Frequently Asked Questions
The most-asked questions about blennies.
What exactly is a blenny?
A blenny is any member of the family Blenniidae, a diverse group of small, mostly marine fish known for their large eyes, short bodies, and tendency to perch on rocks or coral rather than swimming in open water. They are found in both tropical and temperate seas around the world.
How many species of blenny are there?
Taxonomists currently recognize roughly 200 to 250 species spread across several genera, making Blenniidae one of the larger families within the order Blenniiformes. New species continue to be described, particularly from deep-water and cryptic reef habitats.
Where do blennies typically live in the wild?
They favor shallow, structured environments such as rocky intertidal zones, coral reefs, seagrass beds, and mangrove roots, usually staying close to the substrate. A few species tolerate brackish or even freshwater, but the vast majority are strictly marine.
What do blennies eat?
Most are opportunistic omnivores, grazing on microalgae, detritus, and tiny invertebrates like copepods and amphipods. A handful of larger species will also take small crustaceans or even the eggs of other fish.
Are blennies good for a home aquarium?
They are among the most recommended reef-fish choices for beginners because they are hardy, active, and generally peaceful. That said, a few species are territorial or will nip at smaller tankmates, so research by species is still important before purchasing.
What physical traits make blennies easy to spot?
They usually have a stout, eel-like body, a small terminal mouth, and notably large, high-set eyes. Many lack a functional swim bladder and instead use their broad pectoral fins to grip or 'walk' across surfaces.
How big do blennies get?
The majority stay between 5 and 15 cm (about 2–6 inches) in total length. A few larger genera, such as some species of Parablennius, can approach 25–30 cm, but truly large blennies are the exception.
What is the typical temperament of a blenny?
Most are curious and bold, often approaching the glass or the keeper's hand in an aquarium. Aggression is usually limited to same-species or same-diet competitors; mixed-species community tanks work well when compatible species are chosen.
How long do blennies live?
In the wild, most species reach 2 to 5 years, though some larger or slower-growing species have been recorded living past seven. In well-maintained aquariums with stable water parameters, they commonly reach the upper end of their natural lifespan.
What is a surprising or notable fact about blennies?
Several species are protandrous hermaphrodites, meaning they are born male and can later change to female if a dominant male is absent. Additionally, some intertidal blennies can leave the water for short periods, breathing through their moist gill chambers and moving across rock surfaces using their pectoral fins.