do is first only buy quality fishes they think are healthy. Follow this advice closely: Should I buy that fish?. The next best step is using a quarantine process on all acquired marine life. It may sound stupid but, the only thing you want to get into the aquarium is the marine life you want, not the pathogens, hitchhikers, and undwanted life. Each fish should be kept in quarantine. Don’t take refuge in one liners like, “The fish looked healthy at the store.” Forget the dodge. Do the quarantine. Quarantine provides other reduced stress environments too (see above).

    k) treatments and medicines - is something directly under the control of the aquarists. Even though a treatment may be necessary for a sick fish, it still must be controlled and directions followed closely. If the aquarist has a choice between a hyposalinity treatment or using a copper medication (as in the case of Marine Ich (Cryptocaryon irritans)) then the hyposalinity treatment is easier on the fish. Some interesting info on copper stress can be found here: Copper Medications - Good, Bad, and Ugly. A fish stressed by a treatment or medicine may signal that stress by refusing to eat.

    l) nutritional deficiency - is something that is under the direct control of the aquarist! Aquarists don’t realize that they must provide their fishes with vitamins, fats, and trace elements besides the foods they usually feed. It is my opinion that no single prepared food contains everything, every fish needs, in the proper quantity and in a complete formula. Follow the guidelines here: Fish Health Through Proper Nutrition.
    What are the affects of stress on fish?
    Test the blood of the fish and you will know if the fish is under stress. This is the technical side of stress and that information can be found here: Fish Stress – A Technical/Physiological Approach.

    All the marine aquarist has is eyes and test kits. Probably the most outstanding of all final outcome is a shortened and less healthy life. This is hard for the aquarist to appreciate and accept. Aquarists often think their fish is fine. How many times do I hear that, ‘My fish is happy.’ Stress is not seen! That Tang ‘scooting merrily’ about the tank is finding too little space and is ‘scooting around’ because it is aggitated from the lack of space – NOT because it is HAPPY.

    Many marine fishes should live a long time in captivity. When they die in a year or even 5 years, the aquarist wonders why? Stressor(s) got to the fish. A stress the aquarist refused to acknowledge (most often something like needing more space, and/or not getting the right nutrition) or a stress the aquarist didn’t see/watch (water quality drifting from reduced maintenance over time).

    One outcome of stress is the fish succumbing to diseases and infections (mostly bacterial in nature) whereas an unstressed fish would be okay. This has to do with the shifts in physiology when a fish is stressed. (More on this here: Fish Stress – A Technical/Physiological Approach). Quite often, there is one fish in the tank affected, and not all the fish. The aquarist comes to the wrong conclusion, that nothing's wrong with the water, environment, tank-mates, etc. The aquarist thinks everything is fine when slowly one or more fish shows up with a cloudy eye, then two cloudy eyes on one fish, or develops Popeye, or has tattered fins when no other fish has been bothering it. The decline of the fish, either slowly or suddenly is the product of stress.

    The definitive outcome of stress is an untimely death. Misunderstood and often going unacknowledged, stress is a killer. Often is asked the question, “Why did my fish die after m months or y years?” when the real question is “Where was stress coming from that cut my pet’s life short?”

    On the other hand, most new aquarists don’t ask these questions because they fear they were the one responsible for the premature fish death. The fact is for the most part, they are.

    It’s a challenging hobby. There are many aspects to the hobby that make or break our success. Every tank is unique in its own way and that makes broad sweeping absolute statements impossible. But I hope the above has provided at least some things deserving your attention.

    Something goes wrong in the tank (e.g., water quality). The aquarist, after an amount of time, sees/notices what is wrong and fixes it. Everything is fine, right? NOT! During the time things were out of wack, the fish was under stress. It lost some of it longevity that the 'fix' will never give back. Stresses accumulate and can't be 'undone.' We have only the opportunity to understand and prevent stresses.

    It's good to remember that in general, marine fish are always growing. They never stop growing. Although your captive fish may not reach its maximum size, it is nonetheless growing. When the fish stops growing or shows no sign of growth, something is wrong and that wrong can be traced to one or more of the above mentioned stress sources. The goal in this hobby is to have fish that thrive, not just survive: Thrive or Survive?.

    Back to the original question in the Intro. Can stress be eliminated? Probably not. But we can get real close to it as evidenced by fish living a healthy 20+ years in captivity.

    Thanks for reading this. [Ending with the song Under Pressure by Queen].

    Some useful references and additional reading:

    Quarantine tank and system:
    An Ounce of Prevention is Worth a Pound of Cure: A Quarantine Tank for Everything by Steven Pro -


    A Quarantine Procedure

    Fish feeding and Nutrition:
    Fish Health Through Proper Nutrition

    Copper as a stress source:
    Copper Medications - Good, Bad, and Ugly

    More technical information about stress:
    Fish Stress – A Technical/Physiological Approach

    Other references and links to them can be found in this post:
    Table of Contents and Link List
    Last edited by leebca; 09-06-2007 at 03:26 PM.

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