Detection and measurement of stress in fish

The intensification of aquaculture practices has increased the levels of stress in fish.
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All groups of zebrafish under confinement also had a greater percentage of occupation of tank areas at more than 28°C for the first 4 h than control groups (Mann–Whitney test; p ). Four hours after the confinement event, a progressive shift to a lower preferred temperatures was observed. Distribution values, similar to control groups, were obtained 8 h after the stressor was applied (fitted polynomial curves for the distribution each hour are depicted in ).
A new approach of monitoring “actual stress” in fish in real time by using biosensor.
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Temperature stress, particularly a sharp decrease in temperature, severely impairs the fish's ability to quickly release antibodies against an invading organism. The time lapse required to mount an antibody response gives the invader time to reproduce and build up its numbers, thereby giving it an advantage which may allow it to overwhelm the fish. Exposure to pH 5.0 and 10.0 on zebrafish exerted stresses with reference to seasons.
Photo provided by FlickrSymptoms: You should observe your fish often for any of these signs of stress.
Photo provided by FlickrAcute exposure of fingerling-aged fish to agrichemicals chronic inhibits stress response.
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Most fish can tolerate environmental conditions that differsomewhat from the natural conditions in which they evolved. This doesnot mean, however, that they will be as healthy or live their fullnormal life span. For example, keeping a fish in water that is cooler(or warmer) than its preferred condition forces its body organs towork harder to keep it alive. That is, such conditions place the fishunder increased stress.The water temperature of your tank should match the needs of itsinhabitants. Keeping water temperature too cold or too warm for aparticular species will stress those fish. For example, goldfishprefer cooler temperatures (under 70F) than most tropical fish(goldfish survive winters in ponds where temperatures approachfreezing), guaranteeing that a tank containing both goldfish andtropicals will either be too cold or too warm for some of theinhabitants.It should be noted that eliminating stress does not guarantee thatyour tank will be healthy. But it significantly increases theodds. Many netters boast regularly about how they've kept fish(apparently) ``healthy and happy'' for long periods of time under(apparently) highly stressful conditions. Such aquarists are sittingon a time-bomb; the not uncommon followup story will refer to one fishgetting sick, then another, with an end result of multiple fishdeaths. Reducing stress simply increases the likelihood that a tankwill stay healthy (much the same way as eating right, exercising andgetting the proper amount sleep is generally associated with a longhealthy life for humans).In this section, we list some of the more common stress-inducingconditions. In all cases, the level of stress induced by a specificfactor is highly species-dependent. You shouldbe aware of the type of stress that will be present in your tanks andselect fish known to tolerate such conditions well. For example, ifyour water is hard and alkaline, you're best off selecting fish thatthrive under such conditions.Not all species of fish mix well with others. As an obviousexample, most cichlids will eat smaller tank inhabitants (e.g.,anything they can fit in their mouths). Even if too big to be eaten,however, peaceful fish will be stressed if kept with aggressive fishthat chase them around all day. Moreover, many fish communicatethrough behavior and body language (i.e., cichlids frequentlyestablish a ``pecking order'' in which one fish is king). Fish of onetype of species may not recognize the signals given off by others,guaranteeing continual strife.