Fish are easily stressed by handling, grading and transporting. The major concerns in transporting Koi are the management of handling stress, mechanical shock, heat stress and water quality. Stress is typically not a single phenomenon and can vary in intensity. Stress can have a chemical cause or a physical cause. Just a perceived threat can also trigger a stress response. Koi display a wide variation in their physiological responses to stress, which is evident in the hormonal (adrenalin) and cortisol changes that occur following a stressful event. Adrenalin changes are typically an immediate response to stress and cause increases in cardiac output, blood sugar, respiration, oxygen uptake, and blood flow to the gills. Cortisol changes are typically a response to chronic stress and affect the Koi’s osmotic balance and metabolism. A single stressor may thus reduce the capacity of Koi to tolerate subsequent or additional stressors.
Ammonia is the final product of nitrogen metabolism in fish, and most of it is eliminated through the gills into the water. Even fasted fish still produce ammonia, but to a much smaller extent. Ammonia exists in two molecular forms: the NH3 molecule and the NH4+ ionic molecule. The ratio of these 2 forms depends on the pH and water temperature. The Koi’s gill epithelial cell walls are comparatively impermeable to the ammonia ion, but molecular ammonia (NH3) easily penetrates, and thus is toxic. The transport water pH tends to decrease and the water should be at a cool temperature. Under these conditions the ammonia in the transport water is mostly in the NH4+ ionic form, and as a consequence, ammonia toxicity during transport should be less of a problem. Existing ammonia passes from the water through the gills to the blood and then into the tissues. Koi subjected to ammonia will exhibit nervous symptoms . Both higher pH and higher temperature increases ammonia toxicity. If the ammonia level in the blood increases, it may eventually reach a fatal level. This condition is called ammonia autointoxication. The less ammonia there is in the bloodstream of the Koi, the less likely it is that ammonia autointoxication can occur. Various extremes in water parameters, toxins and stress can cause morphological changes to the gill structure and thus reduce its ability to eliminate ammonia. The gill structure can also be damaged by parasites, bacterial, viral and fungal diseases. The metabolic level of Koi can be reduced by cold water temperatures or the use of anesthesia. At low metabolic levels, respiration is reduced and so is the ammonia elimination rate. It is therefore suggested that the possibility of ammonia autointoxication should be reduced by the following guidelines:
- Fully fast Koi for a week prior to transport.
- Do not use anesthetics in transport water.
- Do not transport Koi in cooled water when not fully fasted.
- Maintain high water quality during transport by:
- Neutralizing gill damaging agents like chlorine
- Binding ammonia during transport.
- Minimize stress to Koi during the entire transport process.
- Do not transport Koi with existing gill damage.
- Neutralizing gill damaging agents like chlorine
Transport Water Composition Changes
Poor water quality can cause physical impairment, such as damage to the gills caused by ammonia, and bleeding from the gills. The chemistry of the water within the bag is more complicated than simply the ammonia level, because the toxicity is linked to the pH. As the Koi breathe, more and more CO2 is trapped and builds up in the bag and it is converted into carbonic acid. This causes the pH to decrease. Because there is much less of the toxic component of the ammonia at the ever decreasing pH in the bag, Koi can actually survive a much higher ammonia level while shipping than they could in the pond. When transport water is tested after a 24 hour trip, the ammonia level may be very high and the pH may be very low. Koi can survive this due to the small amount of toxic ammonia at the low pH. Floating the bag before opening it helps Koi adapt to any change in water temperatures. When the bag is opened, CO2 de-gas into the air and causes an upward pH shift and a subsequent increase in ammonia toxicity. That is why Koi should be removed from the bag promptly after it is opened. Some references suggest that pH should also be equalized between the new tank/pond and the bag water, but the damage done by the exposure to ammonia far exceeds the stress incurred by rapidly changing pH.
