Praise be to Allaah.  

There is nothing wrong with keeping animals for which there is no Islamic prohibition on keeping them (such as dogs and pigs). There are reports in the Sunnah which indicate that some of the Sahaabah kept permissible animals for farming purposes or for fun and for pleasure. 

It was narrated from Anas (may Allaah be pleased with him) that he had a young brother who had a nughar (a small bird or nightingale). The bird died, and the Prophet (peace and blessings of Allaah be upon him) saw him looking sad and grieved, so he joked with him, and said to him words which implied approval of his keeping this bird. The Prophet (peace and blessings of Allaah be upon him) said to him, “O Abu Umayr, what happened to the nughayr?” 

And the Prophet (peace and blessings of Allaah be upon him) told us that a woman entered Hell because of a cat “which she did not feed, neither did she let it eat from the vermin of the earth.” From this it may be understood that if she had fed it, she would have been saved from that threat. 

And it was said that Abu Hurayrah was so called because of a cat (hirr, dim. hurayrah) which used to accompany him. 

So keeping permissible animals, so long as you do not neglect them, is something which is permitted and it may even be one of the means of earning reward, as the Prophet (peace and blessings of Allaah be upon him) said, “In every living being there is reward.” But if you keep animals and neglect and abuse them, it may be one of the means that lead to sin and the threat of Hell, as in the hadeeth about the woman who neglected her cat until it died. 

We would also like to point out that Islam preceded both western and eastern organizations in proclaiming the rights of women, animals, workers, employers and so on. Indeed, the greatest rights which it proclaimed are the rights of Allaah over His creation and the rights of people over Allaah. 

We would also point out that care and concern for human beings should take precedence over the care of animals, and that the reward for that is greater. [The Prophet (peace and blessings of Allaah be upon him) said:] “Ward off the Fire even with half a date [i.e., by giving half a date in charity]” and “I and the one who sponsors an orphan will be like these two in Paradise” – and he gestured with his index finger and the one next to it. And there are other similar ahaadeeth from the Prophet (peace and blessings of Allaah be upon him). 

On this basis, there is nothing wrong with your keeping fish as you mentioned in your question, so long as you take care of feeding them and avoiding anything that could cause their death. And Allaah knows best. 

With regard to the creation of dogs, Allaah created them as He created all other animals; it is not permissible to claim that dogs were created from any specific substance without having evidence for that. Allaah says (interpretation of the meaning): 

“and we testify not except according to what we know”[Yoosuf 12:81] 

With regard to Iblees, Allaah commanded him to prostrate to Adam and he refused and was arrogant, then what he did was to tempt Adam to eat from the tree from which he had been forbidden to eat. There was no kind of dirt, and Allaah knows best. I do not know anything of the argument which you mentioned. 

One aspect of the Qur’aanic guidance is that it mentioned the knowledge which the Muslim needs in this world and in the Hereafter; with regard to knowledge for which there is no need, the Qur’aan does not mention it, so as to teach the Muslims to focus on beneficial knowledge and to ignore everything else. For example, the Qur’aanic text does not mention the colour of the dog which belonged to the People of the Cave, or the kind of wood from which the ship (ark) of Nooh was built, and other matters which are irrelevant and produce no beneficial knowledge or belief. Perhaps speaking of the substance from which dogs were created comes under the same heading. And Allaah knows best.