Tom & Miguel, if you take a closer look at the numbers in that study I think that you'll find that both the size of the tank, and the total number of fish, would play a large part as to whether structure & territorial boundries will or will not be successful in each set up. This is where hands on experience comes into play. An experienced fish keeper should be able to tell what's going on in their tank with regards to overall aggression & stress levels. A young kid just starting out with his first monster tank, and monster fish, might easily miss the signals. Ths is where education comes into play, and in some cases, a swift kick in the arse if neccessary. I have little patience for idiots, which clearly I do not hide well when conversing online.
Speaking of laws (Monsterminis), and things being annoying (Miguel)- I hate legislation as much as the next person, but for those that aren't aware of it not every country feels the same way (as the USA) about their animal welfare, including pets.
In Germany and Austria, the keeping of fish in tanks of less than 5 litres (14 gallons) is prohibited. Special exceptions exist only for breeding purposes and for very small species. I believe that bare bottom tanks are also prohibited.
Harro Hieronimus, chair of the German Livebearer Society and the International Rainbowfish Association, was asked to create for the German Ministry of Agriculture a set of minimum requirements for the humane care of fish. His expert opinion has been translated into law in Germany. He maintains that fish must have a minimum volume of 14 gallons of water in an aquarium approximately 24 inches by 12 inches by 12 inches in size.
Hieronimus states, "Keeping fish permanently in smaller tanks is cruelty against animals and [in Germany] may be prosecuted by law."
In the UK the Animal Welfare Act passed in 2006 introduced legislation for pet owners – giving them a legal duty of care to meet the five welfare needs of their pets.
1) somewhere suitable to live
2) a proper diet, including fresh water
3) the ability to express normal behaviour
4) for any need to be housed with, or apart from, other animals
5) protection from, and treatment of, illness and injury.
Anyone who is cruel to an animal, or does not provide for its welfare needs, may be banned from owning animals, fined up to £20,000 and/or sent to prison.
The law also increases to 16 the minimum age at which a person can buy an animal, including tropical fish.
(see below)
“Great-grandmother given an electronic tag and curfew for selling a goldfish to a 14 year-old”
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Joan Higgins, a pet shop owner, was caught selling the fish to the teenager in a ‘sting’ operation by council officials. She was then prosecuted in an eight month court process estimated to have cost the taxpayer more than £20,000.
Under new animal welfare laws, passed in 2006, it is it illegal to sell goldfish to under 16s. Offenders can be punished with up to 12 months in prison.
Mrs Higgins, 66, who thought the boy was much older than 14, escaped jail but was instead ordered to wear an electronic tag and given a night time curfew. She was also fined £1,000 by Trafford Magistrates Court. … [Her son] said the punishment she had received would prevent her from attending her weekly bingo sessions as well babysitting her one month-old great grandchild.
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It's a slippery slope ............
Full text to the article on tank size & aggression in Midas cichlids can be found in the following link.
http://www.tandfonline.com/doi/pdf/10.1080/10888705.2011.600664