The model animal Danio rerio, zebrafish

Danio rerio, commonly known as zebrafish, is a small freshwater teleost belonging to the Cyprinidae family, originating from the Ganges region and currently distributed in the river habitats of India, Pakistan, Nepal, Bangladesh, and Myanmar.

 

Its name derives from its peculiar pigmentation, which normally consists of horizontal blue stripes that can extend to the caudal fin. There is also another variety that, instead of continuous lines, has blue dots on the sides of the body. For this reason, the two varieties are distinguished by the names zebra and leopard.

 

Typically, female individuals display a white-silver color, which becomes pink-orange in males, especially in the tail area. The two sexes can also be distinguished by the streamlined shape of the males and the enlarged, white-colored abdomen of the females. The average size of the fish ranges between 4 and 6 cm in length, and the females are usually larger than the males.

 

The zebrafish is now widely used as a model organism in many different disciplines, ranging from developmental biology to medical and toxicological studies.

 

The reasons for the enormous success achieved by this model organism in the scientific field are numerous:

 

• Its small size makes it easy to breed in captivity, in small tanks, with relatively low maintenance costs, especially compared to other vertebrate models.
• Its fertility is very high; females can reproduce once a week, releasing about 100-200 eggs each reproductive event.
• External fertilization allows for direct analysis of the embryo during development and enables the use of experimental genetic manipulation techniques without the need to sacrifice the mother, as is necessary with mice.
• The eggs and embryos, during the early stages of life, are completely transparent, allowing the monitoring of organ and tissue development in vivo, also thanks to the availability of transgenic lines capable of expressing fluorescent reporter proteins in specific tissues or cells. These lines also allow for the visualization of physiological processes, such as the inflammatory or immune response.
• Development is very rapid: within 24 hours, most organs are already formed, in 2/3 days the embryo hatches from the chorion, and the fish reaches sexual maturity between 3 and 4 months. Additionally, the life expectancy is about 3 years.
• It has a high genetic similarity with humans (more than 75% homologous genes). Despite anatomical differences, the main mechanisms of embryonic development, metabolism, and physiology are highly conserved, making the zebrafish a very useful tool for studying human diseases. Furthermore, the zebrafish is an ideal model for screening the effects of bioactive molecules (beneficial and/or pharmacological effects) or for screening the toxicity of new molecules.

 

In-depth information on the use of zebrafish as a model organism can be found in Choi et al., 2021, while information on the use of zebrafish for the identification of new bioactive molecules, such as those found in the muds of the Euganean Thermal District, can be found in the article by Crawford et al., 2008.