Three-Spined Stickleback Fish (Gasterosteus aculatus)

Three-Spined Stickleback Fish (Gasterosteus aculatus)

 

Japanese Three-spined Stickleback Fish (Taken by Hooper from The Japan Times, 2006)

A. Morphology and Morphometry

1. Morphology

The Three-spined stickleback have a laterally compressed body. The base of the tail is slender. In front of the dorsal fin is three spines, a characteristic that give the fish its name (although, some individuals may have two or four spines). The third spine (the closest one to the dorsal fin) is shorter than the other two. Each spine is joined to the body by a thin membrane on the back. The anal fin is preceded by a short spine, and the pelvic fins consist of one spine each. All spines can be locked in erect position, making the fish extremely hard to swallow by a predator. This fish has large pectoral fins. The body has no scales, but is protected by bony plates (scutes) on the back, flanks, and ventral.

Dorsal part has varies coloration, but tends toward a weak olive or a silvery green color, sometimes with brown stripes. The flanks and belly are silvery. During the breeding season, the males’ eyes become blue and the lower head, throat, and anterior belly turn bright red (male fish produces color from carotenoid when matured). The breeding females’ throat and belly can turn slightly pink. A few populations, however, have breeding males which are all black or all white.

2. Morphometry

The adult sticklebacks can reach lengths of 6-10 cm, but commonly lengths of 3–4 cm (1.2–1.6 in) at maturity phase. The caudal fin has 12 rays. The dorsal fin has 10–14 rays with three spines (vary in certain individuals) in front of it. The anal fin has 8 to 11 rays. The pelvic fins consist of only 1 spine and 1 ray. The pectoral fins has 10 rays and large in size. They usually have 30-40 bony plates on the lateral part of their body. Only one ventral plate is present, but the number of lateral plates varies across the distribution range and across habitat types, however, it is normally higher in marine populations (some freshwater populations may absolutely lack of lateral plates).

B. Habitat and Distribution

1. Habitat and Water Conditions

The three-spined stickleback is an anadroumus type that can live in either fresh, brackish, or sea water - proving their immense salinity tolerance. They prefer slow-flowing water with emerging vegetation. They can be found in ponds, lakes, dams, quiet rivers, bays, marshes, harbours, and even ditches.

2. Distribution

The three-spined stickleback is found only in the Northern Hemisphere, where they usually inhabit calm coastal waters or freshwater bodies. In North America, it ranges along the East Coast from Chesapeake Bay to the southern half of Baffin Island and the western shore of Hudson Bay, and along the West Coast from southern California to the western shore of Alaska and the Aleutian Islands. They also can be found throughout Europe between 35 and 70°N. In Asia, the distribution stretches from Japan (from Hokkaido to Honshu) and the Korean peninsula to the Bering Straits.

3. IUCN Status

According to IUCN red list status (2015), Three-spined stickle back is among the Least Concern (LC) criteria. This species has an extremely broad native distribution, with a large number of subpopulations. This species is not known to be impacted by any major threat processes and is reported to be common to abundant throughout most of its distribution. However, the species has been listed as threatened in some of its range states, for example it is listed as Endangered in Croatia.

Some “species” probably endangered according to evolutionary biologists, who often define “species” as populations that do not interbreed with each other, which means the benthic and limnetic species within a lake would considered as separate species. These species pairs are an excellent example of how adaptation to different environments (in this case feeding in the surface waters or on the lake bed) can generate new species. This process has come to be termed as ecological speciation. This type of species pair is found in British Columbia. Sadly, the pair in Hadley Lake on Lasqueti Island was destroyed in the mid 1980s by the introduction of a predatory catfish, and the pair in Enos Lake on Vancouver Island has started to interbreed and are no longer two distinct species. The two remaining pairs are on Texada Island, in Paxton Lake and Priest Lake, and they are listed as Endangered in the Canadian Species at Risk Act

C. Salinity Tolerance Ability

The three-spined stickleback fish can be divided into 2 rough categories : anadromous and stream-resident.

1. Seawater Tolerance

As an euryhaline fish, the three-spined stickleback has a good capability to adapts different salinity levels. Gasterosteus aculeatus encompasses the coastal waters of Eurasia, Iceland, eastern Asia and Northern America, which means they can adapt to majority of seawater salinity diverse. However, the stream-resident stickleback’s adaptation to seawater is not as good as the anadromous one. Based on a study about the relation between relaxin-related gene expression to stickleback’s osmoregulation by Kusakabe et.al. (2014), the transcript levels of relaxin family peptide in anadromous stickleback were higher than stream-resident stickleback. Those proved that anadomous stickleback are much better in salinity signaling rather than stream-resident stickleback.

