Tripterygion delaisi is a species of threefin blennies belonging to the class Actinopteri, the order Blenniiformes and the family Tripterygiidae. It is a species found both in the Mediterranean Sea and in the eastern Atlantic Ocean, from the coasts of England to the waters of Senegal. Generally associated with waters no deeper than 10-14 meters. It is a benthic species, which lives on the sinuous rocky bottoms, preferably on somewhat dark places and with the presence of algae.
The body of Tripterygion delaisi is elongated (up to 9 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 16-18 spines, the first spines being much longer, giving this second dorsal fin the appearance of a sail. This feature is much more pronounced in males than in females. The third dorsal fin is formed by 11 to 14 soft rays. The anal fin has 3 spines and 24-28 soft rays. The pectoral fins are large and their shape ends in a pointing shape. The pelvic fins are forked and the caudal fin is somewhat rounded. As for the coloration of Tripterygion delaisi, the base color is bright yellow, with a dark purple cephalic mask that does not reach the pectoral fins. There is a clear sexual dimorphism in Tripterygion delaisi, males of reproductive age, during the months of May to August intensify the black color of the cephalic mask. In contrast, females and non-breeding males have less intense colors.
There are two subspecies of Tripterygion delaisi , on the one hand Tripterygion delaisi delaisi, which does not present bands on the flanks of its body or if they do they are very little apparent. It is also characterized by not having a dark spot on the caudal peduncle. The second subspecies, Tripterygion delaisi xanthosoma does show dark bands on the flanks of its body, the last one being much darker than the previous ones. Additionally, they also have a spot on the caudal peduncle, and this subspecies has a more limited geographical distribution, being endemic to the Mediterranean Sea.
Tripterygion delaisi is a species whose male specimens are very territorial. Those male specimens that are in the reproductive season intensify the coloration of their cephalic mask being much darker. Females and non-breeding males, the cephalic mask tends to be of a less intense and more grayish color. 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 male who will take care of the eggs.
Although there are clear differences, confusion between Tripterygion delaisi (subspecies Tripterygion delaisi delaisi and Tripterygion delaisi xanthosoma), Tripterygion melanurum (subspecies Tripterygion melanurum minor and Tripterygion melanurum melanurum) and Tripterygion tripteronotum 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 spines 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.