Few genetic conservation studies carried out in Colombia have applied molecular biology techniques. Protocols and modifications arising from the genetic study of four fish species from the Sinu river basin are presented as guidelines for future work in this field (and with other species) as laboratory standardisation processes are complex. The original commercial kit's DNA extraction protocols were modified as were those for PCR reactions for obtaining micro-satellite markers and AFLPs, as well as allele genotypification. Particular variations were made f or each of the species studied. Key words: DNA extraction; molecular biology; genotypification; ichthyology.