Modified Silver Impregnation as a Method for Fish Nervous Tissue Visualization

— The fishes’ nervous system is one of the key objects of evolutionary and biomedical researches. The multiple approaches and methods for visualizing the nervous tissue in fish have been developed, but all possess constraints and disadvantages reducing their application possibilities. As a result, the clear distinctive histological picture of the larval and juvenile nervous system of non-model fish remains a challenging task. Here, we present a modified silver impregnation protocol allowing analyzing the ray-finned fishes’ nervous system morphology with a clear background, including bones, cartilages, and muscles, at the early developmental stages, from embryo to juvenile. The main advantages of the protocol are (i) stable staining results; (ii) ability to stain specimens differing in the applied fixatives and storage duration; (iii) affordable relatively non-toxic chemicals; (iv) differentiation of all the major tissues.