Saltwater Aquarium Fish: A Look at the Molly Miller Blenny


PetMD Editorial

Published May 3, 2019

We all love pretty fish. Saltwater aquarists can get especially spoiled, as there is a seemingly unlimited range of bold colors and patterns amongst the reef fishes.

But, is there more to an "ornamental" fish than its pigments? Can a drab fish have very much value to an aquarist?

There certainly is one species that fits the bill—the molly miller blenny (Scartella cristata).

Adapted for Many Nearshore Habitats

Scartella cristata is very much cosmopolitan in distribution. Built to withstand the rigors of life in the shallow intertidal zone, it is established throughout many tropical, subtropical and temperate seas.

Not one to allow itself to be excluded from any sort of nearshore habitat, the species can be found in the Northwest Pacific Ocean (Japan to Taiwan), the Eastern Atlantic Ocean (from Mauritania and the Canary Islands to South Africa), the Western Atlantic Ocean (from Florida to Brazil) and the Mediterranean Ocean (from Spain to Greece). Its growing presence in Southern Europe has been attributed to the effects of global climate change.

Molly millers prefer very shallow waters where large predators are scarce and benthic algae is abundant. Densities sharply decrease with increasing depth. While they occupy small tide pools down to around 10 meters deep, population densities are greatest at 2-4 meters depth.

Recommended for Novice Aquarists

Smart, tough, fast and resourceful, the molly miller blenny is not one to be easily intimidated or outdone by its tankmates.

Indeed, they are about as hardy as a marine aquarium fish can be. Captive-bred specimens are practically bulletproof. For this reason, S. cristata can be highly recommended as one of the first fish (if not the first fish) in a novice aquarist's new setup.

Molly millers are sturdy enough to tolerate a bit of instability during the maturation process as the system becomes fully established chemically and biologically.

Small Fish, Big Personality

Under that tough exterior, however, is an unusually lively and interesting animal. There are certain types of marine fishes that tend to become bona fide pets in the eyes of their keepers, and this is one of them.

Possessing a considerable amount of personality, this active little fish can put on quite a show. Whether doing everything they can to steal a bit of marine fish food from a crab or squabbling with each other over a choice spot on a rock, molly miller blennies are not known to sit still for long.

Their small size is also a big plus to some (particularly those who operate nano aquaria). Despite the molly miller’s larger-than-life presence, it rarely exceeds 10 centimeters length.

The Ultimate Cleaner

Arguably, the most notable of its traits in the eyes of reef aquarists is its habit of eating pests and solid organic wastes.

The molly miller blenny has awesome potential as a member of your cleanup crew. It is, in fact, the first fish species to be captive-bred specially as a cleaner critter.

As an algae-eater, it presents a sustainably aquacultured alternative to wild-caught imports, such as the lawnmower blenny.

This fish will happily mop up ugly nuisance algae and biofilms that other "herbivores" turn their noses up at. Some have even reported that it consumes cyanobacteria! What's more, if hungry enough (and they are always hungry), they will also eat detritus.

They are most unusual (and useful) in their habit of eating the dreaded Aiptasia glass anemone. There remains debate regarding the extent to which the pest can be controlled by the fish (and, maybe even the exact action through which this occurs). Even so, it is pretty clear that S. cristata has a negative impact of Aiptasia.

In addition to consuming smaller individuals, the fish might also harm larger individuals by (1) repeatedly disturbing them while grazing and (2) competing with them by reducing detrital food stores.

Considering the threat that the hard-stinging Aiptasia makes against corals, it's possible that by preventing a single outbreak, a few molly millers can save a reef aquarist considerable investment.

As the fish cleans up its environs, be sure that it doesn't go hungry by supplementing its diet with a quality algae-based food such as Omega One Super Veggie Kelp Pellets.

The Molly Miller Blenny Is Multi-Functional

The molly miller blenny can best be described as a general-use utility fish. Able to tough out the sometimes harsh surroundings during the cycling period, they can be used along with other super-hardy species to condition new aquarium systems.

As different types of algal plagues rear their ugly heads, the molly miller will be there to eradicate them. They might also eat detritus as it accumulates on the tank bottom. Perhaps most importantly, it will help to control numbers of glass anemones.

You might come to love your molly miller because of their incredible usefulness and charming and entertaining antics—despite their modest hues!

By: Kenneth Wingerter

Featured Image:

Help us make PetMD better

Was this article helpful?

Get Instant Vet Help Via Chat or Video. Connect with a Vet. Chewy Health