Gobiidae
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The Gobies form the family Gobiidae, and is one of the largest families of fish, with over 2000 nominal species. Most are relatively small, typically less than 10cm (4in) in length. Gobies include some of the smallest vertebrates in the world, like species of the genera Trimmaton, Tyson and Pandaka, which are under 1cm (3/8in) long when fully grown. Up to 2006 the smallest described vertebrate was the goby Schlinderia brevipinguis (Watson & Walker, 2004), but seemingly this guinness has been beaten by the cyprinid Paedocypris progenetica (Kottelat. et al., 2006), whose smallest mature female measured was a mere 7.9mm. There are some large gobies, such as species of Gobioides, that can reach well over 30cm (1ft) in length, but that is exceptional. Although few are important as food for humans, they are of great significance as prey species for commercially important fish like cod, haddock, sea bass, and flatfish. Several gobies are also of interest as aquarium fish, such as the bumblebee gobies of the genus Brachygobius.
The most distinctive aspect of goby morphology are the fused pelvic fins that form a disc-shaped sucker. This sucker is functionally analogous to the dorsal fin sucker possessed by the remora or the pelvic fin sucker that the lumpfish, but is anatomically distinct, and these similarities are the product of convergent evolution. Gobies can often be seen using the sucker to adhere to rocks and corals, and in aquaria they will happily stick to glass walls of the tank as well.
Gobies are primarily fish of shallow marine habitats including tide pools, coral reefs, and seagrass meadows; they are also very numerous in brackish water and estuarine habitats including the lower reaches of rivers, mangrove swamps, and salt marshes. A small number of gobies (unknown exactly, but in the low hundreds) are also fully adapted to freshwater environments. These include the Asian river gobies (Rhinogobius spp.), the desert gobies of Australia (Redigobius), and the European freshwater goby Padagobius martensii.
The "sleeper gobies" (Eleotridae) are a closely-related family.
Mudskippers
Many marine fish live in intertidal habitats, surviving the retreat of the tide by hiding under wet seaweed or by using temporary tide pools. Mudskippers instead, gobies of the subfamily Oxudercinae, are uniquely adapted to a completely amphibious lifestyle (Murdy, 1989). Mudskippers are found only in tropical and subtropical regions, having a geographical distribution that includes all the Indo-Pacific and the Atlantic coast of Africa. Mudskippers are very active when out of water, feeding and interacting with one another, for example to defend their territories.
Mudskippers display a range of behavioural and physiological adaptations. Compared with normal, fully aquatic gobies, these include:
- Anatomical and behavioural adaptations that allow them to move effectively on land as well as in the water (Harris, 1961).
- The ability to breathe through their skin and also through the lining of the mouth (the mucosa) and throat (the pharynx). This is only possible when the mudskipper is wet, limiting mudskippers to humid habitats and requiring that they keep themselves moist. This mode of breathing, similar to that employed by amphibians, is known as cutaneous breathing (Graham, 1997).
- Digging of deep burrows in soft sediments that allow the fish to thermoregulate; avoid marine predators during the high tide when the fish and burrow are submerged; and for laying their eggs (Sasekumar et al., 1994; Tytler & Vaughan, 1983; Brillet, 1969).
Even when their burrow is submerged, mudskippers maintain an air pocket inside it which allow them to breathe in conditions of environmental very low oxygen concentration (Ishimatsu et al., 1998; 2000; Lee et al., 2005).
The diverse and widespread genus Periophthalmus is by far the most diverse genus of mudskipper. Seventeen species are currently recognised (Larson & Takita, 2005). Periophthalmus argentilineatus is one of the most widespread and well known mudskippers. This species can be found in mangrove ecosystems and mudflats of East Africa and Madagascar east through South East Asia to Northern Australia, Hong Kong and Japan, up to Samoa and Tonga Islands (Murdy, 1989). It grows to a length of about 6 in (15 cm) and is a carnivorous opportunist feeder. It feeds on small preys such as small crabs and other arthropods (Milward, 1974). Another species, Periophthalmus barbarus, is the only oxudercine goby that inhabits the coastal areas of Western Africa (Murdy, 1989). Both these mudskippers are widely traded as aquarium fish.
Symbiosis
Some goby species live in symbiosis with burrowing shrimps. The shrimp maintains a burrow in the sand in which both the shrimp and the goby fish live. The shrimp has poor eyesight compared to the goby, but if it sees or feels the goby suddenly swim into the burrow, it will follow. The goby and shrimp keep in contact with each other, the shrimp using its antennae, and the goby flicking the shrimp with its tail when alarmed. These gobies are thus sometimes known as 'watchman gobies'.
