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Sticklebacks are small, lively fish distantly
related to seahorses and pipefish. They are found in streams, ponds,
estuaries and tide pools across North America, Europe and Asia. The
species most commonly kept by hobbyists is Gasterosteus
aculeatus, the Three-Spined Stickleback, so-named for the three
stout dorsal fin spines that they use to defend themselves against
predators. Description and adult size Three-Spined Sticklebacks are distinctive fish
but surprisingly variable nonetheless. Adult specimens are only 6-8
cm/2-3 inches in length, though sometimes specimens can be found that
are a little larger. They have an angular, even bony appearance as well
as the distinctive dorsal and pelvic fin spines. Most specimens have a
series of armoured plates along their flanks, but this trait is
notoriously variable, with freshwater specimens typically having fewer
armour plates than specimens living in brackish water or fully marine
environments. Outside of the breeding season males and females
look alike, greenish-brown above and silver below, but from early
spring through to late summer males become much more colourful as well
as more aggressive. Breeding males are shiny green to blue, have red
across the throat and belly, and have very bright blue eyes. During the
breeding season males guard territories and chase away any rival males.
Outside of the breeding season both males and females school
together. Water chemistry and
temperature Three-Spined Sticklebacks are found in a range of
habitats and to some degree each habitat is home to a particular
variety or subspecies. Marine sticklebacks will not adapt to freshwater
conditions indefinitely, and brackish water sticklebacks tend to be
sickly when maintained in freshwater aquaria. On the other hand, the
freshwater varieties generally adapt well to both hard and soft water,
provided extremes are avoided. Ideally, keep them in water chemistry
conditions similar to those where the Sticklebacks were
collected. They are similarly tolerant of water temperature
fluctuations provided these are not excessive. Sticklebacks can survive
in ponds that freeze over provided the pond is deep enough for a warm
layer to persist under the ice, which means that the pond should be at
least 1 m/3.3 ft. deep, and ideally more. The major problem with hot
summers is the lack of oxygen in warm water, so good water circulation
and the use of waterfalls, fountains, and other aerators will be
useful. Diet Sticklebacks are carnivorous and consume a very
wide range of prey including insect larvae, water fleas, worms, fish
and amphibian eggs, fish fry and tadpoles. Because they are so
predatory they are not good choices for wildlife ponds. They will also
eat any eggs produced by ornamental fish such as goldfish. On the other
hand, they are effective consumers of midge and mosquito
larvae. Social behaviour and
compatibility During winter Sticklebacks of both sexes will
congregate together in loose schools but the rest of the time the males
are territorial and defend their turf vigorously. They can also be
aggressive towards other types of fish, and may damage the fins of
slow-moving fish kept alongside them. Conversely, they are small enough that bigger
fish may view them as prey. Opportunistic fish like Goldfish and Koi
are not able to deal the sharp spines that Sticklebacks possess, and if
swallowed, these clumsy predators can end up getting choked. In short,
Sticklebacks should be kept on their own and in a sufficiently large
pond that aggression between males will be minimised. Expect
territorial males to claim patches around 45 cm/18 inches in
radius. Healthcare Sticklebacks are hardy but they are prone to
protozoan infections similar to those seen among Seahorses, most
notably the microsporidian Glugea anomala. This shows up as
off-white swellings in the muscle tissue, often so large they deform
the fish and can be seen through the skin. There is no treatment for
this highly contagiuous disease, and infected fish should be removed
and humanely destroyed to prevent healthy fish from becoming
infected. One problem in garden ponds is the abundance of
blanketweed and other thick beds of vegetation. Sticklebacks need open
water and have a hard time swimming through plants; if the pond is too
overgrown, Sticklebacks can find their spines catching on the plants so
severely they get tangled up and die. Reproduction Breeding this species is not difficult and in
fact the Three-Spined Stickleback has been a popular lab animal for
decades precisely because it is spawns readily and exhibits fascinating
breeding behaviour. Once the males are in breeding mood, they create
nests from fragments of aquatic vegetation stuck together with a
special gluey secretion they produce from the vent. Egg-laden females
are courted and if the male woos her successfully, she places her eggs
in his nest and he fertilises them. The female is then driven off and
the male looks after the eggs until the fry that emerge are
free-swimming. In a mature pond Stickleback fry will find sufficient food to eat, but the adults can be cannibalistic.
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