dorsal fin ray count

dorsal fin ray count
enumeration of the soft dorsal fin rays. In fishes where the smaller rays in front gradually grade into larger rays, these smaller anterior rays are included in the count, e.g. Ictaluridae, Esocidae, Gadidae. Where the first small rays abruptly change to larger ones or where the first small rays are very variable or difficult to count these are not included; the first unbranched ray reaching nearly to the tip of the fin and the remainder of the rays are then counted - this is called the principal ray count. Where the last two rays are closely approximated at the base some authors consider them as a branched ray counting them as one (although they are not really a single branched ray). In fishes where the last two rays are not closely placed at the base, the rays are usually both counted. However some authors again count the last two rays as one. In some studies, only the branched rays of the dorsal fin are counted. It may readily be seen that if published counts are to be of use to others the method of counting should be stated

Dictionary of ichthyology. 2009.

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