By Scott W. Michael
Last month we began discussing what "live sand" is, what the advantages of having it in your aquarium are and how it can be "maintained" by employing fishes that help agitate the sand's surface. We will begin this month's column with a continuation of the fish species that are substrate disturbers.
Although members of the genera Istigobius and Valenciennea, and certain gobies in the genus Amblygobius, are superior substrate displacers, the shrimp gobies (e.g., Ctenogobiops, Cryptocentrus and Amblyeleotris species) also will occasionally take mouthfuls of sediment and spit it out or filter it through their gills. However, most of the shrimp gobies do not feed in this manner and are better classified as secondary substrate displacers.
Other secondary substrate displacers include those wrasses (Family Labridae) that use their heads to throw the sand to one side when searching for food or that bury in the substrate, jawfishes (Family Opistognathidae), which build burrows in the substrate, and flatfishes (Families Bothidae, Pleuronectidae and Soleidae), which bury under the sand surface and hunt prey in the sand bed. Snake eels (Ophichthidae), although unsuitable for an aquarium filled with live rock, also dig under and turn over the substrate.
Goatfishes (Family Mullidae) are primary displacers and are particularly effective if your have lots of rubble in your substrate. These fish use their sensitive chin barbels to probe the sand and flip over pieces of rubble in search of food. Some drawbacks to keeping goatfishes in the reef tank include the possibility they will eat ornamental shrimp, some species will eat small fishes, and they will quickly decimate invertebrate populations living in the exposed portions of the sand bed. Some larger goatfishes may also succeed in turning over pieces of live coral during their foraging activities.
Riseley, R. A. 1971. Tropical Marine Aquaria; The Natural System. George Allen — Unwin Ltd, London. Pp. 187.
Tullock, J. 1997. Natural Reef Aquariums. Microcosm, Shelburne, Vermont. Pp. 336.
The threadfin breams and spinecheeks (Family Nemipteridae) are also primary displacers. They feed by taking in mouthfuls of sand, sorting out the edible materials and spitting out the rest. Another group that employs a similar feeding behavior, but that are not particularly colorful, are the mojarras (Family Gerridae). These fishes are typically silver overall and live over open sand bottoms adjacent to coral reefs.
Another primary displacer is the convict worm goby (Pholidichthys leucotaenia). This species is an industrious burrower that will dig tunnels under and around your live rock. It is great for stirring up debris that has formed in places that are often hard for other displacers to get to. The drawback with this species is that its excessive burrowing can destabilize aquarium décor and cause it to topple.
Fishes are not the only organisms that engage in disturbing sand and mud substrates. There are also invertebrates that can be employed as clean-up crew. Some of the best species are crustaceans. For example, the pistol shrimp (Alpheidae) are nocturnal crustaceans that use their claws to turn over sand near their burrow entrance. These shrimp are very effective at turning the sand over, but usually restrict their activities to certain portions of the tank. There are also numerous hermit crabs that can be employed to keep the sand surface free of cyanobacteria, diatoms and filamentous algae. It is best to select smaller species, as larger forms can be quite destructive.
Some sea cucumbers bury and burrow through the sand and feed on detritus. Most of these are drably colored species that belong to the genus Holothuria. You should avoid the "medusa worms," which are a type of sea cucumber, the sea apples (genus Pseudocolochirus) and the spotted sea cucumber (Bohadschia argus). These species can poison a tank and kill all of its fish inhabitants.
There is a species of sea star (apparently in the genus Astropecton), commonly sold as sand-siting starfish, that moves on and buries in the substrate. Although it effectively agitates the sand, it is an efficient predator that will feed on many of the beneficial bivalves, crustaceans and worms living in the sand bed.
Serpent and brittle stars are also great scavengers whose activities will help to keep sediment from accumulating in and on the substrate. This is another great thing about live sand. If you keep fish and invertebrates that help you maintain it, it is usually not necessary to siphon debris off the bottom of your aquarium!
Books About Venomous Fishes
Q. In your response to a letter regarding venomous fishes (June 1998) you said "there are no books that are dedicated to these fishes..." This is not true. I have owned Poisonous Marine Animals by Findlay Russell for at least 20 years, and amazon.com on the Internet lists 16 more books on poisonous and venomous marine animals and fishes. Most of these books discuss the animals you mentioned in your article, as well as dozens more. Just thought you'd like to know that there are lots of other aquarists out there interested in these animals.
A. Well, you are correct. There are loads of books that deal with venomous and poisonous fishes. What I was attempting to communicate is that there are no books that are dedicated to the behavioral ecology and husbandry of these fishes (which was the subject matter of my reply).
Take the book you mentioned by Russell (Poisonous Marine Animals). Each chapter is dedicated to a phylum, or in the case of fishes, it is broken down into Poisonous Fishes and Venomous Fishes. In each of these chapters he discusses things like the venom apparatus, the chemistry and toxicology of the venom and clinical problems, but there is no information on the husbandry of the few fish families mentioned, and little in the way of ecological or behavioral information that would be of interest to aquarists. This not only applies to Russell's book, but also to the dozens of books on venomous fishes that I own or have seen (including Bruce Halstead's opus on the subject).