Growth measurements in pink salmon (Oncorhynchus gorbuscha) at yolk sac absorption (following ten weeks of CO2 exposure in freshwater). a, Body lengths. b, Production efficiencies (net tissue produced/net yolk consumed × 100). c, Total wet mass. d, Total dry mass. 450–2,000 μatm represents a diurnal cycle and other tensions are constant throughout. Graphic: Ou, et al., 2015

By Niina Heikkinen and ClimateWire
30 June 2015

(ClimateWire) – Pink salmon are providing researchers with sobering hints to how carbon dioxide-induced acidity could affect freshwater fish species by the end of the 21st century.

A study published yesterday in Nature Climate Change showed that early exposure to high levels of CO2 during the larval stage of development had significant negative effects on the fish’s size, metabolism and ability to sense threats in their environment.

The study was among the first to look at how different CO2 levels could affect fish larvae in fresh water, according to the lead author, Michelle Ou, a former master’s student at the University of British Columbia in Vancouver.

“We didn’t actually expect to see so many effects,” she said. “We were just poking around to see what we could find.”

Pink salmon seemed like a good species to start with. Not only are the fish abundant and economically important, but they also serve as a keystone species in marine, freshwater and terrestrial ecosystems, according to the researchers. Although pink salmon spend their adulthood in the open ocean, their first weeks of life are in freshwater streams. Once they have matured from larvae to fry, the fish leave the streams where they hatched and swim to the open ocean. Later, as adults, the fish will return to the same streams to spawn.

Ou and her colleagues at UBC created an experiment to test how fish were responding not only to ambient CO2 concentrations but also to acidity levels expected by 2100.

After obtaining salmon embryos from a hatchery, the researchers transferred them into freshwater flow-through tanks with either ambient, high or variable concentrations of CO2. After 10 weeks, they tested the baby fish to see whether or not their development had been affected by the different conditions.

They found that not only were they smaller and lighter, but the fish’s senses were also impaired. The pink salmon larvae were more bold around new objects and did not seem to be afraid of alarm cues in the water that would normally prompt fish to flee.

The fish also had an impaired sense of smell that prevented them from recognizing specific amino acids associated with the streams where they were born. This was significant because recognition of those amino acids is believed to play an important role in the fish’s navigational ability, said Ou.

“Think of it as a smell fingerprint of their natal stream, and they use that to find their way home,” she said. [more]

Pink Salmon Struggle as Freshwater Becomes Acidic



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