News / Species Spotlight / Firefish (10/23/14)

Firefish


by Charles J. Hanley III

Scientific Name: Nemateleotris magnifica, N. decora, and N. helfrichi
Common Name: Firefish, Fire Dartfish, Decorated Dartfish, Helfrichs Dartfish

Taxonomy:

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Ptereleotridae
Genus: Nemateleotris
Species: Nemateleotris magnifica, N. decora, and N. helfrichi

Description:

One of the most standard fish in the saltwater hobby is the firefish, or fire dartfish (Nemateleotris magnifica). This fish is popular because it is beautiful, peaceful, and hardy. Though they can move quickly when they have the need, they often spend time suspended in the water column, presenting their fantastic colors for all to see. Two lesser known species, N. decora, the decorated dartfish, and N. helfrichi, Helfrichs dartfish, are similar in hardiness and rival the firefish in looks. These three species represent the entirety of the genus Nemateleotris, and I will be briefly covering all of them in this edition of Species Spotlight.

While searching for the right words to describe the way a dartfish looks, the sudden realization that dartfish look like darts hit me. You have to squint your eyes and use a bit of imagination, but they do. Firefish and the other nemateleotrids rarely exceed 4 inches. They are elongate cigar-shaped fishes that are also called wormfish, since they are much longer than they are tall or wide. Of the dartfishes, firefish (N. magnifica) are probably the most reminiscent of a dart. Their rounded caudal fins marked with angled black lines really give the impression of a darts parabolically-shaped fletching.

They have two dorsal fins, and a matching anal fin that can be comparable in size to the largest of the dorsal fins. Their caudal fins are rounded or truncate. At the anterior end of their small heads, nemateleotrids have fairly oblique mouths. This means that the lower jaw extends out further than the upper. In all species, the first dorsal fin ray is modified into a pronounced spine. In firefish, this spine can be as long as two-thirds of the total body length. Overall, Nemateleotris dartfish are morphologically similar to other dartfish, with the marked exception of the first fin ray spine that is unique to this genus.


Ecology:

Firefish are often mistakenly called gobies though there are not in the family Gobiidae at all, belonging instead to the family Pteroleotridae. The mistake is understandable, since both families have cigar shaped bodies, blunt heads, and oblique mouths. However, gobies are a diverse group that contains as many 500 species. The same cannot be said for the family Ptereleotridae, which boasts barely one-tenth that number. Moreover, the accepted taxonomy of these fish has changed over time to reflect the addition of genetic data into the overall phylogenetic picture.

The real problem is that taxonomy is quantized; that is it expresses genetic relationships in terms of discrete identifications. Organisms are categorized into exclusive groups and subgroups. Nature is rarely that compartmental, however, and taxonomic groups are encumbered by phylogenetic and cladistic characterizations. Gobies and their like are particularly confusing because their historic ancestors were once a more diverse grouping of fish species that underwent reductive evolution. Therefore, gobies, blennies, dartfish and other similar gobioids exhibit evolution stemming from divergent ancestral stock. In other words, perspective has a lot to do with ones understanding of how two organisms are related; are they related because they look and act the same, or are they related because they evolved from closely related ancestors?

Members of the genus Nemateleotris hail from the Indo-Pacific basin. They are associated with the sandy or rubbly bases of coral reef structures, hard bottoms, or the seaward sides of reef slopes. Depth profiles vary according to species, but generally do not exceed 70m deep. N. magnifica is the shallowest species, living as close as 6m from the surface. It also has the widest geographic distribution, ranging from E. Africa to Hawaii. Its wide distribution and shallow habitat make it far easier to collect than specimens of the other two genera. N. decora and N. helfrichi are both restricted to the southwest pacific region, including the Coral and Philippine Seas. They also display similar depth profiles, varying from 25m to 70m deep. However N. helfrichi, as previously mentioned, is rare in waters less than 40m deep.

Nemateleotrids are protogynous (pronounced proto jye nuss) hermaphrodites. They are all born female, with the most dominant individual morphing into a male. They are thought to go through a larval stage at birth, which may be one reason that captive-rearing is largely unheard-of. A few anecdotal reports of these fish breeding in captivity exist, but there is no established methodology to make such a thing occur. In the aquarium setting, breeding is further prevented by the fishs general attitude toward conspecifics, which can include excessive aggression. Though some firefish do well in small groups, others do not. They are commonly kept individually, as a result. The other nemateleotrids are even less tolerant of their own kind, and are best kept apart from members of the same species.


Aquarium Care:

Firefish and their close kin are excellent aquarium fish because they are hardy, reef-safe, and get along well with other fish, as long as they are not overly active. Wrasses, angelfish, and other energetic fish may cause nervousness in firefish, causing them to hide and refuse food. They also do not compete for food well with active species. They are small, and so should not be kept with large, aggressive carnivores. Fortunately, firefish are very reef-safe and do great in the rocky, sandy environment of a coral tank.

There is nothing unusual about the water quality recommendations for firefish, and keeping them in coral-quality water is optimal. It is important to note that lighting may be a factor in the long-term health of these fishes, as N. magnifica is the only species that exists in heavily-lit habitats. Therefore it behooves the aquarist to consider purchasing the other two only if appropriately dimmed conditions can be createdat least until the fish has fully acclimated. At that point, it may be possible to slowly raise the lighting threshold.

Feeding is relatively easy. Nemateleotrid dartfish are basically planktivores. They will eat very small meaty offerings, so long as they are suspended in the water column. Live brine shrimp work well because they stay suspended on their own, but a varied diet is always best to maximize health and colorization. Because they have relatively small guts, feed these dartfish twice daily to ensure excellent nutrition.

One final note on Nemateleotrid dartfish is a word of caution. Some of these fish are collected using detrimental practices. Take care to observe one before purchasing, looking for signs of poor swimming that might be indicative of decompression related injuries. The head should be angled upward, not down, and the animals should exhibit a good appetite. Unfortunately, cyanide (CN-) is commonly used in the collection of firefish, and 25% of imported specimens sampled between 1996 and 1999 showed some level of the deadly chemical. While the use of cyanide has been reduced since then among fishermen, it is always best to purchase these fish from reputable suppliers such as Quality Marine. We source all our fish from the most responsible supply lines across the globe and only pursue supply lines which employ safe animal collection techniques, no matter what the cost.





Works Cited:

Goemans, B. and L. Ichinotsubo. The Marine Fish Health and Feeding Handbook. T.F.H. Publications; Neptune City. 2008.

Jennings, Greg. The New Encyclopedia of the Saltwater Aquarium. Buffalo : Firefly books Ltd., 2007.

Lieske, Ewald and R. MeyersCoral Reef Fishes, Revised EditionPrinceton University Press: Princeton, 2001.

Simon and Schuster. Simon and Schuster's Guide to Freshwater and Marine Aquarium Fishes. New York : Fireside Books, 1977.

Staff. Purple Firefish. Fishlore Tropical Fish Information. URL: http://www.fishlore.com/profile-purplefirefish.htm