|Sharknose Goby (E. evelynae)|
D. S. Jordan, 1904
D. S. Jordan, 1904
Elacatinus is a genus of marine gobies, often known collectively as the neon gobies. Although only one species, E. oceanops, is technically the "neon goby," because of their extremely similar appearance, other members of the genus are generally labeled neon gobies, as well. They are known for engaging in symbiosis with other marine creatures by providing them cleaning service that consists of getting rid of ectoparasites on their bodies. In return, Elacatinus obtain their primary source of food, ectoparasites.
Neon gobies are very small, torpedo-shaped fish. Although sizes vary slightly by species, they are generally about 2.5 cm (1 inch) long. They have dark bodies with iridescent stripes running from the tip of the nose to the base of the caudal fin. The color of the stripes varies by species. Like all gobies, their dorsal fin is split in two, the anterior dorsal fin being rounded like that of a clownfish and the posterior dorsal fin being relatively flat. The anal fin lines up with the posterior dorsal fin and is of similar shape. The pectoral fins are nearly circular, and, like all other fins, transparent.
Gobies of the genus Elacatinus mostly reside in the western Atlantic with the exception of one species Elacatinus oceanops that resides in the Caribbean Sea, the Florida Keys and the Bahama Islands. However, they have been found in northwestern Gulf of Mexico and along the northern Yucatan Peninsula. 
Elacatinus are generally carnivorous, with their primary diet consisting of ectoparasites on skins, fins, mouth and gill chambers of their clients.  Depending on their ecological circumstances, they may also feed on zooplankton and non-parasitic copepods.  Although they are carnivorous, Elacatinus occasionally consume algae and other plants as secondary food source. 
Some species of gobies exhibit gonochorism and protogynous hermaphroditism, including bi-directional sex reversal.  Protogyny refers to a category of hermaphroditism where female organs develop or mature before the appearance of male product. In most species of male Tellostei gobbidae this characteristic is observed.  Among those in the genus Elacatinus, protogyny is observed in E. illecebrosus.  Protogynous hermaphroditism in gobies consists of a male reproductive system with paired, secretory, accessory gonadal structures (AGS) associated with the testis.  While the AGS is almost universally present in male gobies, protogynous females need to develop AGS in order for sex reversal to take place. The AGS develop from precursive tissues (pAGS), in the form of bilateral, ventrally localized cell masses, located close to the junction of the ovarian lobes and the oviduct. At the time of sex change, it undergoes rapid growth and diverts to form the AGS.  When pAGS develops into AGS, ovigerous tissue is also completely replaced by seminiferous lobules. However, the ovarian lumen remains even after the sex change, functioning as a common spermatozoa collection region that is continuous with the common genital sinus as free spermatozoa travels from seminiferous lobules into the gonadal lumen. 
Gonochorism refers to development or evolution of sex.  Gonochoric goby species normally do not possess pAGS, but pAGS are observed in E. illecebrosus and E. evelynae. .  Specifically, the ovarian lobes of small-sized juvenile females of these species possess distinctive pAGS that started to diminish and then disappeared as they approach adulthood. 
Gobies are multiply spawning species, usually spawning from February to April. After spawning, male gobies guard and oxygenate eggs via frequent movement of their pectoral and caudal fins; males will consume any eggs affected by fungus. However, after hatching, the larvae receive no parental protection. Approximately 30 days after hatching, the larvae begin metamorphosis into juvenile goby. 
Elacatinus usually maintain social monogamy, a system in which heterosexual pairs remain closely associated during both reproductive and non-reproductive periods.  Male and female Elacatinus forage together, occupying a single cleaning station and servicing client fish in pair. Such behavior observed in Elacatinus is attributed to low costs and high benefits for both sexes that result from being paired with a single, large partner. Males benefit from forming monogamous pairs with large females since they tend to have higher fecundity, while females are able to gain more resources by cleaning under the protection of a larger male. Females would experience reduced cleaning rate overall when cleaning with a male. However, they were observed to spend more time in each cleaning session and therefore able to feed on more ectoparasites compared to those with a smaller mate. It is not confirmed if large body size also correlates with better paternal care, as it is difficult to observe caring behavior of Elacatinus whose males tend eggs that are laid deep within a small coral cavity. Intrasexual aggression used as a means to guard mates is proposed as a primary mechanism of maintaining monogamy. Both males and females were observed to be very aggressive toward same-sex intruders who come to their territory to accost their partners. However, several biological and ecological factors also enforce monogamy in these cleaner gobies. Elacatinus reproduce asynchronously, which makes polygyny unfavorable. Furthermore, although it differs among species, cleaner gobies tend to live in environments of low population density where distance between potential mates is rather far. Although it is seldom, polygyny is observed in Elacatinus. It is observed that mated males may approach a new female if she is larger than their mate. Polygyny may also be exhibited in widowed males and females. When Elacatinus are widowed, they often leave their cleaning territory. However, the vacant territory is not claimed by other cleaner gobies, which implies that the widowed gobies actually chose to move instead of being forced. This observation shows that the widowed gobies possibly have moved to search for new mate.