2. Freshwater Tolerance

The threespine stickleback is an anadromous type of fish. They spend their juvenile phase in fresh or brackish water and they will be back for spawning eggs. Their type of living habitat is mainly a calm freshwater area with soft substrates (sand, mud, peat, etc.) water bed. However, not all stickleback subspecies have the same capabilities to adapt freshwater. According to Ishikawa et.al.(2016), their research showed that the Japan Sea lineage stickleback have a significantly higher mortality rate than the Pacific Ocean lineage when challenged by freshwater exposure. The prolactin gene, a gene that encodes an important hormone for freshwater osmoregulation, was higher in the Pacific Ocean lineage rather than the Japan Sea lineage.

3. Stickleback as Fish Osmoregulatory Research Subject

The stickleback fish is long known as a scientific subject for many research. They show large morphological variation, ideal for study about fish evolution and population genetics. Most populations are anadromous and very tolerant of salinity fluctuations, a subject of interest by fisheries physiologists. Other reasons why the three-spined stickleback is often used as a study subject are they easy to find, spreads across the world, and easy to keep in aquaria or other fish containers.

D. Life and Reproduction

1. Diet

The three-spined stickleback species may have different feed behaviors, they can be bottom feeder or planktonic feeder, or both. They also can eat insect larvaes, worms, organic debris, algae, and sometimes fish eggs (they can cannibalize their own eggs and fries).

2. Life Cycle

Many populations of three-spined sticklebacks take two-three years to mature and only experience one breeding season before dying. However, some freshwater species and population species at extreme latitudes can reach maturity in one year. This fish life cycle is originating from the fresh or brackish water from fry to juvenile phase. After several days, they will move to the seawater and spend most of their lifetime there. Adult fish will be back to fresh or brackish water as they reach maturity. They will spawn eggs and begin to reproduces there.

3. Reproduction

Reproduction process began from late April, when males and females move from deeper waters to shallow areas. Each male defends a territory where he builds a nest on the bottom. Male fish starts by dig a small pit by his mouth, then he fills it with plant materials (often filamentous algae), sand, and various debris. He glues the pile of nest materials together with a substance called spiggin, a proteinaceous substance secreted from the kidneys. He then creates a tunnel under the nest by swimming vigorously through the subtrate. Nest building basically takes 5–6 hours, though it may be until several days. After this, the male courts a gravid female that pass by with a fast zigzag dance. He approaches a female by swimming in short distances left and right, and then swims back to the nest in the same way. If the female follows, the male often pokes his head inside the nest, and swim through the tunnel. The female then swims through the tunnel as well, where she deposits 40–300 eggs. The male follows to fertilize the eggs. The female is then chased away by the male. For the duration of the eggs' development, the male will chase away other males and non-gravid females. However, he may court other gravid females (more than one batch of eggs can be deposited in the same nest).

The male fish will acts as a sole parental care father. He lines himself up with the nest tunnel entrance and swims on the spot. The movement of his pectoral fins fans a small current of water through the nest, bringing fresh and well-oxygenated water to the eggs. He does this not only during the day, but the night as well. Fanning levels tend to increase until the eggs are about to hatch or when the water is poorly oxygenated, which takes about 7–8 days at 18–20 oC temperature. Towards the end of the egg development phase, the male often makes holes in the roof and near the rim of the nest. This acts presumably to improve ventilation for fanning the nest during a time when the eggs are more metabolically active. Once the fries hatch, the male attempts to keep them together for a few days, sucking up any wanderers into his mouth and spitting them back into the nest. Afterwards, the young fish disperse, and the nest is either abandoned by the male or repaired for another breeding cycle.

References

Kusakabe, M., A. Ishikawa, and J. Kitano. 2014. Relaxin-related gene expression differs between anadromous and stream-resident stickleback (Gasterosteus aculeatus) following seawater transfer. General and Comparative Endocrinology, 205: 197-206.

Ishikawa, A., M. Kusakabe, M. Kume, and J. Kitano. 2016. Comparison of Freshwater Tolerance Between Two Sympatric Japanese Marine Three-spined Stickleback species. Evol Ecol Res, 17 : 525-534.

Hooper, R. 2006.  The Three-spined Stickleback. The Japan Times article (Link)

IUCN Red List. 2015. Gasterosteus aculeatus. (Link).