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attempt at brief (?) synopsis of article in FAMA

Posted By: Dr. Momfish <alexp@idirect.com>
Date: Wednesday, 26 January 2000, at 11:34 a.m.

'Understanding and Controlling Stress in Fish' by Terry D. Bartelme FAMA Feb, 2000 pp98-102.

(I don't want to infringe on copyright etc. Everything in parentheses is my 'editor's note'.)

The author introduces the definition of stress as being the response, both physical and phsyiological to a stimulus. Stressors can be acute (short term) or chronic (long term), severe or mild. (Get out the dictionary folks if there are words you don't quite understand. I've done the best I can to explain and translate for those who haven't taken courses in physiology, biochemistry etc. But if you find a word that you really don't understand, please just look it up. Keeping fish is a learning experience after all.)

The impact of stressors is determined by circumstances such as the severity of the stress, how long it lasts, and the general overall health of the fish.

There are three phases to stress response: alarm phase, resistance phase and exhaustion phase.

Alarm phase is the same as when we are almost run over by a bus and adrenalin starts to course through our bodies. It's a fight or flight type reaction. Heart racing etc. In fish, stress releases both catecholamines(adrenalin and noradrenalin) and corticosteroid (cortisol) hormones. The same as in human beings.

During the resistance phase, the hormones stay elevated while the fish attempts to adapt to the stressor.

If the stressor continues for an extended period of time (let's say a fish that is kept at a much lower temperature than to which it can successfully adapt) the exhaustion phase sets in. The fish can then die suddenly. (So can we: heart attacks.)

Catecholamines are more important for acute stressors (like chasing a fish around with a net), and corticosteroids are associated with chronic stress. (Even in human beings, people who have grown up in abusive homes have elevated cortisol levels, usually for life - it can be used as an indicator through a simple blood test. It makes us less resistant to infections and makes those infections more severe than in people who have grown up in 'non dyfunctional' homes. Same applies to fish. Fish raised in crowded ponds etc. are so stressed out, that just shipping them to an lfs results in phenomenal mortality rates.)

A fish under acute stress will increase it's cardiac output, blood sugar levels, respiration rate, oxygen uptake and blood flow to the gills. Once the stressor is removed (i.e. a net) from the environment the fish will recover. However, as anyone who has had a major scare will understand, this type of response results in fatigue because so much energy was used up to deal with it. (You know from your own experience that after a major shock to your own system, the first thing you start doing is trembling and then later, you just want to have a lie down and a nap. Your body has released a lot of glucose into the blood stream to give you the energy to cope. But once the emergency is over, the blood sugar falls and you get a bit of hypoglycemia which makes you feel tired and saps your strength. Now can you imagine how fish in a store tank must feel when, on a daily basis, someone goes in with a net on numerous occasion and chases them around. No bloody wonder they die after a couple of days after purchase.)

Chronic stressors in an aquarium which result in elevated cortisol levels are poor water quality, temperature incompatibilities, overcrowding, incompatibility of species and poor diet.

Responses to stress adversely affect the long term health, growth, reproduction, lifespan and appearance of fish. Energy is used up to cope with stress and is not being utilized for maintaining normal body functions - growth, digestion, osmoregulation, disease resistance, healing and reproduction. 'Because each stress factor drains metabolic energy and increases susceptibility to disease, many of the effects are cumulative.' (Chronic stress ages people too - take a look on the TV when they show refugees who have lived in situations all their lives where they were just getting by, and then now they are displaced, homeless, and have every little thing of their's destroyed.)

Because fish have a much greater dependence on their environment, they are more sensitive to stressors. Gill membranes are especially vulnerable. 'Four important body functions are closely asociated with processes in the gills: gas exchange, hydromineral control, acid-base balance and nitrogenous waste excretion.'

Elevated blood flow in the gills, when the fish is stressed, cause the blood vessels to dilate in order to increase the surface area of the gills for gas exchange. However, at the same time, this allows for excess water to enter the body of the fish. The amount of salt in the body of a freshwater fish is about 100 times that of it's environment. Because of osmotic pressure, water will pass through the gill membranes at a higher rate during stress and 'dilute' the blood of the fish. The fish does have means by which it can concentrate salts in its body, but too much can overwhelm this system.

Under chronic stress, the cell structure of the gills change due to the effect of cortisol. The cell death and renewal rate of gill tissue increases but the newly formed cells do not function normally. Eventually the fish will succumb to osmotic shock and death.

Stress also has an adverse effect on the immune competency of fish and it can result in Delayed Mortality Syndrome. A disease may take advantage of a weakened fish from 2 to 14 days after a shock. Mucus production on the surface decreases as well, so defense against pathogens such as ick or velvet is reduced. The cortisol levels don't have to be majorly elevated in order for the immune system of a fish to be compromised and hence cause a slowing down of response to injury and infection. (Human beings taking cortisone get osteoporosis, poor response to infections or any extra stress.)

Coping with chronic or long-term stress becomes the priority of the fish. As a consequence, it doesn't grow or reproduce. Just trying to maintain itself alive takes up all the energy it has.

Bartelme classifies 4 broad categories for stressors: 1. extreme physical environmental changes - large sudden temperature changes 2. animal interactions - competition for space and food, territorial aggression 3. water pollution - organic chemicals, heavy metals and low pH 4. human interference - handling, overcrowding, transport and netting.

To minimize environmental stressors fish should be kept at their appropriate temperature for species, good nutrition should be provided, and the daily photoperiod should be consistent. (Remember, tropical fish come from a part of the world where the day length doesn't change like it does at higher or lower latitudes. Daylength is 12 hours.)

Crowding causes both acute and chronic stress. Fighting over territory, competition for food and lack of hiding places makes for a very stressful life. Fish kept together must be compatible. If they are not, the incidence of early mortality and disease outbreak increase dramatically. 'Many fish simply cannot survive together in the same aquarium and attempting to force them to do so is akin to a death sentence.'

Water quality: Dissolved organic compounds and the bacterial count in the water result in chronic stress. Hence the need for water changes. (As I've written on LOL before, nitrates and phosphates are just two simple indicators of general water pollution. There are many other substances that we have not tests for.)

Fish are delicate creatures. They have their species specific requirements and these must be met in order for them to live long and healthy lives. Their 'fear' response must be respected and they shouldn't be kept in noisy places where there is a lot of action going by close to the tank. They also require a varied diet in order for them to have everything they need to grow healthy and strong.

(I've tried to condense the information in the article and also bring it 'closer to home' by using illustrations and information on the human condition as well. I hope I've helped to enlarge the scope of understanding for the people on this forum. Empathy and compassion are essential in our lives, for ourselves, others and our fish and other pets too. Be all that you can be. Hug trees if you want. :))

Dr. Momfish, over and out.


 

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