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A fish's hypoxia tolerance can be represented in different ways. A commonly used representation is the critical O 2 tension (P crit), which is the lowest water O 2 tension (P O 2) at which a fish can maintain a stable O 2 consumption rate (M O 2). [2] A fish with a lower P crit is therefore thought to be more hypoxia-tolerant than a fish with a ...
The model describes how dissolved oxygen (DO) decreases in a river or stream along a certain distance by degradation of biochemical oxygen demand (BOD). The equation was derived by H. W. Streeter, a sanitary engineer, and Earle B. Phelps , a consultant for the U.S. Public Health Service , in 1925, based on field data from the Ohio River .
The term fish kill, known also as fish die-off, refers to a localized mass die-off of fish populations which may also be associated with more generalized mortality of aquatic life. [ 1 ] [ 2 ] The most common cause is reduced oxygen in the water, which in turn may be due to factors such as drought , harmful algal bloom , overpopulation , or a ...
Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce. Most fish and motile organisms tend to emigrate out of the zone as oxygen concentrations fall, and benthic populations may experience severe losses when oxygen concentrations are below 0.5 mg l −1 O 2. [17]
The temperature is 2–3 °C (3.6–5.4 °F) cooler than that of Devils Hole and the dissolved oxygen content is doubled in attempts to reduce thermal and respiratory stress on the fish. [60] The population of Devils Hole pupfish at AMFCF was created by taking eggs from Devils Hole.
Fish need dissolved oxygen to survive, although their tolerance to low oxygen varies among species; in extreme cases of low oxygen, some fish even resort to air gulping. [25] Plants often have to produce aerenchyma, while the shape and size of leaves may also be altered. [26] Conversely, oxygen is fatal to many kinds of anaerobic bacteria. [22]
Hypolimnetic oxygen depletion can lead to both summer and winter "kills". During summer stratification, inputs or organic matter and sedimentation of primary producers can increase rates of respiration in the hypolimnion. If oxygen depletion becomes extreme, aerobic organisms, like fish, may die, resulting in what is known as a "summer kill". [8]
In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange. The muscles on the sides of the pharynx push the oxygen-depleted water out the gill openings. In bony fish, the pumping of oxygen-poor water is aided by a bone that surrounds the gills called the operculum. [6]