Blackeye Goby

Blackeye gobies can easily be identified by the fleshy crest on the upper surface of their heads, the distinctive black upper anterior edge of the first dorsal fin, their large scales, and large, dark eyes. They are small fish, reaching a maximum length of only 15 cm (6 in).

The body is elongated, slightly compressed, and almost completely covered by scales. The head lacks scales and is wider than it is deep, with a small terminal mouth and a projecting lower jaw. The maxilla does not extend below the anterior margin of the eye. The teeth are conical and are present in double rows on both jaws. The eyes are directed slightly upwards and sideways.

Blackeye gobies are found in the eastern North Pacific, along the coasts of Canada, the United States, and Mexico. It reaches as far north as St. John Baptist Bay (near Partofshikof Island) in Alaska to as far south as San Martin Island of Baja California, Mexico. Its range does not extend into the Gulf of California, however.

Blackeye gobies are diurnal, being primarily active during daytime. They feed almost exclusively on small crustaceans and mollusks. The most common prey include amphipods, copepods, isopods, decapods (particularly hermit crabs), snails, and clams. Other less important prey include annelids and other invertebrates. Parts of echinoderms (mostly sea urchins) and bryozoans are also found in the contents of the stomachs of blackeye gobies, though this is likely the result of incidental ingestion rather than true predation. The preferred prey can vary by season depending on their abundance. Blackeye gobies have also been observed feeding directly on chemosynthetic bacterial mats. It is of particular significance if substantiated, as it would be the first known instance of a fish deriving nutrition directly from chemosynthetic bacteria.

Blackeye gobies are highly territorial. Each male usually guards a harem of two to eight females and a small territory around a shelter. They are diurnal and mostly prey on small crustaceans and mollusks. They are protogynous hermaphrodites, with all individuals being born females and turning into males once they reach a certain size under the correct conditions. They exhibit courtship display and breed between April and October. The larvae are pelagic.

Blackeye gobies are sexually dimorphic, with different sexes distinguishable from genital papilla, size, and length of dorsal and anal fins. Females attain sexual maturity at 4.73 to 7.35 cm (1.86 to 2.89 in) in length, while males mature at 7.21 to 8.3 cm (2.84 to 3.27 in) in length. The breeding season lasts for five to seven months, between April and October. During this, the fused pelvic fins (the disk) of the males turn very dark in color.