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Dive Dry with Dr. Bill

#725: Black-eyed Goby

In the past I 've written about some pretty colorful critters found beneath the waves. This week I thought I'd shift gears (even though my current car has an automatic transmission) and focus on one of the least spectacular denizens of the deep. Yep, this week's subject is the dull, drab black and white black-eyed goby (Rhinogobiops nicholsii).

They may reach a whopping six inches in length. As its common name suggests, one distinguishing feature of this small fish is its large black eyes. The tip of their first dorsal fin is also black. The ones I usually see are a ghostly white although on occasion they may be yellowish or greenish. Likewise, the majority I observe here have pretty uniform bodies with little or no markings. Dr. Milton Love states that they can display blotches, bands and saddles. Hmmm, I thought only horses had the latter.

I am told its geographic range extends from SE Alaska to central Baja. I can't verify the northern extent because you'll never find me diving such chilly waters! Warm is wonderful. Milton says they can be found in depths from the intertidal to more than 2,100 feet. I'll have to accept that fishy expert's data since you'll never find me diving that deep either unless James Cameron takes me on a submersible ride!

These gobies prefer areas with structure so they can hide in the nooks and crannies when I point my camera at them. They are rarely observed over flat, soft substrates unless shelter is close by. For little guys they are fairly aggressive and will defend their territories vigorously by extending their fins and facing off with their mouths agape. However, I'm brave enough not to wither under such an assault.

Researchers have described their 10-30 minute mating behavior this way. Males scrape out a depression under a rock and clean its under surface. To attract a potential mate, the male rises up into the water column several inches, spreading its fins to draw her attention. Works every time... not! Believe me, I've tried it. Dr. Love reports that the males pelvic fins darken during the mating period. Maybe that's where I've gone wrong?

If successful in his mating endeavors, the male ends up doing the child (or egg) rearing. Females may produce over 11,000 tiny eggs at a time, and a single male may entice as many as half a dozen ladies into his nest. Wonder if the poor boy knew what he was getting into. Papa Goby guards the nest and fans it to ensure proper circulation and an adequate supply of oxygenated water. Nests are about four inches and initially contain pale pink eggs that later turn gray. Milton reports that small males referred to as "sneakers" may try to enter the nest and fertilize the eggs themselves.

Even though I wrote a column about goby sex life several years ago, I had forgotten that these gobies are sequential hermaphrodites. All start out as females (perhaps the reason the fresh eggs are pink?). Some change to mature males and others continue to develop into mature females and later change gender. Here in the warmer waters of SoCal, these gobies may spawn year-round although in the colder waters further north and down deep mating may be much more limited.

Black-eyed gobies chow down on small crustaceans, worms, brittle stars and molluscs. They may only live a brief three years, although some become geriatrics surviving until age five. Of course that assumes they escape predators including many species of fish, cormorants and even marine mammals like harbor seals and sea lions. Fortunately for them they are much too small to entice anglers into serving filet of goby.

© 2017 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Black-eyed goby and close-up; goby fleeing from my camera and one using the empty shell
of a wavy top snail as a hiding place..

This document maintained by Dr. Bill Bushing.
Material and images © 2017 Star Thrower Educational Multimedia