Yellowfin Goby, Acanthogobius flavimanus

Yellowfin Goby, Acanthogobius flavimanus. Fish caught from Suisun Slough within the greater San Francisco Bay area, California, August 2019. Length: 13.0 cm (5.1 inches). Catch, photograph, and identification courtesy of Kenneth Tse, Toronto, Canada.

Yellowfin Goby, Acanthogobius flavimanus. Fish caught from a brackish intertidal lagoon in Fukuoka, Japan, July 2012. Length: 13.5 cm (5.3 inches). Catch, photograph, and identification courtesy of Ben Cantrell, San Diego, California.

Yellowfin Goby, Acanthogobius flavimanus. Fish caught from within Mission Bay, San Diego, California, October 2019. Length: 15.1 cm (5.9 inches). Catch, photograph, and identification courtesy of Ben Cantrell, San Diego, California.

Yellowfin Goby, Acanthogobius flavimanus. Fish caught from within San Francisco Bay, San Francisco, California, October 2021. Length: 20 cm (7.9 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

The Yellowfin Goby, Acanthogobius flavimanus, is a member of the Goby or Gobiidae Family, and is known in Mexico as gobio extranjero. Globally, there are six species in the genus Acanthogobius of which only this species is found in Mexican waters, and it in the Pacific Ocean.

The Yellowfin Goby has an elongated body with a blunt head. Their eyes are set close together on top of their head and their mouth terminates at the middle of the eyes. They are an overall drab gray brown to light brown color with darker saddle markings and dusky spots that transitions to white ventrally. Their head has a small mouth that ends well before the eyes. Their caudal fin and two dorsal fins are rows of spots; the pectoral and pelvic fins are yellow. The anal fin has 11 or 12 rays; their caudal fin is rounded; their first dorsal fin has 8 spines; their second dorsal fin has 14 rays; and, their pelvic fins are fused and form a large sucking disc.

The Yellowfin Goby is found within muddy and sandy bottoms along the shores of bays and estuaries in the intertidal zone and in fresh water environments just above the tidal influence at depths up to 6.5 m (21 feet). They are euryhaline capable of surviving a broad range of salinities. They are known to enter estuaries and live in fresh water environments for extended periods of time. They reach a maximum of 30.0 cm (11.8 inches) in length. They are poor swimmers and are lie-in-wait ambush predators that consume amphipods, bivalves, copepods, detritus, fly larvae, small fish, mantis shrimp, mysids and polyschaetes. In turn they are preyed upon by numerous larger fish including the Leopard Shark, Triakis semifasciata and Pacific Harbor Seals, Phoca vitulina. They are known to be heavily infested with copepods and numerous parasites. The females reach sexual maturity in two years and the males in one year. Reproduction commences with a migration downstream in fresh water environments to spawn in coastal estuaries. Reproduction is oviparous with males constructed Y-shaped 14-inch deep burrows and tunnels with two entrances within the mud and coarse sandy substrate. Each female will lay between 6,000 and 32,000 eggs which are attached to the roof of the tunnel and then fertilized by the males. The eggs are then guarded by the males, and occasionally the females, for 28 days. Their larvae are pelagic and disperse rapidly utilizing the tidal flow to move upstream and then hold their position with their sucking disc when the tide changes. They have lifespans of up to three years. The Yellowfin 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.

The Yellowfin Goby is fairly easy to identify as it is by far the largest goby found in Mexican waters and unlike all other gobies has yellow ventral fins. They are similar however, to the Longjaw Mudsucker, Gillichthys mirabilis (large mouth that extends past the eye).

The Yellowfin Goby is a resident of Mexican waters of the Pacific Ocean but has a very limited distribution being found from Ensenada, Baja California, northward along the extreme northwest coast of Baja California. It is a native of the Sea of Japan (China, Japan and Korean waters) and is believed have been introduced via ballast water and hull fowling into all of the major West Coast ports of the United States and has now spread southward. An alternative theory is that they were introduced as eggs attached to oysters growing on ship hulls.

From a conservation perspective the Yellowfin Goby is currently considered to be of Least Concern with stable, widely distributed populations. They are considered to be highly invasive and strongly compete with native and endangered species for food. They are small in stature and are of little interest to most. They are utilized as a live bait by recreational anglers which has enhanced their range. They are utilized by the aquarium trade as a modest level and are also a component of Chinese medicine.