Sooner or later, the serious marine aquarist cannot fail to come upon these endlessly fascinating and endearing group of fishes. Their curious habits and occasional brightly coloured appearance have continued to make them a firm favourite with reef and fish-only keepers alike.
Blennies are found in seas all over the world. They are particularly abundant in tropical, sub-tropical and temperate waters. Indeed, there are over 300 species included in the family Blennidae alone, with another 400 in closely associated genera. The largest rarely exceed 10cm in length and are therefore ideally suited for life in the aquarium. Newcomers will find the majority of specimens an ideal first choice and many can be recommended without hesitation.
Although it is not of great importance to the average hobbyist, blennies and gobies are often confused as they share many similar characteristics. For example, many members of both families are bottom-dwellers and tend to occupy a cave or burrow for protection. However, they are easily distinguished as the pelvic fins of the gobies are fused together to form a sucker-like disc, enabling them to ‘perch’ on vertical, or even overhanging surfaces. Whilst blennies are also versatile, their pelvic fins are distinctly separate and they tend to rest on horizontal surfaces where they can get a good view of the surrounding area. Making full use of their ability to move each eye independently, predators are soon spotted and the fish can quickly retire to the safety of its chosen burrow or crevice. But there are exceptions in all things and to this type of behaviour. For instance, the Scooter Blenny (Petroscirtes temmincki) has no burrow, it merely freezes when threatened and relies on its highly camouflaged body for protection. On more macabre note, the Sabre-Toothed Blenny (Aspidontus taeniatus) is a free-swimming species that mimics the coloration of the common Cleaner Wrasse (Labroides dimidiatus). Unlike the Cleaner Wrasse, the Sabre-Toothed Blenny has far from friendly intentions! No sooner has it gained the confidence of another fish fully expecting to be cleaned of parasites, than it tears off a piece of flesh instead! Obviously, this does not make a good introduction to the marine aquarium if tankmates are to remain in good condition! Fortunately, the Sabre-Toothed Blenny is reasonably easy to distinguish from the true Cleaner Wrasse because it has a distinctly shark-like underslung mouth and is generally not quite as brightly coloured as the true Cleaner Wrasse.
Being such a large family of fish, feeding methods vary widely from substrate browsers, algae eaters, plankton feeders and flesh eaters as we have seen. However, by far the largest group are the plankton feeders who tend to perch on a convenient outcrop and dart out to grab any tasty morsel that happens to drift by carried in the current. In the aquarium, blennies have very catholic tastes and will readily take frozen or live brineshrimp as well as other finely chopped pieces of marine fare. Most species will also eagerly take marine flake.
Most blennies spawn in a cave or burrow. The males generally take the responsibility of guarding the eggs until they hatch. The newly hatched larvae subsequently make their way to the surface plankton layers to feed until they are mature enough to descend to the sea floor. It is possible to positively sex a number of species and these will quite often pair-up and spawn in the aquarium. Eggs are frequently laid in barnacle shells and guarded by the male. Unfortunately, the larvae are extremely difficult to rear in captivity, even though for some time professional breeders have been trying.
Blennies are largely territorial by nature and are loathe to tolerate the same, or similar, species in the same aquarium (excluding where true pairs have been identified). There are, of course, exceptions here but a mixture of blennies in the same aquarium is not a guaranteed recipe for success. Unrelated families are nearly always ignored and although they are inquisitive fish, blennies invariably get on well with species that present no threat to them.
It is essential that the blenny be made to feel at home by providing plenty of rockwork, built up into high points where the fish can perch and observe the scene. Large barnacles are appreciated as convenient retreats during the day and nightime. Sparsely decorated aquaria should be avoided as they will tend to stress the fish.
The vast majority of blennies are entirely compatible with both mobile and sessile invertebrates. They are highly disease resistant and substrate browsers often keep potential plagues of amphipods and copepods under control. Some species even graze on hair algae, although they rarely provide an efficient solution to that particular marine aquarium bug-bear.
An aquaria of 36″x12″x15″ or larger are satisfactory.
Regular water changes of about 15-20% every two weeks are essential to good health. Vigorous water circulation is also appreciated. Protein skimming and activated carbon should be seen as standard. Lighting is largely unimportant as blennies will adapt to almost any scenario, whether it be an intensely lit invertebrate tank or a moderately illuminated fish-only set-up
Blennies are not prone to any particular diseases common to the marine aquarium. However, they are intolerant of poor water conditions and will soon succumb as a response to bad husbandry.
Scooter Blenny (Petroscirtes temmincki)
© Nick Dakin. May not be reproduced in part, or whole, without permission.