How to Use the Key
Below is a sample section from the key to the fish families. The concept of a dichotomous key is pretty simple—the reader chooses from two different options to reach the next step and so on until the end, in this case the name of a fish family, an illustration of a family representative, and a page number where the family description and the species present in the Gulf of California can be found. To start, simply turn to page 10 and begin with number 1. Read each description and choose the option (a or b) which best coincides with the features of the fish in question and follow it to the next step. The order and classification of the families in the text is based on Fishes of the World (Nelson, 1994) with a few exceptions that are cited. The species therein are alphabetized by genera.
The key to the families is based primarily on qualitative (“artificial”) external morphological characters: body shape, fin position, etc. so it is not necessary to have a complete understanding of fish physiology and skeletal structures to use the key. But if you find that there is a gap in your knowledge of fish external morphology an illustrated glossary follows this page.