Red-tailed Black Shark (Epalzeorhynchos bicolor)
Also known as Labeo bicolor or the redtail shark, the red-tailed black shark is a species of cyprinid endemic to Thailand. Recently thought to be extinct in the wild the biology of the red-tailed black shark is an enigma. Redtail sharks are omnivorous and will feed on plant matter and small invertebrates. Although they are popular in the aquarium trade the red-tailed black shark is critically endangered in the wild, which is thought to be partly due to its popularity in the pet trade and habitat destruction.
Phylogeny
Animalia-Chordata-Actinopterygii-Cypriniformes-Cyprinidae-Epalzeorhynchos-bicolor
Alligator Gar (Atractosteus spatula)
The alligator gar is a large freshwater fish found in sluggish pools in the Lower Mississippi River Valley. The fish can grow up to 3m (10 ft), weighting at least 91kg (200 lb).
The fish has seen a decline in population due to overfishing and habitat destruction. Flood-control measures such as dams and dikes have dramatically altered their riverine ecosystems and largely eliminated their preferred spawning habitats across North America.
David Foster, Charles and Clint on Flickr
Prussian Carp (Carassius gibelio)
The prussian carp is naturally found in northern Asia, although they have been introduced throughout Europe and Asia. It is from these fish that ornamental goldfish were developed though centuries of selective breeding.
Bubble Eye Goldfish (Carassius auratus auratus)
Fancy goldfish varieties are the result of the selective breeding of traits that would normally disadvantage a fish in the wild. In the safe, controlled environment of an aquarium, such traits can be proliferated and emphasised over several generations.
Lerdsuwa on Wikimedia Commons
Origin of the Goldfish
The goldfish (Carassius auratus auratus) you see in pet shops are the result of centuries of selective breeding.
The ancient Chinese have been rearing wild Prussian carp (Carassius gibellio) as food fish for thousands of years. During the Tang Dynasty (618-907), it was popular to raise carp in ornamental ponds. Natural genetic mutation produced individuals that had a yellowish hue to them, which was preferred over the natural silver coloration.
By the Song Dynasty (960-1279), the domestication of goldfish was established. Further genetic mutations caused for stronger oranges, reds and yellows to appear. Because these fish were kept in the safety of a pond, the conspicuous metallic colors did not disadvantage their survival.
The Ming Dynasty (1368-1644) saw the raising of goldfish indoors. This led to the development of many fancy strains, greatly changed from their wild shape. Protruding eyes, double tails and many unusual traits were emphasized through selective breeding, leading to many unique varieties of the one species.
Goldfish are still being developed today, with around 300 breeds recognized in China. Some varieties have been so physically changed that they are unable to survive outside of the aquarium. If introduced to the wild, domesticated goldfish can hybridize with certain species of carp. Within three generations, the hybrid fish revert back to their original coloration.
Images: Viridiflavus, Piet Spaans, Adityamadhav83, ぱたごん on Wikimedia Commons
The threespine stickleback, Gasterosteus aculeatus, is native to northern Europe, northern Asia, and North America. Most populations are anadromous (they live in seawater but breed in freshwater or brackish water), but there are also freshwater populations confined to landlocked lakes
This species has contributed much to the study of species formation and it is a research organism for evolutionary biologists and geneticists studying adaptation to new environments.
More about this fish on EOL: http://eol.org/pages/223856/details
Image by D. Ross Robertson via Shorefishes of the neotropics
Archerfish (Toxotes sp.)
Archerfish are renowned for their amazing ability to shoot water at prey. The fish have a narrow grove on the roof of its mouth, which the fish presses its tongue against to form a channel. It then contracts its gill covers to force water through the channel to form a jet up to 5m long.
An adult archerfish can reliably shoot prey up to 2m away. If the first jet does not knock the prey into the water, the fish will quickly fire a second shot. Accuracy is gained through experience, with young fish hunting in small schools to increase the chance that the prey is hit.
Vailati A, Zinnato L, Cerbino R via Wikimedia Commons
