The Lake Constance deep-sea char did not fall victim to the era of water pollution, a study confirms: The genetic analysis of discovered specimens with a previously questionable identity has confirmed that they are in fact direct descendants of the species, which was thought to be extinct for a long time. The fish therefore differ significantly from the so-called normal char of Lake Constance. In contrast to the deep-sea char, their stocks have changed significantly in recent decades due to the naturalization of fish from other Alpine lakes, the researchers report.
Today, Lake Constance has exemplary water quality. But that wasn’t always the case: until the middle of the 20th century, until extensive protective measures were introduced, amounts of sewage got into the lake, which led to over-fertilization. This led to algal blooms, which in turn led to oxygen deficiency in the deep water. This primarily harmed fish species that spawn there. One species that only occurs in Lake Constance was particularly affected: stocks of deep-sea char (Salvelinus profundus) collapsed. Up to 28 centimeters long, these fish spawn and live at depths of around 70 to 150 meters. They differ significantly in their behavior and appearance from their relatives, the normal char (Salvelinus umbla), which can grow up to 40 centimeters in size.
Really rediscovered?
While its stocks were still able to survive, the trail of the deep-sea char was finally lost: no specimen had been discovered for more than 40 years – the species was considered extinct. But in 2014, a fisherman made a surprising discovery in his net: he found an unusual-looking char. Scientists from the Langenargen fisheries research center and the Swiss Aquatic Research Institute then discovered further fish in net catches from the depths, which were apparently deep-sea char. But so far, questions have remained unanswered. Because it seemed possible that these are just special forms of the common char that have adapted to life in the depths as the water quality has recovered and are therefore similar to the actual deep-sea char.
In order to provide clarity, the scientists led by Jan Baer from the fisheries research center in Langenargen have now carried out a genetic study. They succeeded in extracting genetic information from specimens of deep-sea char and normal char from historical collections. They were then able to compare these with the genetic characteristics of the possible new finds of deep-sea char.
There were survivors
It turned out that the DNA of the specimens in question is almost identical to the genome of the earlier representatives of deep-sea char living in Lake Constance more than 40 years ago. The researchers were thus able to refute assumptions about a mixing of deep-sea char with normal char or a rapid evolutionary adaptation strategy. The deep-sea char are therefore never really extinct. “Today’s deep-sea char are directly descended from the original specimens. So some animals must have managed to survive undetected in the depths of the lake. Apparently, the calls for help from professional fishermen in the 1950s had an effect: measures taken early on to prevent over-fertilization have resulted in the preservation of the deep-sea char’s habitat,” Baer sums up.
The researchers report that the genetic study also provided interesting insights into the common char: The consequences of the naturalization of specimens from other Alpine lakes, which should serve to increase the stocks under pressure, are clearly becoming apparent. “Our data show what these stocking measures had until the 1990s: The original form of the common char from Lake Constance was almost completely suppressed and largely replaced by a mix of farmed fish,” says co-author Ulrich Schliewen from the Zoological State Collection in Munich.
Source: Bavarian State Natural Science Collections, specialist article: Ecological Applications e2773, doi: 10.1002/eap.2773