15. Feb, 2016

Life of a goby

Gobies are small fishes varying in size  between 2 and 20 cm. They belong  to one of the largest fish families, the Gobiidae  comprising more than 2,000 species in more than 200 genera. Best known is the subfamily of Gobiinae, also known as the true gobies*,  that contains more than 60 genera and 1120 species (note that the  biological hierarchy  spreads from:  family→ subfamily →genus →species).  As such, gobies  are a good  example of the amazing variety in adaptations of some fish species to its environment.

Most gobies have a large head and eyes, two dorsal fins, large pectoral fins, and  pouting cheeks.  They have an elongated transparent or coloured body with scales, often covered with bands or patches.  Most species have  fused pelvic fins that form a disc-shaped sucker (somewhat like the dorsal suckers of remoras). The goby uses it to attach  itself to rocks or coral branches. Gobies are found everywhere over the world in tropical and temperate, brackish and freshwater environments. Most species seem to prefer shallow habitats like tide pools, coral reefs, mangrove swamps (like the mud jumpers) and sea grass floors. A special genus from the subfamily of Gobiinae  is  Bryaninops, or sea whip (or whip-coral) goby  from  the  tropical Indo-Pacific waters. This genus can be split up in 16 species one of which (shown on the front page)  is Bryaninops yongei.  This  species uses gorgonians and black coral as its host (Cirrhipathes anguina). The whip coral goby has a semi-transparent head and body and it spawns on its host, the gorgonian**

Gobies usually live in male-female pairs. Many of them are bottom dwellers with habitats in the vicinity of a sandy bottom. Here there construct burrows (holes in the sand), using their mouths to dig into the sea bottom and by fanning away sand. The burrows are used as a hiding place as well as nests for spawning. The entrance of the  burrows are blocked with small pieces of coral or rubbish. The goby also builds a mound (a small hill of sand)  over the entrance of their burrow. Sometimes the burrow is shared with a little shrimp (see picture above, taken by Jan Derk  in April 2004 in Koh Tao, Thailand).  Initially male gobies are more active with maintaining the burrow. But after spawning the female takes over the maintenance, while males guard the eggs and provide them with oxygen by fanning water over them.

Some smaller male gobies  play a interesting role during the process of  spawning. Since female gobies seem to prefer large males, the small guys must find a strategy to deliver their sperm. This process is also called kleptogamy (secrete fertilization). So the small goby, also called sneaker approaches the spawning place of the official couple, and waits for the opportunity to  release its sperm when the  female releases her eggs. The sneaker often gets away with it,  probably because he is small and hardly distinguishable from females. The sneakers  don’t have to go through the trouble  of burrow building,  maintenance and parental care. So that’s a clear benefit, and a way to save energy. But there is also a cost involved: namely  the risk of being attacked or even killed  by the larger official male, in flagrante delicto

Sources:

Patzner, R.A.; Van Tassell, J.L.; Kovačić, M.; Kapoor, B.G., eds. (2011). The Biology of Gobies. Enfield.

*https://en.wikipedia.org/wiki/Goby

**https://en.wikipedia.org/wiki/Gobiinae

http://fishbase.sinica.edu.tw/summary/SpeciesSummary.php?ID=7251&AT=Whip-coral+goby