It reaches 7–12 cm (2.8–4.7 in) length in total, females measuring roughly 1–2 cm (0.39–0.79 in) longer than males, and a body weight of 1.4–6.4 g. The tail is compressed sideways and is half as long or slightly shorter than the rest of the body. During their life in water, both sexes develop a tail fin, and males a low (up to 2.5 mm), smooth-edged crest on their back.