Another example of symbiosis is demonstrated by the neon gobies (Gobiosoma spp.). These gobies are cleaner fish, and remove parasites from the skin, fins, mouth, and gills of a wide variety of large fish. The most remarkable aspect of this symbiosis is that many of the fish that visit the cleaner gobies' cleaning station would otherwise treat such small fish as food (for example groupers and snappers).
Gobies in aquaria
Several species of goby are kept in aquaria. The bumblebee gobies, genus Brachygobius are perhaps the most widely traded examples, being small, colourful, and easy to care for. They need tropical, hard and alkaline freshwater or slightly brackish conditions to do well. Gobies are generally peaceful towards their tankmates though territorial among themselves. Since most are small and few are predatory towards other fishes, they usually make good community fishes. Typically, the main problem with gobies is feeding them: with a few exceptions, the small species kept in aquaria prefer live or frozen foods rather than flake, and they are not very good at competing with active species such as cichlids. It is often recommended that gobies be kept on their own or with peaceful surface dwelling species such as halfbeaks and guppies.
See also
- List of fish common names
- List of fish families
- Blenny (another family of shallow water marine fish often confused with gobies)
- Dragonet (superficially similar to gobies and sometimes confused with them)
References
- Brillet C., 1969. Etude du comportement constructeur des poissons amphibies Periophthalmidae, Terre et la Vie, 23 (4): 496–520.
- Graham J.B., (editor) 1997. Air–breathing Fishes. Evolution, Diversity and Adaptation, Academic Press, San Diego California, 299 pp.
- Harris V.A., 1961. On the locomotion of the mudskipper Periophthalmus koelreuteri (Pallas): Gobiidae, Proceedings of the Zoological Society of London, 134: 107-135.
- Ishimatsu A., Hishida Y., Takita T., Kanda T., Oikawa S., Takeda T. & Khoo K.H., 1998. Mudskipper Store Air in Their Burrows, Nature, 391: 237–238.
- Ishimatsu A., Takeda T., Kanda T., Oikawa S. & Khoo K.H., 2000. Burrow environment of mudskippers in Malaysia, Journal of Bioscience, 11 (1,2): 17–28.
- Kottelat, M.; Britz, R.; Hui T.H. & Witte K.-E., 2006. Paedocypris, a new genus of Southeast Asian cyprinid fish with a remarkable sexual dimorphism, comprises the world’s smallest vertebrate. Proceedings of the Royal Society B, publ. online: 1-5.
- Larson H.K. & Takita T., 2005. Two new species of Periophthalmus (Teleostei: Gobiidae: Oxudercinae) from northern Australia, and a re-diagnosis of Periophthalmus novaeguineaensis, The Beagle, Records of the Museums and Art Galleries of the Northern Territory, 20: 175-185.
- Lee H.J., Martinez C.A., Hertzberg K.J., Hamilton A.L. & Graham J.B., 2005. Burrow air phase maintenance and respiration by the mudskipper Scartelaos histophorus (Gobiidae: Oxudercinae), The Journal of Experimental Biology, 208: 169-177.
- Milward N.E., 1974. Studies on the taxonomy, ecology and physiology of Queensland mudskippers, unpub. Ph D. dissertation, Univ. Of Queensland, Brisbane, Australia, 276 pp.
- Murdy E.O., Takita T., 1999. Periophthalmus spilotus, a new species of mudskipper from Sumatra (Gobiidae: Oxudercinae), Ichthyological Research, 46 (4): 367–370.
- Sasekumar, A.; Chong, V.C.; Lim, K.H. & Singh, H.R., 1994. The Fish Community of Matang Mangrove Waters, Malaysia – Sudara, S.; Wilkinson, C.R.; Chou, L.M. (eds). Proceedings, Third ASEAN-Australia Symposium on Living Coastal Resources. Research papers. Chulalonghorn University, Bangkok, Thailand. Vol. 2: 457-464.
- Schäfer, Frank 2005. Brackish-Water Fishes, Aqualog. ISBN 3-936027-82-X (English), ISBN 3-936027-81-1 (German)
- Tytler P. & Vaughan T., 1983. Thermal Ecology of the Mudskippers Periophthalmus koelreuteri (Pallas) and Boleophthalmus boddaerti (Pallas), of Kuwait Bay, Journal of Fish Biology, 23 (3): 327–337.
- Watson, W. & Walker H.J. Jr., 2004. The World’s Smallest Vertebrate, Schindleria brevipinguis, A New Paedomorphic Species in the Family Schindleriidae (Perciformes: Gobioidei). Records of the Australian Museum, 56: 139-142.