Palmtail Goby, Gobionellus microdon

Palmtail Goby, Gobionellus microdon. Fish caught with a cast net from coastal brackish waters off Mazatlán, Sinaloa, October 2018. Length: 17 cm (6.7 inches). Photograph courtesy of George Brinkman, Guelph, Ontario, Canada.

The Palmtail Goby, Gobionellus microdon, is a member of the Goby or Gobiidae Family, that is also known as the Estuary Goby and in Mexico as gobio cola de palma. Globally, there are eleven species in the genus Gobionellus, two of which are found in Mexican waters, one in the Atlantic and one, this species, in the Pacific Ocean.

The Palmtail Goby has an elongated, compressed body, with a slight compressed head and a broadly rounded snout with large eyes set high on the sides of the head. They are light tan in color with a silvery sheen with irregular brown oblique, forward-pointing saddles on the back, a row of dark blotches separated by dark spots on the flank transitioning ventrally to silvery with 6 dark wavy bars. The caudal fin has rows of spots that form bars; the dorsal fin has spots that form stripes. They are sexually dimorphic with the females having a gray anal fin and a dark gray pelvic fin with a white border and the males having a darker gray anal fin and dark gray pelvic fins without a white border. They have an oblique mouth that opens in the front that is equipped with fine numerous teeth in 1 to 3 rows on the top jaw and 2 or 3 rows on the bottom jaw. Their anal fin has 1 spine and 12 or 13 rays; their caudal fin is rounded and much longer than the head; their first dorsal fin has six spines, the first of which is elongated in males, and the second separate dorsal fin has 1 spine and 12 rays; and their pelvic fins have 1 spine and 5 rays that are fused into a sucking disc. They have a total of 13 to 15 gill rakers and are covered with small scales.

The Palmtail Goby is a small shallow-water species found in estuaries and brackish mangrove creeks at depths up to 5 m (15 feet). They reach a maximum of 22.4 cm (8.8 inches) in length. The Palmtail Goby is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

In Mexican waters the Palmtail Goby is a resident of the Pacific but has a limited distribution being found from La Paz to Cabo San Lucas, Baja California Sur, along the east coast of Baja and from Hermosillo, Sinaloa, south to Guatemala along the west coast of the mainland.

The Palmtail Goby is most likely confused with the Longtail Goby, Ctenogobius sagittula (5 dark blotches on the flanks), and the Mangrove Goby, Ctenogobius manglicola (black spot with an orange margin at the rear of the first dorsal fin).

From a conservation perspective the Palmtail Goby is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature and of limited interest to most.