# Zebrafish Larval Melanophores Respond to Electromagnetic Fields Exposure
## 1 Introduction  
Living organisms are exposed to magnetic fields, the intensities of which are under the Ampere law that links magnetic intensity to current intensity. Variable magnetic fields are responsible for the generation of electric fields known as inducted fields; they differ from electrostatic fields and are explained by the Faraday law [1; 2; 3].  
Electric fields generally interact with electric charges of invested bodies, both fixed and moving, according to the Coulomb law, which determines a change on system energy. Instead, the magnetic field only interacts with moving charges, spin, and magnetic moment, applying a force on the charges according to the Lorentz law.  
Electric negative charges are tightly bound to their atoms and are responsible for the magnetic moment of the matter, biological or otherwise. The exhibited magnetic moment of the matter is regulated by quantum mechanics and is responsible for molecular ferromagnetism and para-magnetism. All matter is subjected to such phenomena. In this frame also operates diamagnetism. This--a much less evident phenomenon--is anothercharacteristic of all molecules and is sensitive to the derivative of the magnetic flux because of the Lentz law. Thus, significant effects are evident at high frequencies.  
Almost all biological matter can be considered paramagnetic, and its interaction with a magnetic field leads to a mechanical moment corresponding to the product \(\overset{\rightarrow}{N}=\overset{\rightarrow}{M}\times\overset{\rightarrow}{B}\), where \(\overset{\rightarrow}{M}\) is the matter magnetic moment and \(\overset{\rightarrow}{B}\) the external magnetic field [4]. Inside the matter, the mechanical moment can vary the orientation of the molecules, especially the less bound, and changes the energy of the molecule expressed as \(E_{\text{B}}=-\overset{\rightarrow}{M}\cdot\overset{\rightarrow}{B}\)[4]. To study the effects of fields on biological substrates is not an easy task. Generally, it is assumed that the mechanical moment induced by a magnetic field can influence the energetic state and, so, also the charge transport through the cells. Considering the magnetic moment caused by the molecule electrons only, the spin of which is \(\pm\frac{1}{2}\), the energy variation, according to Equation (1), can be positive or negative; namely:  
\[E_{\text{B}}=\pm\ g\cdot\mu_{\text{B}}\cdot B\cdot m \tag{1}\]  
where \(g\) is the factor of Lande, which is close to 2.00 for free electrons and for most organic radicals [4], \(\mu_{\text{B}}\) is the magnet of [PERSON], \(B\) is the magnetic field, and \(m\) is the quantum constant.  
On Earth, a (geo)magnetic field is present, which is relevant for living organisms, although its intensity is very low, \(\sim\)50 uT, as is its variation during the day and year. Nowadays, more intense fields operate in the environment. In laboratory experiments, they may range from a few 0.001 to 3 T.  
Previously, we studied the effects of magnetic fields on the morphology and locomotor (posture, swimming, and circling) behavior of zebrafish (_Danio rerio_), a well-recognized model from vertebrate biology to ecotoxicology (and nowadays widely used as a model also in biomedical research) in larvae at 5 days post-fertilization (dpf) [5]. Zebrafish embryos were exposed to static and four frequency fields up to 900 MHz for up to 5 days. The magnetic field intensity ranged from 240 nT to 40 mT. In this study, we extend the previous work to define the effects of the same stimuli on zebrafish body pigmentation [6], which results from the precise arrangement of three main classes of pigment cells: black melanophores, yellow xanthophores, and iridescent iridophores. Here, we emphasize the changes in the melanophores. The survival rate is also studied.