In 1819–1820, German biologists Johann Baptist von Spix and Carl Friedrich Philipp von Martius undertook an expedition to Brazil.
They returned home to Europe with many natural objects, including an important collection of the freshwater fish of Brazil, especially of the Amazon River.
Spix, who died in 1826, did not live long enough to work out the history of these fish, and Martius selected Agassiz for this project.
Agassiz threw himself into the work with an enthusiasm that would go on to characterize the rest of his life's work.
The task of describing the Brazilian fish was completed and published in 1829.
This was followed by research into the history of fish found in Lake Neuchâtel.
Enlarging his plans, in 1830, he issued a prospectus of a History of the Freshwater Fish of Central Europe.
In 1839, however,  the first part of this publication appeared, and it was completed in 1842.

In 1832, Agassiz was appointed professor of natural history at the University of Neuchâtel.
The fossil fish in the rock of the surrounding region, the slates of Glarus and the limestones of Monte Bolca, soon attracted his attention.
At the time, very little had been accomplished in their scientific study.
Agassiz, as early as 1829, planned the publication of a work, which more than any other, laid the foundation of his worldwide fame.
Five volumes of his Recherches sur les poissons fossiles (Research on Fossil Fish) were published from 1833 to 1843.
They were magnificently illustrated, chiefly by Joseph Dinkel.
In gathering materials for this work, Agassiz visited the principal museums in Europe, and meeting Cuvier in Paris, he received much encouragement and assistance from him.
They had known him for seven years at the time.

Agassiz found that his palaeontological analyses required a new ichthyological classification.
The fossils he examined rarely showed any traces of the soft tissues of fish, but, instead, consisted chiefly of the teeth, scales, and fins, with the bones being perfectly preserved in comparatively few instances.
He, therefore, adopted a classification that divided fish into four groups: ganoids, placoids, cycloids, and ctenoids, based on the nature of the scales and other dermal appendages.
This did much to improve fish taxonomy, but Aggasiz's classification has since been superseded.

Agassiz needed financial support to continue his work.
The British Association and the Earl of Ellesmere—then Lord Francis Egerton—stepped in to help.
The 1,290 original drawings made for the work were purchased by the Earl, and presented by him to the Geological Society of London.
In 1836, the Wollaston Medal was awarded to Agassiz by the council of that society for his work on fossil ichthyology; and, in 1838, he was elected a foreign member of the Royal Society.
Meanwhile, invertebrate animals engaged his attention.
In 1837, he issued the "Prodrome" of a monograph on the recent and fossil Echinodermata, the first part of which appeared in 1838; in 1839–40, he published two quarto volumes on the fossil echinoderms of Switzerland; and in 1840–45, he issued his Études critiques sur les mollusques fossiles (Critical Studies on Fossil Mollusks).

Before Agassiz's first visit to England in 1834, Hugh Miller and other geologists had brought to light the remarkable fossil fish of the Old Red Sandstone of the northeast of Scotland.
The strange forms of Pterichthys, Coccosteus and other genera were then made known to geologists for the first time.
They were of intense interest to Agassiz, and formed the subject of a monograph by him published in 1844–45: Monographie des poissons fossiles du Vieux Grès Rouge, ou Système Dévonien (Old Red Sandstone) des Îles Britanniques et de Russie (Monograph on Fossil Fish of the Old Red Sandstone, or Devonian System of the British Isles and of Russia).
In the early stages of his career in Neuchatel, Agassiz also made a name for himself as a man who could run a scientific department well.
Under his care, the University of Neuchâtel soon became a leading institution for scientific inquiry.

In 1842–1846, Agassiz iss
In 1819–1820, German biologists Johann Baptist von Spix and Carl Friedrich Philipp von Martius undertook an expedition to Brazil. They returned home to Europe with many natural objects, including an important collection of the freshwater fish of Brazil, especially of the Amazon River. Spix, who died in 1826, did not live long enough to work out the history of these fish, and Martius selected Agassiz for this project. Agassiz threw himself into the work with an enthusiasm that would go on to characterize the rest of his life's work. The task of describing the Brazilian fish was completed and published in 1829. This was followed by research into the history of fish found in Lake Neuchâtel. Enlarging his plans, in 1830, he issued a prospectus of a History of the Freshwater Fish of Central Europe. In 1839, however,  the first part of this publication appeared, and it was completed in 1842.
In 1832, Agassiz was appointed professor of natural history at the University of Neuchâtel. The fossil fish in the rock of the surrounding region, the slates of Glarus and the limestones of Monte Bolca, soon attracted his attention. At the time, very little had been accomplished in their scientific study. Agassiz, as early as 1829, planned the publication of a work, which more than any other, laid the foundation of his worldwide fame. Five volumes of his Recherches sur les poissons fossiles (Research on Fossil Fish) were published from 1833 to 1843. They were magnificently illustrated, chiefly by Joseph Dinkel. In gathering materials for this work, Agassiz visited the principal museums in Europe, and meeting Cuvier in Paris, he received much encouragement and assistance from him. They had known him for seven years at the time.
Agassiz found that his palaeontological analyses required a new ichthyological classification. The fossils he examined rarely showed any traces of the soft tissues of fish, but, instead, consisted chiefly of the teeth, scales, and fins, with the bones being perfectly preserved in comparatively few instances. He, therefore, adopted a classification that divided fish into four groups: ganoids, placoids, cycloids, and ctenoids, based on the nature of the scales and other dermal appendages. This did much to improve fish taxonomy, but Aggasiz's classification has since been superseded.
Agassiz needed financial support to continue his work. The British Association and the Earl of Ellesmere—then Lord Francis Egerton—stepped in to help. The 1,290 original drawings made for the work were purchased by the Earl, and presented by him to the Geological Society of London. In 1836, the Wollaston Medal was awarded to Agassiz by the council of that society for his work on fossil ichthyology; and, in 1838, he was elected a foreign member of the Royal Society. Meanwhile, invertebrate animals engaged his attention. In 1837, he issued the "Prodrome" of a monograph on the recent and fossil Echinodermata, the first part of which appeared in 1838; in 1839–40, he published two quarto volumes on the fossil echinoderms of Switzerland; and in 1840–45, he issued his Études critiques sur les mollusques fossiles (Critical Studies on Fossil Mollusks).
Before Agassiz's first visit to England in 1834, Hugh Miller and other geologists had brought to light the remarkable fossil fish of the Old Red Sandstone of the northeast of Scotland. The strange forms of Pterichthys, Coccosteus and other genera were then made known to geologists for the first time. They were of intense interest to Agassiz, and formed the subject of a monograph by him published in 1844–45: Monographie des poissons fossiles du Vieux Grès Rouge, ou Système Dévonien (Old Red Sandstone) des Îles Britanniques et de Russie (Monograph on Fossil Fish of the Old Red Sandstone, or Devonian System of the British Isles and of Russia). In the early stages of his career in Neuchatel, Agassiz also made a name for himself as a man who could run a scientific department well. Under his care, the University of Neuchâtel soon became a leading institution for scientific inquiry.
In 1842–1846, Agassiz iss
Louis Agassiz