By the way, I see you found the link to the PETA website! You know, if you're going to use their words verbatim, you should really cite it.
Here's exactly the same passage from PETA, at this link:
http://www.peta-online.org/mc/facts/fsc18.html
Factsheets > Companion Animals
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Fish in Tanks: No Thanks!
Fragile tropical fish, born to dwell in the majestic seas and forage among brilliantly colored coral reefs, suffer miserably when forced to spend their lives enclosed in glass aquariums. Robbed of their natural habitat, denied the space to roam, they must swim and reswim the same empty cubic inches.
Breeders and Dealers: Pain Profiteers
The popularity of keeping tropical fish has created a virtually unregulated industry based on catching and breeding as many fish as possible, with little regard for the fish themselves.
In the Philippines, the source of most saltwater fish sold in the U.S., many fish divers collect their prey by squirting cyanide or other poisons into the coral reefs where fish live.(1) Meant to stun them so that they will drift out of the reef for easy collection, the cyanide kills as many as half of the fish on the spot. Many others die from cyanide residue after being purchased. The poison also kills the live coral where the fish live, which can take thousands of years to grow back.(2)
Most of the freshwater fish sold in the U.S. are easier to breed than their saltwater cousins and are bred on "fish farms." These breeding centers, seeking new market niches, create fish breeds that would never occur in nature. Treating fish as ornaments instead of as live animals, some fish breeders "paint" fish by injecting fluorescent dye into their bodies to make them more attractive to buyers.(3)
Fish Facts
Fish are wonderful creatures with individual personalities and attributes that most people know little about. They communicate with each other, form bonds, and grieve when their companions die.(4) Fish communicate with one another through a range of low-frequency sounds—from buzzes and clicks to yelps and sobs. The sounds, audible to humans only with special instruments, communicate emotional states such as courtship, alarm, or submission.(5) Sadly, the pumps and filters necessary in many home aquariums can interfere with this communication. "At the least, we're disrupting their communication; at the worst, we're driving them bonkers," says ichthyologist Phillip Lobel.(6)
Most fish enjoy companionship and develop special relationships with each other. One South African publication documented the relationship between Blackie, a goldfish with a deformity that made it nearly impossible for him to swim, and Big Red, the larger fish who shared his tank. Big Red daily put Blackie on his back to swim him around, and when they were fed, Big Red swam Blackie to the surface, where they ate together.(7)
Fish enjoy tactile stimulation in their relationships and often gently rub against each other. Divers tell of gaining the friendship of fish by lightly scratching their foreheads—they've found that the fish then recognize and regularly approach them.(8)