The violet goby, Gobioides broussonnetii, is a member of the family Gobiidae of the order Perciformes

Perciformes

The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...

. It is native to brackish waters near the Atlantic coast of North and South America. Its commercial trade name is Dragon Goby or Dragon Fish. It is often sold as a "highly aggressive" fish, but violet gobies are actually quite docile, and nearly blind.

Distribution

Violet gobies are found all along the Atlantic coast from Georgia

Georgia (U.S. state)

Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...

 in the United States of America, to northern Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

.

Description

The Violet goby has a long, slender, eel-like body. Its dorsal and anal fins run almost the entire length of the body. The teeth are very sharp; however these are used for scraping algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 off rocks, not fighting. When kept in good condition, dragon gobies develop an attractive, iridescent, silvery-blue metallic color with a gold blotch pattern. Violet gobies seen in pet stores are generally 3 to 5 in (7.6 to 12.7 cm) long. In the wild, violet gobies can grow to 24 inches (61 cm) long. However, in captivity they seldom grow past 15 inches (38.1 cm). No external differences between the sexes are known, although males are more territorial at spawning times.

Habitat and feeding

Violet gobies usually inhabit brackish swamps, streams, and estuaries with a muddy substrate. Violet gobies have very small eyes, and as such are primarily scavengers. Their key method of obtaining food is by scooping up mouthfuls of gravel and sorting edible material from the substrate, and then spitting out the substrate and swallowing the food particles. They also use their highly specialized teeth to scrape algae off of rocks.

Popularity, availability, and hardiness

This is not a very common fish among hobbyists, perhaps because it is hard to find, both commercially and in the tank. Dragon gobies tend to disappear from the market for long periods of time, but are easier to find in stores within their natural range. Meanwhile, they often hide all day, coming out only when the lights are out and owners asleep. As noted above, they are often described by Local Fish Stores as aggressive, capable of eating any fish that fits in their mouth...when, in fact, they are simply detritivores.

Behaviour and aggression in captivity

Despite its fierce looks, large mouth, and many teeth, the violet goby is a predator scavenger. If well fed, it usually will not bother smaller fish. Any small, peaceful, brackish water-tolerant fish can coexist with violet gobies. Examples include mollies, guppies

Guppy

The guppy , also known as the millionfish, is one of the most popular freshwater aquarium fish species in the world. It is a small member of the Poeciliidae family [females long, males long] and like all other members of the family, is live-bearing....

, swordtails, platies, bumblebee goby, and glass fish. The violet goby is only kept with peaceful fish, as it has poor eyesight and may be bullied by more boisterous fish.
However, if two violet gobies exist in a tank too small, one will eventually claim the entire area their own territory and fiercely defend it.

Temperature, pH, and salinity

Violet gobies are generally healthy at temperatures between 76-78°F (24-26°C), with a pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 between 6.5–8.5, and salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 at 1.006–1.008.

Feeding

Violet gobies are scavengers in the wild and need a varied diet for optimum health, but are limited by two factors, their small throat size and very poor vision. Despite having huge tooth-filled mouths, these fish actually have very small throats and this limits the kinds of foods they eat. They eat both animal and plant-based foods, such as frozen blood worms, frozen tubifex worms, baby brine shrimp, and vegetable flakes. Unless they are in a species specific tank, violet gobies cannot compete with other fish to find food, because of poor eyesight. Violet gobies often feed at night.

Breeding

They typically spawn in a group of one male and three or more females. Females require many hiding places, while the male needs a site to build his nest. Spawning is triggered by feeding on live meaty foods, and a decrease in salinity from 7 parts per thousand (1.006–1.008sg) to around 5 parts per thousand (1.004), followed by an increase to 30 parts per thousand (close to regular marine salinity, about 1.023sg). The male spawns with several females over the course of a day. After spawning, the male guards the eggs. After 1.5–2 days, the eggs hatch. Fry eat infusoria

Infusoria

Infusoria is a collective term for minute aquatic creatures like ciliates, euglenoids, protozoa, and unicellular algae that exist in freshwater ponds...

 (particularly rotifer

Rotifer

The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...

s) and "green water" (single celled algae) for up to a month. They then eat baby brine shrimp

Brine shrimp

Artemia is a genus of aquatic crustaceans known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period...

 nauplii.

Diseases

Dragon gobies are susceptible to many common aquarium illnesses, such as Columnaris

Columnaris

Columnaris is a symptom of disease in fish which results from an infection caused by the gram negative, aerobic, rod shaped bacterium Flavobacterium columnare. It was previously known by the names of bacillus columnaris, chondrococcus columnaris, cytophaga columnaris and flexibacter columnaris...

and fin rot

Fin rot

Fin rot is a symptom of disease or the actual disease in fish. This is a disease which is most often observed in aquaria and aquaculture, but can also occur in natural populations....

; which are bacterial infections that spread across the skin and fins of the fish. They are usually treated with antibacterial

Antiseptic

Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

 or antibiotic

Antibiotic

An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

medications.