If you have a small flat but still want to keep fish, or your child wants some in their bedroom, a so-called “nano aquarium” might seem like the right way to go. These smaller-sized aquariums are increasingly available online and in pet shops – and yet they are entirely inappropriate for many sea creatures in the long term, according to Germany’s Association for Professional Nature, Animal and Species Conservation (BNA) points out. Nano aquariums often have an edge length of 30 to 50 centimetres and a capacity far less than 54 litres. However ornamental fish should be kept permanently in a tan…