麻豆淫院

Fossilized fish ear stones鈥攌nown as otoliths鈥攃an reveal far more than previously thought. In a recent study, a team of paleontologists from the University of Vienna demonstrated that a refined electron microscopy technique can make even the finest growth rings visible. These microscopic structures may reflect a fish's life story down to just a few hours鈥攁n important breakthrough for understanding fish growth, biomineralization, and environmental change across millennia. The study was recently in Limnology and Oceanography: Methods.

All fish have tiny mineral structures in their inner ears called otoliths.

"These structures store a fish's entire life story in the form of growth rings鈥攍ike the annual rings of a tree. They can tell us about age, growth phases, and even environmental conditions," explains the leading author Isabella Leonhard from the Department of Paleontology.

In modern marine biology and fisheries research, otoliths have long been essential tools for studying fish growth, migration, and population dynamics. In paleontology, however, they were often overlooked.

"That is beginning to change," says Leonhard, "because new technologies鈥攔anging from high-resolution imaging to chemical analysis鈥攁re making it possible to apply biological methods to fossils that are thousands or even millions of years old." As a result, otoliths are gaining attention in the paleontological community and offer unique insights into ancient fish populations.

'Diary entries' of fishes

Of particular interest are the ultra-fine growth rings in otoliths, which can be read like fish's "diary entries." In fossil specimens, these rings were previously hard to detect鈥攂oth because the material's preservation varies and because traditional light and electron microscopy had reached their limits.

Leonhard and her team adapted a well-established technique from geology to study these growth patterns: Backscatter Electron Imaging (BSE). This method exploits the fact that electrons are reflected differently by different structures within the material, revealing even the most delicate internal patterns.

By fine-tuning the imaging settings, the researchers were able to visualize extremely finely banded growth rings in fossil otoliths from the black goby (Gobius niger), found in the northern Adriatic Sea and buried in the seafloor for over 7,600 years. With this optimized method, they detected up to 275% more growth rings than standard imaging techniques would allow.

"With the electron microscope, we were able to make even the smallest growth increments visible," Leonhard explains. Typically, these rings form in a daily rhythm. In addition, micro-increments exist that form independently of the daily cycle鈥攖hese sub daily patterns reflect feeding, movement, environmental changes, or stressors the fish was exposed to.

"We discovered extremely fine, regularly spaced structures that appear in much shorter intervals than a day. Their pattern suggests they also follow a biological rhythm鈥攂ut we still do not know exactly what causes them," says Emilia Jarochowska, paleontologist and study collaborator from Utrecht University. "Controlled growth experiments will be needed to investigate further."

Using fossil otoliths to understand modern change

This optimized BSE method enables scientists to compare fossil and modern fish populations in unprecedented detail, providing a broader timescale for current changes. "In times of climate change and overfishing, it is crucial to understand how fish populations have developed over long periods," emphasizes Martin Zuschin, head of the Department of Paleontology and a co-author of the study.

"Our results show that fossil otoliths have enormous untapped potential, and can help us to better understand the changes we are seeing today."