Mutualism refers to relationship where one or both partners provide a service or resources to the other. Elacatinus, or Caribbean cleaning gobies, engage in mutualism by removing and feeding on ectoparasites on their clients. They present themselves and wait for clients at cleaning stations, as they largely depend on cleaning for their diet. Elacatinus often clean in pairs, where pairs are most often composed of a male and a female. Occupying the same territory, the cleaner pair usually cleans the same client at the same time. 
Cleaning gobies generally service a wide range of clients; however, members of the genus Elacatinus are considered the most specialized cleaner gobies in tropical western Atlantic. Most frequent clients of Elacatinus include damselfish, Pomacentridae and grunts, Haemulidae and planktivores. Rather than seeking their client actively, they remain close to their cleaning station and seldom move more than a meter laterally. They do, however, dance in zig-zag swimming pattern to attract clients.  Hosts come to the cleaning sites and pose to show their intent to receive service. Such poses are usually directed at the cleaning station rather than the individual gobies.  However, not all the potential clients, or those who pose, are attended by cleaners. Duration of cleaning may range from couple seconds up to almost half an hour. In observational studies, decrease in cleaning frequency turned out to be correlated to increase in cleaning durations. The rate of feeding and cleaning duration most likely reflects the number of parasites on clients’ bodies. 
Elacatinus has a unique response to predators’ approach. Fish response to danger is largely classified into two: fight-or-flight or freezing. However, Elacatinus follows neither. It engages in cleaning interactions with potential predators sooner than with non-predatory clients, treating them almost as soon as they arrive at their cleaning stations. Furthermore, it was observed that the Elacatinus clean predators for longer durations. As implied by higher cortisol level in the Elacatinus when approached by predators, the fish do experience stress upon encountering predators, but unlike other fish that exhibit flight or freezing response, Elacatinus demonstrates a proactive response. It is predicted that Elacatinus chooses to be proactive as cleaning predators faster makes them leave sooner, which in turn would encourage non-predatory clients to revisit cleaning stations. Moreover, such proactive response may serve as a pre-conflict management strategy that might result in safe outcome for interactions with certain predators.
Common stripe patterns in Elacatinus include yellow, green and blue; however, those possessing blue stripes were found to be most effective in attracting clients as well as deterring predators. Four of six cleaner species of the Elacatinus genus display such coloration—E.oceanops, E.evelynae, E.genie and E.prochilos. E.puncticulatus and E.nesiotes engage in cleaner activity but do not possess blue stripes. One of the ways Elacatinus signals its clients is through unique blue stripes that distinguishes them from their non-cleaning sister species; while their non-cleaning relatives possess yellow or green stripes that blend well with their sponge dwellings, cleaning Elacatinus advertise their presence to potential clients by sitting on top of substrata such as coral. The characteristic blue stripe that is only observed in the cleaner lineage of gobies marks great contrast with the coral microhabitats compared to other stripe colors found in gobies, and therefore allow them to be spotted easily. Blue stripes of Elacatinus play a role as signals for cooperation in addition to advertisement. Additionally, it was observed in an experimental setting that Elacatinus possessing blue stripes deterred or survived significantly more attacks as compared to green and yellow gobies.
Some Elacatinus cleaners cheat by feeding on scales and mucus of clients in addition to ectoparasites on their clients, which is confirmed by examination of their stomach contents. However, cheating may result in punishment. When clients realize that they are being cheated on, they interrupt the cleaning interaction and swim away or do not return to the gobies' cleaning station in the future, which may result in the cheater obtaining less resource than they could have obtained without cheating. This client behavior is similar to sanction strategy, where one partner restrains its biological investment. This strategy has been proven effective in keeping interspecies mutualism stable,and such cheating behavior is not readily observed in Elacatinus.  They prefer to feed on ectoparasites over client mucus or scale. Therefore, it is most likely that they will cheat only when ectoparasites supply is depleted in clients.
In the aquarium
Members of the genus Elacatinus, particularly E. oceanops, are among the most popular marine aquarium inhabitants.
