Some possible ideas for a 10 gallon coldwater tank.
Three Spined Sticklebacks
(Gasterosteus aculeatus)
Size: 4-10cm (1"- 4")
Origin: Native to the UK and found in fresh and costal waters around Europe and North Africa, North and Central America and Asia.
Porbably the best known Bristish fish. The name originates from the three spines or stickles found at the front of the dorsal fin. During the breeding season their colours intensify, especailly the males. They construct their 'nest' out of pieces of plant or debris. They can be fussy eaters so ask what they are being feed on before you buy them.
********************************************************************* Fathead or Roseyred Minnow
(Pimephales promelas)
Size: 7-10cm (3"- 4")
Origin North America, Canada and down to some southern states.
These are a peaceful and hardy species. The name refers to the small pad of fleshy tissue on the head of sexually mature males, used in reproduction. The pad is used to keep his eggs clean by gently rubbing them with it. There is the natural coloured fish and an orange-yellow colour form.
You need a licence to keep these outdoors but not to keep them in the indoor aquarium. - Refers to the UK.
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Red Shiner or Rainbow Dace
(Cyprinella lutrensis)
Size: 6-9cm (2"- 3")
Origin: North America-United States.
An active, undemanding, shoaling fish. They will not tolerate poorly oxygenated waters.
You need a licence to keep these outdoors but not to keep them in the indoor aquarium. - Refers to the UK.
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Bitterling (usually the European bitterling)
(Rhodeus sericeus)
Size: 6-8cm (2"- 3")
Origin Central and Eastern Europe, to China.
Bitterling are a wonderful fish. There are a few species, but the two most commonly seen are Rhodeus sericeus and Rhodeus ocellatus. They are a small relative of the carp. They grow between 2-4" and are peaceful fish for a coldwater tank providing some extra colour. But they are best known for their remarkable breeding relationship with the swan mussel. At spawning time the female bitterling lays a few eggs in the breathing hole of each mussel. The male follows and sprays milt over the same places. The mussel's breathing ensures that the eggs are fertalised and get plenty of oxygen during the next three to four weeks. When the young Bitterlings come to leave their adopted parent, they are fully equipped to swim. These fish are easy to feed, in breeding season the males will turn wonderfully colourful, providing the temperature rises to around 22C stimulating the start of breeding.
You need a licence to keep the European Bitterling. - Refers to the UK.
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Common Minnow
(Phoxinus phoxinus)
Size: 6-14cm (2"- 5")
Origin: Native to the UK. Found across Europe and across to Siberia.
There is now a Golden form as well as the natural coloured form. They are an active, hardy, shoaling species. They should be kept in well-circulated and well-oxygenated water.
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Clicker Barb or Topmouth gudgeon
(Pseudorasbora parva)
Size: 8-11cm (3"- 4")
Origin: North-east Asia (now feral in parts of Europe).
They are a shoaling fish that prefers fast, well oxygenated waters. The noise supposedly refers to the noise they make when eating.
You need a licence to own this species. - Refers to the UK.
Some other possibilities would be Fancy Goldfish, Hillstream Loaches or maybe a member of the Garra genus.