Threespine Stickleback, Gasterosteus aculeatus
Threespine Stickleback, Gasterosteus aculeatus, Female. Fish caught from the Pine Valley Creek, Pine Valley, California, March 2018. Length: 5.2 cm (2.0 inches). Catch, photograph and Identification courtesy of Ben Cantrell, San Diego, California.
Threespine Stickleback, Gasterosteus aculeatus, Male. Fish caught from the Pine Valley Creek, Pine Valley, California, March 2018. Length: 5.9 cm (2.3 inches). Catch, photograph and Identification courtesy of Ben Cantrell, San Diego, California.
Threespine Stickleback, Gasterosteus aculeatus, Male. Fish caught from the Pine Valley Creek, Pine Valley, California, March 2018. Length: 5.9 cm (2.3 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
Threespine Stickleback, Gasterosteus aculeatus, Male. Fish caught from a pier in Port Alberni, British Columbia, August 2021. Length: 6.4 cm (2.5 inches). Catch, photograph and identification courtesy of of George Brinkman, Guelph, Ontario, Canada.
Threespine Stickleback, Gasterosteus aculeatus, Male. Fish caught from coastal waters off Santa Cruz, California, September 2023. Length: 7.0 cm (2.8 inches). Catch, photograph and identification courtesy of Ben Cantrell, Peoria, Illinois.
The Threespine Stickleback, Gasterosteus aculeatus, is a member of the Stickleback or Gasterosteidae Family, that is known in Mexico as épinoche à trois épines. The fish is named for the three spines of its dorsal fin. Globally, there are six species in the genus Gasterosteus, two of which are found in Mexican waters of the Pacific Ocean. There are actually two forms of the fish, an anadromous form that lives in the Pacific Ocean and migrates to freshwater streams to reproduce, and the freshwater form that resides full time in freshwater with variation between deep-water and shallow-water lakes. Many taxonomists believe that these two forms should be separated into two or three individual species.
The Threespine Stickleback has an elongated compressed streamlined torpedo shaped small body. They vary in color from a drab olive to a silvery green with brown mottling dorsally transitioning to silver ventrally. Breeding males have red throats, lower head and anterior bellies and blue eyes. Breeding females have throats and bellies that are pink. Their anal fin has 1 short isolated spine and 8 to 11 rays; their caudal fin is straight and the peduncle is slender; their dorsal fin has 3 sharp free spines, the third of which is short, and 10 to 14 rays; their pectoral fins are large with 10 rays; and, their pelvic fins have 1 spine and 1 ray. They have 17 to 27 long and slender gill rakers. The Anadromous form is fully plated with up to 37 plates on their sides, a pronounced keel on each side of the caudal peduncle, long dorsal and pelvic spines. The Fresh Water form has 0 to 12 armored plates and shorter and dorsal and pelvic fins. Their body does not have scales.
The Threespine Stickleback is found in both freshwater, brackish water and coastal marine environments in backwaters, bays, harbors, ditches, lakes, marshes, ponds, and slow-moving rivers, within a few meters of sea level with water temperatures between 4oC (39oF) and 20oC (68oF), at depths up to 100 m (330 feet). In freshwater they are found in vegetated areas; marine populations are pelagic. They reach a maximum length of 11.0 cm (4.3 inches). The Threespine Stickleback is a carnivore that feeds on benthic invertebrates, including crustaceans and larval insects, and zooplankton. In turn they are preyed upon by fish and herons, kingfishers and loons. Reproduction involves nest building with plant materials by the highly territorial males, depositing 40 to 300 eggs by one or more females and fertilization by the male. Each female will typically lay a few hundred eggs and may lay eggs in several nests over a period of several days. The males then chase the females and aerate and guard the eggs for 5 to 10 days until they hatch and the juveniles for two additional weeks. Anadromous forms usually die of exhaustion after spawning cycle. Freshwater individuals are able to complete several cycles within one year or sometimes over several years. The juveniles remain in the nest for a couple of days and then disperse. To avoid predation, they have the ability to lock all spines in place making them difficult to swallow. They have life spans of up to eight years in captivity.
The Threespine Stickleback is a straightforward identification due to the body shape and their three dorsal spine arrangement.
The Threespine Stickleback is a resident of Mexican waters of the Pacific but has a limited range being found from just south of Guerrero Negro, Baja California, northward along the central and northwest coasts of Baja.
From a conservation perspective the Threespine Stickleback is currently considered to be of Least Concern with stable, widely distributed populations. They have been introduced in several states in the United States and their global populations are estimated to be in excess of 1,000,000 individuals. They are prone to eradication in some areas by the introduction of invasive species and human development that destroys their native habitat. They are commonly used as laboratory animals and in public aquariums. They have been utilized on a limited basis in fishmeal and fish oil. The Threespine Stickleback has been a major focus of scientific study including their great morphological variations from location to location, genetic changes involved in adapting to new environments differences between their anadromous form and their freshwater form, tolerance to large salinity changes, and their social behavior that changes radically when breeding.