Date: February 5th, 10:20am
Today's fish of the day is the Three-spined stickleback!
The three-spined stickleback, also known by scientific name Gasterosteus aculeatus, is a common fish in the Northern Hemispheres Pacific and Atlantic oceans with a near global distribution. Ranging in the Pacific ocean from The coasts of Alaska to Baja California, and then from as far North as Japan and stretching South toward North Korea.
On the Atlantic coast this fish's range stretches from Chesapeake bay down to Baffin island and Hudson bay, stretching across the ocean and populating England and the coasts of Western Europe. Living in shallow and slow moving waters with mud, sand, or gravel bottoms and heavy vegetation and substrate. The three-spined stickleback is known as anadromous, meaning that they can move between salt and freshwater, although there are populations of fish within both regions, with fully freshwater fish growing larger on average, and the saltwater fish moving inward to freshwater for spawning.
Three spined sticklebacks are small, with most only 3-5cm, and freshwater populations occasionally reaching as large as 8cm. As the name may suggest, they have 3 spines on the place of the dorsal fin, which are used in signaling, defense, and offense. They're olive to dark green on the back and sides, with white underbellies and colorless fins, with these colors changing for breeding and spawning season. The diet of the three spined is varied by the environment and population they live in, and then varied further by if the fish is a limnetic or benthic fish. Limnetic (meaning fish living in the uppermost and open water areas) three spined stickleback specialize on zooplankton, whereas benthic (meaning or relating to the bottom or bed of a body of water) tend to attack other benthic organisms.
The general diet listed for these fish when not specified by ecotype is crustaceans, worms, copepods, larvae, small fish, plankton, and algae's. They are regularly predated on by larger fish and water birds, but have a series of defensive measures against these. The spine on their back can be used defensively, as they are quite sharp, along with this, when threatened the three-spined will raise its spines and open its mouth pointing its head downward and make jerky motions. These methods seem relatively effective for warding predators. Other than this, they also have a defensive measure referred to as tit for tat. The tit for tat method, (sometimes called TFT) is when the three spined stickleback tends to copy the behavior of predators it comes in contact with. Especially various trout, as on occasion these salmonoids will "cooperate" with the three-spined, backing off from their territory rather than further instigation. If the opposing fish does not cooperate with the three-spined then the stickleback will mirror every aggressive move until the fish is either intimidated, or fight until its won or died. The last of their defensive measures is to attempt travel with a partner when not in schools, thus each can watch each others back and if one of them get eaten, the other can survive by fleeing (this behavior is only shown by some populations).
In the breeding season, from early spring to late summer, these fish will drastically change in color. Males will get a red underside with blue sides, and their eye change to a striking green/blue color. In females however, they gain a silver underside and a darker green/brown back. During the breeding season male three-spined sticklebacks grow incredibly territory, claiming areas of slow moving freshwater streams with gravel at a temperature between 23-24 degrees Celsius. These fish will then create nests out of mucus threads, which they weigh down with pebbles.
Courting occurs when female fish with eggs enter into a males territory. He will then do a "dance" in front of her where he darts in a zig-zag motion in front of her, he will then entice her into his nest by repeatedly entering and exiting until she is seduced to lay a portion of her eggs within it, anywhere from 5-300 of them. She will then go on to lay the rest of her eggs throughout a multitude of nests, with many males.
These fertilized eggs will remain guarded and ventilated in the nest for around 6 to 8 days, during which the male will leave only to eats the fertilized eggs of other male stickleback fish in the nearby water. After this period, the uneaten eggs will hatch into fry, which are immediately abandoned by their father. Fry will then go on to join a school or shoal of the various fry in the area, and grow into juveniles in the stream fro around a month before venturing out into other streams or the ocean dependent on population. A majority of these fish will live only a year, dying shortly after having children, although a section of them will live around 2-3 years total.
Fossil data tells us that the three spined stickleback has existed almost identical to the form it is in now for 10 million years, and was split from the same ancestor as the blackspotted stickleback. Despite this, there are extreme cases of subspecies, ecotypes, and differences between populations. There is evidence to suggest that the oceanic anadromous fish and the freshwater one should be considered separate lineages. These seem to be kept separate because oceanic saltwater fish breed in the late spring, where freshwater exclusive fish seem to breed in the early to mid summer instead. Even without acknowledging the differences between oceanic and freshwater forms of stickleback (the largest and most obvious change being oceanic fish have some armored scales similar to that of a sturgeon of plecostomus, where freshwater lacks this), there are several differences between populations of sticklebacks such as diet, coloration, behavior, courting techniques, or nest building technique. Another difference between three-spined sticklebacks is their many subspecies.
There are several subspecies, with differing articles stating differing numbers, but as far as I have research there appears to only be three named currently. The first is G. a. aculeatus which is the most widespread and well known, sometimes considered to be the "base" species so to say. This subspecies has many differing names locally across its populations in the Northern hemisphere, but one of the strangest names would be that in England the three-spined stickleback is called tiddlebat, or tiddler.
There is also G. a. williamsoni, also called the unarmored three-spine stickleback, which is found only in some freshwater streams of California, Oregon, British Columbia, and Mexico; found in the Columbia and Colorado river systems.
Then, the last one is G. a. santaeannae or the Santa Ana stickleback, found only in some small streams around Southern California. Despite these many differences, this fish has an amazing ability to evolve and change. For example, in one area of Alaska it was documented that the local population of three-spined sticklebacks went from near 100% oceanic form to 11% oceanic form over the course of only 12 years when the algae, plankton, and small fish amounts increased in freshwater. What a wonderful animal.
That's the three-spined stickleback, everyone! Have a wonderful day, and remember our fishy friends in a river near you!
Sources:
University of California, D. of A. and N. R. (n.d.). California fish species. California Fish Website.https://calfish.ucdavis.edu/species/?uid=101&ds=241
Pacific, A. of the. (n.d.). Threespine Stickleback. Aquarium of the Pacific - A Non-profit Organization.https://www.aquariumofpacific.org/onlinelearningcenter/species/threespine_stickleback
Wood, S. (n.d.). Gasterosteus aculeatus. Animal Diversity Web.https://animaldiversity.org/accounts/Gasterosteus_aculeatus/
Threespine Stickleback (Gasterosteus aculeatus) - species profile. (n.d.).https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=702
Gasterosteus Aculeatus Summary Page. FishBase. (n.d.).https://