Chitosan is increasingly used for safe drug and nucleic acid delivery due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve solubility and stability of chitosan-nucleic acid polyplexes, and enhance efficient target cell drug delivery, cell uptake, intracellular endosomal escape, unpacking and nuclear import of expression plasmids. This review focus attention on recent advances in chitosan-mediated gene delivery for fish biotechnology applications such as fish vaccination against bacterial and viral infection, control of gonadal development, and gene overexpression and silencing for overcoming metabolic limitations such as dependence on protein-rich diets and low glucose tolerance of farmed fish.