By Monica Weinheimer
Diversity
Tripterygiids (triplefin blennies) are one of the least-studied blennies, but they are known to be cryptic, territorial reef dwellers identifiable by their three distinct dorsal fins and 
ctenoid (rough-edged) scales. There are some undescribed forms among the Tripterygiidae, but there are thought to be at least 20 genera and 150 species in the family. (Allen and Robertson, 1994; Böhlke and Chaplin, 1994; Helfman, Collete, and Facey, 1997; Nelson, 1994; Springer, 1998; Thresher, 1984; Wheeler, 1985)
Geographic Range
Triplefin blennies are found in the Atlantic, Pacific, and Indian Oceans, and one species has been identified in the Antarctic Peninsula. There are five species known to be from the Bahamas, all of which are located in the Bahamas. Blennies are generally not found on most of the Atlantic coasts of Africa and South America. New Zealand is thought to be the area with greatest diversity of triplefin blennies. (Böhlke and Chaplin, 1994; Nelson, 1994; Springer, 1998)
Biogeographic Regions:
indian ocean (native ); atlantic ocean (native ); pacific ocean (native ).
Habitat
Primarily benthic reef-dwellers in tropical and warm temperate seas, triplefin blennies commonly live near reef surfaces, rocky slopes, rubble, or algae-covered rocks. Depth and habitat can vary according to specific local adaptations. One species can sometimes be found in estuaries. (Allen and Robertson, 1994; Böhlke and Chaplin, 1994; Graham, 1997; Nelson, 1994; Springer, 1998; Thresher, 1984; Wheeler, 1985)
These animals are found in the following types of habitat:
tropical ; saltwater or marine .
Aquatic Biomes:
benthic ; reef ; brackish water .
Other:
estuarine ; intertidal or littoral .
Systematic and Taxonomic History
There are some undescribed forms among the Tripterygiidae (triplefin blennies), but there are thought to be at least 20 genera and 150 species in the family. They are sometimes included in the Clinidae family, to which they are similar. Triplefin blennies, however, as the name suggests, can be distinguished by their three dorsal fins, the first two composed of spines and the third composed of soft rays. The only other fish with three distinct dorsal fins are hakes and cods. Triplefin blennies are also unique among blennies in that they possess ctenoid (rough-edged) scales (except for three species). (Allen and Robertson, 1994; Böhlke and Chaplin, 1994; Helfman, Collete, and Facey, 1997; Springer, 1998; Thresher, 1984; Wheeler, 1985)
Physical Description
Triplefin blennies are cryptically colored or transparent, heavily scaled, and small. Most are only 3-4 cm, the largest reaching 25 cm. In triplefin blennies the dorsal fin is divided into three distinct parts. The first two segments are composed of numerous slender spines, and the third segment is made up of at least seven soft rays. There are between zero and two anal fin spines. Scales are usually, but not universally, ctenoid (rough-edged or toothed). The nape lacks cirri, and the first gill arch attaches to the operculum, the latter characteristic distinguishing Tripterygiidae from Clinidae. Sexual dimorphism is common, with males assuming black or red coloration on the head, body, or caudal fin during spawning. Urogenital (involving both the urinary and genital structures) morphology may also differ between males and females. Gray and brown are typical colors on females and nonspawning males. (Click here to see a fish diagram). (Allen and Robertson, 1994; Böhlke and Chaplin, 1994; Nelson, 1994; Springer, 1998; Thresher, 1984; Wheeler, 1985)
Some key physical features:
ectothermic ; bilateral symmetry .
Sexual dimorphism: male more colorful, sexes shaped differently.
Development
Sticky threads anchor the eggs of triplefin blennies to algae in the nest site. After hatching, larvae in species of Tripterygion settle after approximately 40 days. One study indicates that larvae are affected by auditory cues (reef sounds) in determining where to settle. (Myrberg and Fuiman, 2002; Thresher, 1984)
Reproduction
Male triplefin blennies establish territories on rocks covered with algae. From this vantage point they signal to passing females by “loop-swimming,” a courtship motion that varies from species to species, but entails quickly hopping up and down in a loop. Males of species in Axoclinus pose before loop-swimming, resting on their pelvic fins and waving the caudal fin, which gives the female a better chance to view his courtship colors. One male may spawn with several females. (Thresher, 1984)
Mating systems:
polygynous .
Definitive information about spawning seasons of triplefin blennies is lacking, but spawning likely occurs year-round in the tropics and during warmer seasons in temperate areas. In order to spawn the male first cleans the algal filaments at the nest site, and then attracts one or more females to the nest. Spawning can last up to several hours. Eggs are deposited by the female one at a time and fertilized simultaneously by the male, with clutch sizes sometimes reaching 500 eggs. “Streaking” occurs in some species of Tripterygion and Axoclinus: smaller, most likely younger, cryptically-colored males rush in while the dominant male is engaged in spawning, releasing their own sperm in an attempt to fertilize some of the eggs. (Thresher, 1984)
Key reproductive features:
iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (external ); oviparous .
Male triplefin blennies remain near the eggs to guard them until they hatch. (Thresher, 1984)
Lifespan/Longevity
No information was found regarding the lifespan of Tripterygiidae.
Behavior
Most recorded behavior of triplefin blennies has to do with their reproductive habits (see Reproduction: Mating Systems and General Behavior). Otherwise, they frequent hidden, shadowy areas, darting to and fro with intermittent pauses. One species, Helcogramma medium, can crawl out of low-oxygen tidepools to breathe air, although it does not have a specialized air-breathing organ. (Graham, 1997; Wheeler, 1985)
Key behaviors:
natatorial ; motile ; territorial ; social .
Communication and Perception
No information was found on communication in Tripterygiidae, except regarding courtship displays by males (see Reproduction: Mating Systems).
Food Habits
Triplefin blennies feed on algae and tiny invertebrates. (Allen and Robertson, 1994)
Primary Diet:
carnivore (eats non-insect arthropods); herbivore ; omnivore ; planktivore .
Predation
Triplefin blennies avoid predators by attempting to remain unnoticed. They are small, occupy hiding places in the reef, and are cryptically colored or partially transparent. (Allen and Robertson, 1994; Thresher, 1984)
Anti-predator adaptations::
cryptic .
Ecosystem Roles
Triplefin blennies have in many cases adapted to specialized local conditions, so they may occupy otherwise unfilled roles in certain areas. They feed on and thereby impact populations of small invertebrates, and likewise may affect algal growth. (Allen and Robertson, 1994; Wheeler, 1985)
Economic Importance for Humans: Negative
No specific information was found concerning any negative impacts to humans.
Economic Importance for Humans: Positive
Some triplefin blennies are kept in aquaria, but none are considered sport or food fishes. (Wheeler, 1985)
Ways that people benefit from these animals:
pet trade .
Conservation
Currently, there is no known conservation threat to any member of this family. (The World Conservation Union, 2002)
Contributors
Monica Weinheimer (author), Animal Diversity Web.