Controlling Variations in Water Parameters
Water quality parameters can differ significantly from the starting pond to the final pond or tank. Additionally, the parameters in the transport container are constantly degrading with time. Changes in water quality are one source of stress during and after transport. A water additive that contains a buffer will help to reduce stress by controlling the pH shift during transport and is beneficial so long as the ammonia being produced by the Koi is bound (by another chemical) as soon as it appears . An ice pack that is insulated and taped to the top of the shipping box will help to keep a cooler water temperature, which is also beneficial in reducing stress. The use of an ice pack is however subject to conditions
Delayed Mortality Syndrome (DMS)
Rapid changes in water parameters, including pH, temperature and hardness, can stress Koi even if the changes are within the Koi’s normal range of adaptation. Adding the stress caused by relatively small water quality changes to the stress caused by netting, confining and transporting Koi can result in death. Although the Koi may survive the transport and seem fine in the new environment, they can become sick several days to even weeks later. This is called Delayed Mortality Syndrome. It is often associated with opportunistic infections which take advantage of the stressed Koi’s diminished immune system. It is therefore prudent to quarantine Koi after shipping. During that time, Koi should be closely inspected for disease, and water may be salted to 0.3% in order to ease the osmoregulatory load so that the Koi have more energy reserves that they can utilize for healing.
Other Indications of Stress in Koi
Stress can manifest itself differently in each Koi. Stress may be exhibited in Koi as general redness in the Koi’s skin, fins or bleeding from the gills. Stress causes capillaries to become visible because they are engorged with blood due to increased blood pressure. It can be seen as overall redness or red veining in the white skin of the Koi. Some Koi bleed from their gills during a particularly stressful event. While neither of these symptoms will kill Koi directly, they indicate the extent of the problem. One indicator of a Koi’s stress level is the level of cortisol in the blood. Cortisol levels in the blood increase after stressful situations, and significant mortality rates may occur. Cortisol levels may take up to 60 hours to return to normal. During the period of elevated cortisol, the Koi will have a compromised immune system and may succumb to parasites, bacteria or fungus in the water. Stress also increases the permeability of the surface epithelium, including the gills, to water and ions, and thus induces systemic osmoregulation disturbances. The effects of such an osmotic imbalance can result in what is termed as “noninfectious dropsy”, a condition where the fish bloats. The Koi can return to a more normal conformation when placed in a 0,6% salt solution.
Increased permeability of the gills is one of the main reasons for the high vulnerability of fish to water pollutants. The stress response in fish includes an increase in the oxygen uptake rate of the gills. Stress that is severe or chronic can cause harmful physical changes in the gill structure.
Additional stress may be fatal while the Koi is in a weakened state from a previous stressor, and as discussed earlier, stress may be thought of as cumulative. Koi do adapt to stress, but it is recommended not to ship Koi more often than every 3 months. Simply moving Koi within a premise does not constitute shipping, and the 3-month time period does not apply. Unless the health of the Koi is in peril, do not move Koi more often than every 3 days within premises, in order for the cortisol levels to return to normal.
General Adaptation Syndrome (GAS)
This syndrome is divided into three phases: the alarm reaction when stress hormones are released; a stage of resistance during which adaptation occurs; and if the Koi cannot adapt, a stage of exhaustion followed by death. The stress response may be both adaptive and maladaptive. For example, a primary response to stress is the release of cortisol. It makes the gills more permeable and allows for increased oxygen uptake. The fish have adapted by obtaining more oxygen from their gills when the body needs it for a fight or flight response. When the stress is severe or long lasting, the increased permeability of the gills results in electrolyte loss and increased water uptake. Thus, the stress response that was initially helpful, now becomes maladaptive, and threatens the fish’s life. Koi can easily adapt to all sizes of ponds and holding tanks as well as to a wide variety of water quality parameters. It is also possible to preclude the alarm reaction by having the Koi already adapted to netting and confinement before transport. Koi can easily be de-sensitized to nets by simply leaving the nets in the pond for a time. Next, the nets should be slowly moved to a slightly different location on a daily basis. Once the net movement does not cause alarm, the fish can be netted and released without stress.
Once Koi learn to accept netting, the lessons must be reinforced at least once a month. If the time is taken to adapt Koi to being netted, the Koi will be much less stressed by transport and even showing. During the training process, all Koi must be closely observed for disease. The goal is to adapt the Koi to stress slowly, so they do not succumb to parasites or other pathogens. If any of the Koi become ill during desensitization, or show excessive resistance to netting, such as bleeding from the gills (a stress indicator), the desensitization process should be halted and only re-started when all the Koi have recuperated.
Last Updated on Thursday, 27 November 2008 16:29