Tripterygion melanurum is a species of threefin blennies belonging to the class Actinopteri, the order Blenniiformes and the family Tripterygiidae. It is a species found only in the Mediterranean Sea and generally associated with waters no deeper than 8-10 meters. It is a benthic species, which lives on sinuous rocky bottoms, preferably on dark places and with the presence of algae.
The body of Tripterygion melanurum is elongated (up to 4-5 cm in total length) and thin, presenting a conical and somewhat pointed head. Also prominent on its head are somewhat prominent lips and present but poorly developed supraocular appendages. Its eyes are round and relatively large for the size of the head. It has 3 distinct dorsal fins, a characteristic feature of the threefin blennies. The first dorsal fin is small in size, triangular in shape and black in color. The second dorsal fin has 14-16 spines that gradually decrease in length as they run towards the rear. Finally, the third dorsal fin is formed by 10-13 soft rays. The anal fin has 1-2 spines and 19-20 soft rays. The pectoral fins are large and their shape ends in a point. The pelvic fins are forked and the caudal fin is somewhat rounded. As for the coloration of Tripterygion melanurum, the base color is reddish, with a cephalic mask with brownish and bluish-white spots.
There are two subspecies of Tripterygion melanurum, both sharing the above description. Tripterygion melanurum minor and Tripterygion melanurum melanurum. The only differentiation between the two subspecies lies in the presence or absence of a black spot on the upper dorsal part of the caudal peduncle. While Tripterygion melanurum melanurum melanurum has such a black spot, Tripterygion melanurum minor does not.
Tripterygion melanurum is a species whose male specimens are very territorial. Those male specimens that are in breeding season intensify the coloration of their cephalic mask being much darker. Females and non-breeding males tend to have a less intense and more grayish cephalic mask. During the breeding season, the male takes a rocky territory of a few tens of centimeters, in an area protected from the waves and currents. During this time he will not stop courting as many females as pass through his territory. To these females he performs a zig-zag dance with all his fins fully deployed and at the same time making rapid movements up and down with his head. After this ritual, and after the eggs have been laid by the female and immediately fertilized by the male, it will be the latter who will take care of the eggs.
Although there are clear differences, confusion between Tripterygion melanurum (subspecies Tripterygion melanurum minor and Tripterygion melanurum melanurum), Tripterygion tripteronotum and Tripterygion delaisi (subspecies Tripterygion delaisi delaisi and Tripterygion delaisi xanthosoma) is common. To summarize, these are the main characteristics that differentiate them:
- Tripterygion melanurum minor. The spines of the second dorsal fin gradually decrease in height. Absence of black spot on the upper dorsal part of the caudal peduncle. Reddish color.
- Tripterygion melanurum melanurum. The rays of the second dorsal fin gradually decrease in height. Presence of black spot on the upper dorsal part of the caudal peduncle.
- Tripterygion tripteronotum. First spines of the second dorsal fin much longer than the following ones. Cephalic mask extends to pectoral fins. Color reddish-brown or yellowish-brown with dark bands on the flank (the last one, located on the caudal peduncle is very faint).
- Tripterygion delaisi delaisi. First spines of the second dorsal fin much longer than the following ones. Cephalic mask does not reach the pectoral fins. Absence of black spot on the upper dorsal part of the caudal peduncle. Bright yellow color without bands on the flanks or if present very faint.
- Tripterygion delaisi xanthosoma. First spines of the second dorsal fin much longer than the following ones. Cephalic mask does not reach the pectoral fins. Presence of black spot on the upper dorsal part of the caudal peduncle. Bright yellow color with dark bands on the flanks, the last of them, located on the caudal peduncle is much darker than the rest.