Labyrinth
Additional Respiration
Observe closely a typical Labyrinth fish for a few minutes and a particular
pattern of behaviour will quickly become apparent. The fish will be seen to make
frequent and fairly regular visits to the water surface where a gulp of air will
be taken.
If you were now to watch another Labyrinth fish in a different aquarium where
the water temperature was lower or higher, the frequency of surface visits would
be likely to vary.
In what might loosely be described as normal circumstances the fish will
average about four gulps every minute. This will increase where the water
temperature is higher and decrease where lower. The reason for this being that
as the temperature of water rises the quantity of dissolved oxygen within it
reduces. Conversely, cooler water has a greater oxygen content.
It is important to remember that the labyrinth is an auxiliary breathing
system, standard gill respiration also taking place in the usual manner. It
would be true to say that some Labyrinth fish have come to rely on their
supplementary apparatus more than others, but certainly many species would
effectively die from drowning if denied the opportunity of surfacing for too
long.
Why then have these fishes been endowed with a dual breathing system when
most others manage perfectly well simply taking oxygen from the water via gills
in conventional fashion? I say "most others" because labyrinths are in
fact not the only fishes able to take in atmospheric air. They are, however,
with the possible exception of the primitive Lung-fishes, the ones with the most
efficient equipment in this respect.
The answer is, of course, in their natural environment they tend to inhabit
waters seasonally deficient in oxygen. Weed choked ponds and streams, muddy
drainage ditches, flooded paddy fields and clouded irrigation channels are among
the habitats in which they are found. Places where gill reliant species could
not hope to survive!
The labyrinth therefore presents a perfect example of the way evolution,
through radical adaptation and modification, has enabled these fishes to
flourish in an otherwise hostile environment.
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