Fish
Goby
Gobiidae · also called gobies
Most people have never heard of a goby, and yet on a tropical reef or a rocky shore the gobies may be the most numerous fish there. The family is one of the largest of all vertebrate families — more than 2,000 species — built around small, short-lived fish that cling to the bottom with a suction cup made from their own fins.
Overview
Gobies are the family Gobiidae, well over 2,000 species, in all warm and temperate seas and many fresh waters, on every continent except Antarctica. They are mostly small bottom fish — many under a few centimetres — of reefs, rocky shores, tide pools, estuaries, and streams. Most feed on small invertebrates picked from or filtered out of the sediment.
The sucker
In most gobies the two pelvic fins are fused into a single cup under the chest that works as a suction disc, letting the fish hold station on rock, coral, or a vertical face in surge and current that would sweep a free-swimming fish away. Some tropical stream gobies use it to climb waterfalls tens of metres high to reach adult habitat.
Small and fast
Several gobies mature at under 1 cm, and the dwarf pygmy goby is among the smallest vertebrates known. Many live only a year or less, maturing fast, breeding, and dying — one of the shortest life cycles of any vertebrate.
Partnerships and invasions
Many sand gobies share a burrow with a near-blind pistol shrimp: the shrimp digs, the goby watches for predators and signals danger with a tail flick. Meanwhile the round goby, carried from the Black Sea in ballast water, has become a damaging invader in the Great Lakes, the Baltic, and western European rivers.
Status
Gobies as a family are Not Evaluated. Most are abundant, but several spring and freshwater species with tiny ranges are threatened, and a few gobies have become serious invasive species.
Goby: common questions
Why are there so many species of goby?
Gobies are small, they mature fast, and they are strongly tied to particular patches of bottom habitat, all of which speeds up the formation of new species. A goby often spends its whole adult life in one crevice, one burrow, or one stretch of reef, so populations on separate reefs, islands, or river systems rarely mix and can diverge into distinct species. Short generations mean this happens quickly in evolutionary terms. The family has also repeatedly evolved specialists, cave gobies, coral-dwelling gobies, sponge gobies, shrimp-partner gobies, freshwater and spring gobies, each opening further room to diversify. The result is a family that keeps producing new species and now numbers in the thousands.
How does the goby and pistol shrimp partnership work?
It is a mutual arrangement between two very different animals sharing one burrow in the sand. The pistol shrimp is an energetic digger but has poor eyesight, so it does the construction and maintenance work, constantly bulldozing sand out of the tunnel. The goby has good vision and acts as the lookout, resting at the burrow mouth while the shrimp works. The shrimp keeps one long antenna touching the goby at all times, and when the goby detects a predator it flicks its tail against the antenna, and both animals dart into the burrow. The goby gets a ready-made shelter it could not dig, and the shrimp gets a warning system.
Are gobies the same as blennies?
They look alike and share the same shallow bottom-dwelling niche, but they are separate groups. The quickest field mark is the pelvic fins. Gobies have theirs fused, or nearly so, into a single disc under the throat, while blennies have separate pelvic fins set far forward, ahead of the pectorals. Blennies also tend to have blunter heads, often with fringed flaps called cirri above the eyes, a single long continuous dorsal fin, and no scales, whereas many gobies have two separate dorsal fins and small scales. Both families are large and both are full of small, territorial, crevice-loving fish, which is why they are so often confused.
Why is the round goby a problem in the Great Lakes?
The round goby is native to the Black and Caspian Sea region and reached the Great Lakes in the 1990s in the ballast water of ships. It has thrived there because it tolerates poor conditions, breeds several times a season, aggressively defends nest sites, and eats the eggs and young of native fish as well as the invasive zebra and quagga mussels. It has displaced native bottom fish such as sculpins and darters from prime habitat and competes with sport fish for food and spawning areas. On the other side, some larger predators and birds now feed heavily on round gobies, which unfortunately also passes accumulated contaminants up the food chain.