As sea temperatures rise, stocks of some fish species can decline while
others may grow, reveals new research from the University of Gothenburg
looking at gastrointestinal function in fish.
The gastrointestinal system in fish is much more sensitive to temperature
changes than previously believed and may even be a limiting factor for the
distribution of species, a thesis from the University of Gothenburg shows.
The gut could reveal effect of climate change on fish. Image Credit: University of Gothenburg
By looking at how gut function in various fish species is affected by both
rapid and slow changes in water temperature, we can better understand what will
happen to different species when the climate changes.
“When the temperature of the water rises, the fish’s body temperature climbs,
activity in the gut increases, and more energy is needed to stay healthy,” says
researcher Albin Gräns,who has studied various species in both saltwater and
freshwater environments in western Sweden, California and Greenland.
Ectothermic animals are Cold-blooded victims of their environment
Almost all fish are ectothermiccold-blooded, which means that their body
temperature is the same as that of their surroundings. When the temperature of
the water changes, so does the temperature of the fish, which affects all their
body organs.
“Since changes in body temperature affect virtually all of a fish’s organs,
it’s surprising that we know so little about how temperature changes impact on
their physiology,” says Gräns.
Winners and losers
Albin Gräns has studied sculpin, sturgeon and rainbow trout at various
temperatures.
His research shows that some species may find it harder to absorb nutrients
as water temperatures rise, while others could profit from the new climate.
“If the water temperature in the Arctic rises further, some sedentary
immobile species, such as various types of sculpin, will probably struggle to
maintain blood flow in the gut during the summer months, which will affect their
health,” he explains.
Other fish, such as those currently living at the lower extremes of their
possible distribution, could instead benefit from a slightly higher temperature.
The effects of a rise in water temperature will therefore vary between species,
and many of the changes are difficult to predict.
“Our work is largely about trying to identify the physiological bottlenecks,
in other words which parts of the body will fail first – whether the heart or
the gut is the most sensitive part of the system.”
Exploiting temperature differences
Turning food into nutrition requires the gastrointestinal system to function
properly. Fish turn out to have guts that are highly sensitive to changes in
water temperature, and many temperature-regulating behaviours observed in fish
can probably be due to that the fish put down to attempts to maintain or
maximise gastrointestinal function.
“By eating at one temperature and then swimming off to another temperature to
digest the food, fish can exploit areas that might otherwise be harmful to
them,” says Gräns.