Several species of neon goby are readily available because of successful captive breeding programs, although scientific names are not always given. Generally, if the specimen has a blue stripe, it can be identified as E. oceanops, and if the stripe is half-blue half-gold, as E. evelynae. Various species are offered as "Gold Neon Gobies".
Neon gobies are not difficult to keep, and accept a wide variety of water parameters. Specific gravity is not critical, so long as it remains steady. As with all marine aquarium fish, they are sensitive to even trace amounts of ammonia or nitrite in an aquarium. Small amounts of nitrate are acceptable, but if over the long term these amounts increase, this can cause problems. Neon gobies are tolerant of a broad range of temperatures, but they are tropical so a heater may be necessary to maintain a temperature of at least 25°C (78°F) year round. Other parameters, such as alkalinity only become a problem if they are extreme.
Because of their small size, neon gobies are excellent Nano Reef inhabitants, and can live in tanks as small as five gallons, but a ten gallon or larger tank is more appropriate for best health (and ease of care). In larger tanks, they can be kept in groups. Neon gobies are suitable for all types of marine aquariums, with the exception of those which contain large predatory fish or invertebrates which might attempt to eat the gobies. They need plenty of hiding places, and they make excellent reef inhabitants. They are not picky eaters, and will accept any and all frozen or live foods. They can also be easily trained to take flake or pellet foods, but a variety of frozen, freeze dried, and live foods to supplement a prepared staple is the best feeding routine. They are sometimes shy eaters and may be out-competed for food by more boisterous and aggressive feeders.
If kept in pristine conditions and fed well, neon gobies will readily spawn in home aquaria. A species or breeding tank is required, as the fry are small and will be eaten by most other fish. The gobies are sexually dimorphic, but the difference is not easy to ascertain, so they are normally kept in large groups to ensure a balance of sexes. They will lay their eggs on any hard surface along the bottom, and the fry, which feed on small rotifers or other microscopic organisms, are fully developed within a month. The average lifespan for a neon goby is approximately a year to a year and a half.
There are currently 34 recognized species in this genus:
- Elacatinus atronasus (J. E. Böhlke & C. R. Robins, 1968)
- Elacatinus chancei (Beebe & Hollister, 1933) (Shortstripe goby)
- Elacatinus colini J. E. Randall & Lobel, 2009
- Elacatinus digueti (Pellegrin, 1901) (Banded cleaner goby)
- Elacatinus dilepis (C. R. Robins & J. E. Böhlke, 1964) (Orangesided goby)
- Elacatinus evelynae (J. E. Böhlke & C. R. Robins, 1968) (Sharknose goby)
- Elacatinus figaro I. Sazima (fr), R. L. Moura & R. de S. Rosa, 1997 (Barber goby)
- Elacatinus gemmatus (Ginsburg, 1939) (Frecklefin goby)
- Elacatinus genie (J. E. Böhlke & C. R. Robins, 1968) (Cleaner goby)
- Elacatinus horsti (Metzelaar, 1922) (Yellowline goby)
- Elacatinus illecebrosus (J. E. Böhlke & C. R. Robins, 1968) (Barsnout goby)
- Elacatinus janssi W. A. Bussing, 1981 (Spotback goby)
- Elacatinus jarocho M. S. Taylor & Akins, 2007 (Jarocho Goby)
- Elacatinus limbaughi Hoese & Reader, 2001 (Widebanded cleaning goby)
- Elacatinus lobeli J. E. Randall & P. L. Colin, 2009
- Elacatinus lori P. L. Colin, 2002
- Elacatinus louisae (J. E. Böhlke & C. R. Robins, 1968) (Spotlight goby)
- Elacatinus macrodon (Beebe & Tee-Van, 1928) (Tiger goby)
- Elacatinus multifasciatus (Steindachner, 1876) (Greenbanded goby)
- Elacatinus oceanops D. S. Jordan, 1904 (Neon goby)
- Elacatinus pallens (Ginsburg, 1939) (Semiscaled goby)
- Elacatinus panamensis Victor, 2010 (Panamanian greenbanded goby)
- Elacatinus phthirophagus I. Sazima (fr), Carvalho-Filho & C. Sazima, 2008 (Noronha cleaner goby)
- Elacatinus pridisi R. Z. P. Guimarães, Gasparini & L. A. Rocha, 2004
- Elacatinus prochilos (J. E. Böhlke & C. R. Robins, 1968) (Broadstripe goby)
- Elacatinus puncticulatus (Ginsburg, 1938)
- Elacatinus randalli (J. E. Böhlke & C. R. Robins, 1968) (Yellownose goby)
- Elacatinus redimiculus M. S. Taylor & Akins, 2007 (Cinta Goby)
- Elacatinus rubrigenis Victor, 2010
- Elacatinus saucrus (C. R. Robins, 1960) (Leopard goby)
- Elacatinus serranilla J. E. Randall & P. L. Colin, 2009
- Elacatinus tenox (J. E. Böhlke & C. R. Robins, 1968) (Slaty goby)
- Elacatinus xanthiprora (J. E. Böhlke & C. R. Robins, 1968) (Yellowprow goby)
- Elacatinus zebrellus (C. R. Robins, 1958) (Zebrette goby)
- E. oceanops, Fishbase. http://www.fishbase.org/Summary/SpeciesSummary.php?id=3876
- E. oceanops, Fishbase. http://www.fishbase.org/Summary/SpeciesSummary.php?id=3876
- "Elactinus Research: Introduction". Retrieved November 13, 2013.
