Slender Triplefin, Enneanectes glendae

Slender Triplefin, Ennenectes glendae, Females. An exceptional portfolio of underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2022, courtesy of Ron Woheau, Zihuantanejo. Identifications courtesy of Dr. Ross Robertson, Smithsonian Institute, Panama.

Slender Triplefin, Ennenectes glendae, Males. An exceptional portfolio of underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2022, courtesy of Ron Woheau, Zihuantanejo. Identifications courtesy of Dr. Ross Robertson, Smithsonian Institute, Panama.

The Slender Triplefin, Enneanectes glendae, is a member of the Triplefin or Tripterygiidae Family, and are known in Mexico as tres aletas delgada. Its common name stems from the division of its dorsal fin into three parts, two of which have spines. Globally, there are one hundred forty-five members in the Tripterygiidae Family placed into thirty genera with ten known species in the genus Ennenectes of which eight are found in Mexican waters, three in the Atlantic and five in the Pacific Ocean.

The Slender Triplefin has a slender head and body and their head has large eyes and a short sharply pointed snout. Their head is covered with red-brown spots behind the ear; they have dark spots under the front of the eye and under the center of the eye; their body has 4 or 5 irregular brown bars. The anal fin is red-brown with a clear outer margin; their caudal base is red-brown with a black bar at the rear; their caudal fin is red-brown with a central clear base; their first dorsal fin has black spines with yellow and red-brown membranes; their  second and third dorsal fins have diagonal barring across the spines; and their pectorals fins are gray. Females are weakly barred; breeding males are almost entirely black.

The top of the head is covered with short, close-set slender spines with small narrow triangular cirrus over the eyes. Their anal fin has 19 or 20 rays; their first dorsal fin has 3 spines; their second dorsal fin has 12 to 15 spines; their third dorsal fin has 8 to 10 rays; their pectoral fins have 15 to 17 rays; and, their pelvic fins have 1 spine and 2 rays. They are covered with large rough scales. Their lateral line is straight and broken into two portions.

The Slender Triplefin is found in shallow water reef environments around rocks and boulders at depths up to 15 m (50 feet). They reach a maximum of 3.1 cm (1.2 inches) in length. They consume small invertebrates. Reproduction is oviparous with hemispherical eggs that attach themselves to the substrate via sticky threads. The larvae are planktonic. The Slender Triplefin is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Slender Triplefin can be confused with the Delicate Triplefin, Enneanectes carminalis (body covered with five bars), the Mexican Triplefin, Enneanectes macrops (top of the tail base white) and the Panama Triplefin, Axoclinus lucillae (caudal fin with wide black, red and white bars; pectoral fins with three pink bars).

The Slender Triplefin is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from along the coast of the mainland from Puerto Vallarta south to Guerrero and around Tres Maria Island.

From a conservation perspective the Slender Triplefin has not been formally evaluated. They are seldom seen by humans and are of limited interest to most.