What sort of taxonomic characters are used for fish identification?
It depends entirely on which species you are looking at. In some cases, a step in a key might be as simple as comparing the number of rays in the dorsal fin, but at other times you could be asked to do something much more complicated, such as identify the type of dentition on the pharyngeal bone – something common when identifying certain cichlids to species level. Typical characters used in a key might be body proportions, colours, or what are known as meristic features. These traits are essentially those things that can be counted, such as the number of rays in the anal fin, scales along the lateral line or even vertebrae in the spine. Meristic stuff isn’t usually excessively complicated, but the terminology can be mind-boggling. At the most basic level, it’s concerned with the presence or absence of a feature (such as whether an adipose fin is present or not) and goes on to look at more detailed things like the number of soft branched rays in comparison to hard spinous rays. Basic f