The stickleback is a small fish distributed across the Northern Hemisphere’s aquatic environments. Its name is derived from the prominent, sharp spines located on its back. These fish have captured the interest of scientists due to their adaptability and observable behaviors. Found in diverse waters, from coastal seas to inland lakes, the stickleback showcases a variety of forms and survival strategies.
Stickleback or Minnow?
Though sometimes referred to as the “stickleback minnow,” this fish is not a true minnow. This common name is a misnomer, as sticklebacks and minnows belong to entirely different scientific families. Sticklebacks are classified under the family Gasterosteidae, while minnows are part of the Cyprinidae family.
The defining characteristic that separates the two is the stickleback’s series of isolated, erectile spines along its back, which minnows lack. The term “stickleback minnow” is a confusing colloquialism that incorrectly groups this fish with a family to which it does not belong.
Physical Characteristics and Habitat
Sticklebacks are recognized by their dorsal spines, which are not connected by a membrane. The most common species, the three-spined stickleback (Gasterosteus aculeatus), has three such spines, though the number can vary. Instead of scales, their bodies are often protected by a series of bony plates on their sides, the number of which can differ between populations. These fish are small, with adults reaching lengths between 6 and 10 centimeters.
This fish demonstrates adaptability, thriving in freshwater, brackish, and marine habitats across the coastal and inland waters of North America, Europe, and Asia. This wide distribution is partly due to their tolerance for varying salinity levels, which allowed them to colonize new freshwater lakes that formed after the last ice age.
Unique Mating and Nesting Behavior
The stickleback’s reproductive cycle has been a subject of extensive study. During the breeding season, the male undergoes a physical transformation, developing bright breeding colors that include a red throat and abdomen, along with iridescent blue eyes. This display serves to attract potential mates. The male then constructs a nest on the riverbed or lake bottom.
He weaves together pieces of vegetation, binding them with a glue-like protein called spiggin, which he secretes from his kidneys. Once the nest is complete, the male performs a “zig-zag dance” to court a female and entice her into the nest. After she deposits her eggs, the male enters to fertilize them and continues his parental duties by guarding the nest and fanning the eggs with his fins to supply oxygenated water until they hatch.
Role in Scientific Research
The stickleback is a model organism in scientific research. Its rapid adaptation to different environments makes it ideal for studying evolutionary processes. For example, scientists have observed how stickleback populations isolated in different freshwater lakes evolved varying numbers of bony armor plates depending on local predation pressure.
The fish has also played a part in ethology, the study of animal behavior. Its distinct courtship rituals provided early researchers with clear examples of instinctual behaviors and helped develop theories about how genetics and environment shape animal actions.