Lotic refers to freshwater ecosystems involving flowing water, such as a river, stream, brook or creek. Certain fish species are lotic specialists and have evolved to live in higher flow water, such as darters which prefer to live in swift-moving riffles.
Lentic describes freshwater ecosystems characterized by still water and low flow, such as a lake or pond. Certain fish species have evolved to become lentic specialists, such as the high diversity of cichlid species found in Lake Victoria.
The lateral line is, literally, an observable line down both sides of a fish. It is also a sensory organ system that helps fish detect motion in the water around them. When water along the lateral line is displaced by movement or a vibration nearby, hair cells (similar in form and function to hair cells in a human ear) translate the displacement into an electrical impulse that is transmitted to the brain. The lateral line helps a fish orient itself upright in the water and relative to other fish (e.g., schooling fish or predators and prey).
The length of a fish is often used for fish population assessments (e.g., length-age and weight-length relationships) and consequently are often used in recreational fishing regulations. But, just as there is “more than one way to skin a cat,” there is more than one way to measure the length of a fish. Below are three of the most commonly used metrics for measuring fish length:
- Standard length: A fish’s body length from the tip of its nose to end of its last vertebrae. Standard length includes everything except the caudal fin. This measure is used for most bony fish for which the last vertebrae is distinguishable.
- Fork length: The length of a fish from the tip of its nose to the middle caudal fin rays. This measure is best suited for fish that have forked caudal fins.
- Total length: The length of a fish from the tip of its nose to the end of the longer lobe of its caudal fin. This measure is primarily used for fish that have uneven caudal fin lobes, such as hagfish, lampreys, sharks, and rays.
For a comparison of the three length measurements, please review Kahn et al. 2004.
The littoral zone is the region of a body of water (lake, river, or ocean) that is near the shore. While there is no exact definition of the zone, in marine systems it is generally considered to extend from the high-water mark to the continental shelf; freshwater systems it is generally considered to be wetland zones where sunlight can still reach rooted plants. Because of its close association with terrestrial systems, the littoral zone is nutrient rich and highly productive. Fish in these areas, like coral reef fishes, for example, often become highly specialized feeders because of the diverse and abundant food sources.