- Patzner, Robert. The biology of gobies. Science Publishers. p. 291-307. ISBN 9781578084364.
- Arnal C, CÂotÉ IM. (June 1998). "Interactions between cleaning gobies and territorial damselfish on coral reefs". Animal Behavior 55 (6): 1429–1442. 10.1006/anbe.1998.0727.
- Meirelles, M. E., Tsuzuki, M. Y., Ribeiro, F. F., Medeiros, R. C. and Silva, I. D. (June 2009). "Reproduction, early development and larviculture of the barber goby, Elacatinus Figaro". Aquaculture Research 41 (1): 11–18. 10.1111/j.1365-2109.2009.02295.x.
- "Protogyny". Merriam-Webster Dictionary. http://www.merriam-webster.com/: An Encyclopedia Britannica Company. 2013.
- Yvonne Sadovy De Mitcheson, Min Liu (February 2008). "Functional hermaphroditism in teleosts". Fish and Fisheries 9 (1): 1–43. 10.1111/j.1467-2979.2007.00266.x.
- Cole, Kathleen S. Reproduction and sexuality in marine fishes. Berkeley: University of California Press. p. 129. ISBN 9780520947979.
- Kathleen S. Cole (July 2008). "Transient ontogenetic expression of hermaphroditic gonad morphology within the Gobiosoma group of the Neotropical seven-spined gobies (Teleostei: Gobiidae)". Marine Biology 154 (6): 943–951. 10.1007/s00227-008-0986-z.
- Elizabeth A. Whiteman, Isabelle M.Côté (August 2003). "Social monogamy in the Cleaning goby Elacatinus evelynae: ecological constraints or net benefit?". Animal Behaviour 66 (2): 281–291. 10.1006/anbe.2003.2200.
- Davies, Nicholas B. (2012). An Introduction to Behavioural Ecology. John R. Krebs, Stuart A. West. John Wiley & Sons, Ltd. p. 159. ISBN 978-1-4051-1416-5.
- M.C. Soares, I.M. Côté, S.C. Cardoso & R.Bshary (August 2008). "The cleaning goby mutualism: a system without punishment, partner switching or tactile stimulation". Journal of zoology 276 (3): 306–312. 10.1111/j.1469-7998.2008.00489.x.
- Ivan Sazima, Cristina Sazima, Ronaldo B. Francini-Filho, Rodrigo L. Moura (September 2000). "Daily cleaning activity and diversity of clients of the barber goby, Elacatinus figaro, on rocky reefs in southeastern Brazil". Environmental Biology of Fishes 59 (1): 69–77. 10.1023/A:1007655819374.
- Marta C. Soares, Redouan Bshary, Sónia C. Cardoso, Isabelle M. Côté, Rui F. Oliveira (June 2012). "Face Your Fears: Cleaning Gobies Inspect Predators despite Being Stressed by Them". PLoS ONE 7 (6): e39781. 10.1371/journal.pone.0039781.
- L. Lettieri & J.T. Streelman (November 2010). "Colourful stripes send mixed messages to safe and risky partners in a diffuse cleaning mutualism". Journal of Evolutionary Biology 23 (11): 2289–2299. 10.1111/j.1420-9101.2010.02098.x.
- Marta C. Soares, Redouan Bshary, Isabelle M.Côté (October 2009). "Cleaning in pairs enhances honesty in male cleaning gobies". Behavioral Ecology 20 (6): 1343–1347. 10.1093/beheco/arp138.
- Fenner, Robert M. The Conscientious Marine Aquarist. Neptune City, NJ, USA: T.F.H. Publications, 2001.
- Froese, Rainer, and Daniel Pauly, eds. (2013). Species of Elacatinus in FishBase. June 2013 version.
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