Zebra fish

 Zebra fish is a model organism that is primarily used for experimental and genetic research, due to a number of key characteristics. This model organism is frequently used for developmental research due to the embryos being transparent (allows the development of the embryo to be observed) and as the zebra fish lays eggs. Therefore, the embryos are easily accessible. Other characteristics that make the zebra fish a model organism are:

- It has been genetically sequenced
- It has a developmental process similar to mammals
- It's easy to manipulate genetically
- It's easy to manipulate experimentally (physically and chemically)
- It's capable of regenerating many body parts (e.g. heart, fins)
- Relatively cheap

Reference: 
Richard Twyman (2002), Wellcome Trust, The human Genome Project - Model organisms: Fish, http://genome.wellcome.ac.uk/doc_WTD020806.html (Accessed: 24/11/2013)