After the deep-sea char had disappeared from Lake Constance for more than four decades, scientists caught some specimens of this species in 2014 – which puzzled the researchers for a long time. How might the fish have gone undetected for so long? Or were they descendants of the common char that might adapt to life at depth?
They therefore fished Lake Constance at great depths for several years. In addition to the normal char (Salvelinus cf. umbla), which can be up to 40 centimeters in size, they repeatedly caught specimens of the much smaller deep-sea char (Salvelinus profundus), up to 25 centimeters in size.
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DNA shows some must have survived at depth
In addition, a research group led by Jan Baer from the fisheries research center in Langenargen near Friedrichshafen and Ulrich Schliewen from the Zoological State Collection in Munich succeeded in obtaining usable DNA fragments from the two fish species from historical collections.
As they now report in the journal “Ecological Applications”, the genome of the recently caught deep-sea char is almost identical to that of the fish living in Lake Constance more than 40 years ago. “So some animals must have managed to survive undiscovered in the depths of the lake,” said Baer in a press release from the Munich State Zoological Collection. Apparently, calls for help from commercial fishermen in the 1950s had an effect, says the scientist. Measures taken early on to prevent over-fertilization are likely to have preserved the habitat of the deep-sea char.
No mixing of the two char forms
The researchers also found clear evidence that common and deep-sea char still have vastly different spawning areas and times. Hypotheses on the mixing of the two forms or rapid evolutionary adaptation strategies, such as those employed following the rediscovery of the deep-sea char, would not have been confirmed.
Today’s normal char are a mix of farmed fish
Surprisingly, the genome comparison also showed that the genome of the recently caught common char differs significantly from that of specimens of this species caught decades ago. The scientists attribute this to the stocking measures in Lake Constance with char from all over the world up until the 1990s.
“The original normal form of the char from Lake Constance has been almost completely suppressed and largely replaced by a mix of farmed fish,” says Schliewen. Since stocking other chars is now forbidden, the researchers hope that the last offspring of the original normal char will prevail once more over time.
