Blennies, from the suborder Blennioidei, are a large group of marine fish that includes six families and 833 species. They are a popular fish among aquarists, although only a few of these species are recommended for aquariums. They are colorful, typically friendly to other species, reef safe, and can be beneficial to your tanks ecosystem. In this article, we are going to look at the characteristics, tank conditions and diets of these beautiful marine species.


The suborder Blennioidei is a very diverse group of fish. Blennies typically have large mouths and eyes relative to their small elongated, tapering bodies. Their blunt head and snout contains several appendages called cirri that can be either smooth or multi-branched. The function of these cirri is unknown. The pelvic fins of blennies are also very close to their gills and their caudal fin is rounded. In the wild, they are typically bottom or reef dwellers and live in temperate to warm waters. They are also known to live around eelgrass or in kelp beds. Some species can even be found in fresh or brackish water. Most blennies do not have a functional jaw or teeth and are omnivores, with the exception of the clinids and a few others species which are generally carnivorous. Sometimes confused with gobies, blennies have a singular dorsal fin as opposed to gobies which have two dorsal fins.

Tank Conditions

Due to the diversity of this group, it’s impractical to generalize on the tank conditions that all blennies require. Water quality parameters should be discussed with an aquarium professional before stocking them in order to ensure that the tanks conditions are suitable for that species. One common trait among blennies is their territorial nature. Although they are unlikely to harm another fish, they will protect their territory. It is recommended to give them plenty of hiding places such as the rockwork of reefs or aquatic plants. Some blennies, such as the Lawnmower Blenny, can help manage the green algae in your aquarium to keep it looking presentable.

Fish Diet

Blennies are generally omnivores but most tend to feed more on vegetative matter. It is important to give them a varied diet in order to keep them healthy. Prepared flake or pellet feeds with protein, mysis shrimp, spirulina pellets, and nori are all possible feeds for blennies but be sure to change them up.

The Takeaway

Although they can vary a lot both physically and environmentally between species, blennies can make a great addition to many aquariums. Their friendly nature and unique physical characteristics make them an interesting fish that can help add diversity to your tank.

-Richard Bryant
contributor for Aquarium Network