Phylogeny is the representation of evolutionary relationships, often displayed as a “tree” (i.e., branching diagram) where the most closely related organisms are connected by a node and more distantly related organisms have multiple steps back in the tree before they are connected. Nodes are often characterized by biogeographic events and evolutionary innovations. In fishes, jawless … [Read more…]
Fish population dynamics is the study of change in a fish population over time. Fundamentally, a population size after some time interval equates to the population size before that interval plus births (i.e., recruitment) and immigration and minus mortality and emigration. Many fish populations follow a logistic pattern of density-dependent growth. Beginning with a population … [Read more…]
Phenology is the study of seasonal or periodic cycles in ecosystems. It is, essentially, “nature’s calendar.” For fish, phenology is often linked to timing of important life events such as spawning, migrations, and hatching. These events are triggered by non-biological factors like day length, temperature, and precipitation. If the timing of the main “cue” shifts, … [Read more…]
Panmictic refers to a random mating strategy, frequently employed by fish, where breeding is just as likely to occur between any two individuals in a population as between any two others. Mating in this way is not influenced by any any environmental (e.g., geographic proximity), hereditary (e.g., timing of spawning), or social interaction (e.g., polygamous mating … [Read more…]
Placoid denticles are found on sharks, rays, and chimaeras. Not really a true “scale,” like ctenoid or cycloid scales, placoid denticles are actually modified teeth. They have an inner tissue component, which contains both blood vessels and nerves, that is covered by a layer of dentin and an outer enamel. They form a tough protective skin … [Read more…]
Photophores are organs that are used by fish (and invertebrates) to produce light either by chemical reaction or through symbiotic bacteria capable of bioluminescence. Most fish that use photophores live in the deep sea where light from the surface is limited. Like a firefly in the sea, some of these fish use photophores to attract … [Read more…]
Poikilothermic fish have no control over their body temperature and their core body temperature can fluctuate broadly. While some ectothermic stenotherms thermoregulate their body temperature by inhabiting constant temperature environments, internal temperature of poikilotherms can widely vary.
A potamodromous fish, like an anadromous or catadromous fish, is a migratory fish. Unlike anadromous or catadromous fish, a potamodromous fish spends its whole life in fresh water. Generally, these migrations are for spawning purposes and cover short distances: from an upstream tributary to a mainsteam river or between connected lake and river systems. Some species, for example the … [Read more…]
The pelvic fins are paired fins found on the ventral (bottom) side of fish. In teleost (bony) fishes, pelvic fins placement gives some indication of evolution. For more basal groups, the pelvic fins are located at mid-body in the abdominal region. For more derived fishes, the pelvic fins are located in a thoracic or even … [Read more…]
The pectoral fins are the two fins located on the sides of a fish (or marine mammal). These fins are primarily responsible for control of directional movement, up and down or side to side. Pectoral fins can come in all shapes and sizes which fill different functions for different fish. The pectoral fins of a … [Read more…]