Mental barbel variation in Pogonophryne scotti Regan (Pisces: Perciformes: Artedidraconidae)

Abstract

The mental barbel, an important diagnostic character among notothenioid fishes of the family Artedidraconidae, is highly variable in Pogonophryne scotti. A collection of 92 specimens of this species from the South Orkney Islands, comprising both sexes and a wide range of sizes, was studied to determine intraspecific variation in barbel size, shape and ornamentation (development of papillae and folds, especially on the tip). Four distinct barbel types, based on external morphology, are represented in this material: scotti (4.3%), phyllopogon (28.3%), dolichobranchiata (4.3%) and brainlike (38.1%). Indeterminate barbels (25.0%), observed in specimens of both sexes and all sizes, exhibit varying degrees of ornamentation and suggest that all barbel types represent the range of variability in P. scotti. There is no correlation between sex and barbel type. Barbels exhibit negative allometric growth relative to body size. Specimens of at least 119 mm SL generally exhibit greater development of the terminal expansion, resulting in a convoluted brainlike appearance previously unrecorded for P. scotti. Indeterminate and phyllopogon barbels are most common among specimens of 119–210 mm SL. All barbel types are similar histologically. A core of pseudocartilage is surrounded by connective tissue, and the entire barbel is well supplied with blood vessels and nerves. Papillae and folds are dermal projections covered by epidermis. The variation exhibited by the barbel of P. scotti. formerly served as the basis for distinguishing this species from the invalid species P. phyllopogon and P. dolichobranchiata. Such intraspecific variation is atypical for Pogonophryne but underscores the need to fully validate any taxonomic character.