ABSTRACT
Many investigations on chromosomes have helped to solve taxonomic issues, elucidate meiotic behaviors, and even provided information regarding the evolution of repetitive DNA sequences, such as satellite DNAs and transpo-sons. This chapter presents an updated fish- fluorescence in situ hybridization (FISH) protocol, in which the author show a figure-guided protocol for the whole procedure and discusses some minor adaptations made over the years, such as adjustments for a sequential FISH and problems that have usually emerged using an overabundance of labeled probes. Mitotic chromosomes can be obtained by the classical air-drying method, which consists of the application of colchicine to stop chromosomes in metaphase, followed by hypotonization of cells and fixation in Carnoy 2. The chromosomal localization of ribosomal genes is an important tool for the comprehension of the evolutionary process on fishes. More recently, genomics has become an important mechanism for probes obtainment in fish cytogenetics.
