Field guide training: Fish – Part 1

Until today, the deep sea is not fully explored, including lots of animals that live there. Especially the group of fish is object of many research projects and expeditions, not only because of their biodiversity (approximately 50% of all living vertebrates on earth), but also due to their importance in the evolution of all land-living vertebrates and, therewith, us humans. Fossils prove that fish have lived in the ocean already 500 million years ago. This leads to the conclusion that all recent vertebrates – no matter if amphibians, reptiles, birds or mammals – originate from fish.

The science which is focusing on the biology and classification of fish is called Ichthyology (Greek Ichthys meaning “Fish” plus -logy). This also includes the behaviour and ecology of this fascination species. Despite many similar main characteristics between most fish species regarding their way of life and their physiology, they have settled in a variety of different habitats. Fish can be found in the deepest parts of the ocean, in lakes with such a high concentration of salt that other animals would not tolerate or ice-cold mountain rivers. Thanks to their adaptiveness they have been very successful in evolution.

Fish are classified by looking at their evolutionary development stages, as well as their feeding and breeding behaviour. The oldest category of fish are the jawless fish, for example the lamprey from which the cartilaginous fish has developed. The best example for cartilaginous fish is probably the group of sharks. Originating from these two categories is the category of bony fish which most fish species belong to.

Marine fish play a minor role during our field guide courses. Therefore, this chapter is focusing on the fish species that live in fresh water.