Glass or Masked, Gobies We Hardly See You

glass gobies masked gobies
A small aggregation of masked gobies (I suspect, based on their masks) stays close to safe shelter on the reef.

THESE LITTLE GUYS ARE SO SMALL AND TRANSLUCENT THAT YOU HARDLY NOTICE THEM, but they’re actually pretty common on reefs in the Caribbean. Tiny fishes that swim in swarms of a dozen or so just off the corals, they’re either glass gobies or masked gobies.

Both an inch or so in length, the two species are so similar that one source suggests the only way to be sure is to hold them in your hand and examine them side-by-side. Sadly, the little guys won’t cooperate.

CONTRADICTORY CLUES

One clue might be in their depth. According to Humann and DeLoach’s Reef Fish Identification Florida, Caribbean, Bahamas, masked gobies (Coryphopterus personatus) tend to hang out in waters between 10 and 35 feet deep, and glass gobies (C. hyalinus) at 40 feet and below. This shot was taken at about 45 feet. Ergo, glass gobies. But Snyderman and Wiseman, in Marine Life, Caribbean, Bahamas, Florida, place the masks’ limit as far down as 90 feet, the glasses’ at 100 and deeper. Re-ergo: Masked gobies.

But, Humann and DeLoach say, they sometimes mix, so it’s not for sure anyway.

Peterson’s Field Guide to Atlantic Coast Fishes suggests a way to tell the difference is the dimensions of their mask, the dark band adorning their snouts. Masked goby masks extend back past the eyes. Magnifying the photo as much as possible yields…coarse pixels. It seems like they sport the extended masks, but it’s hard to tell for sure. Possible ergo, masked gobies.

FINS & LATERAL LINES

Entries in the Encyclopedia of Life tend to focus on describing in detail the little fishes’ markings and the ray-counts in their fins. Glass gobies are supposed to be a brighter orange, masked gobies a paler orange. Since it’s hard to sneak up on them and count, let’s just say they tend to have single rows of white rectangles on each side along their lateral lines. To my eyes their bodies are a sort of translucent orange, blending in well with the reef structure behind them.

glass gobies masked gobies
Whereas, I suspect these are glass gobies, based on their smaller masks.

PROTECTED SWARMS

What is clear is that these little masked/glass gobies are found in aggregations that generally frequent protected alcoves in the coral. Humann and DeLoach describe them in the bottom-dwellers section, although they clearly are free swimmers, perhaps several feet above the bottom. In my observations, they’re always close to a wall.

No one describes them as cleaning gobies. Actually, no one mentions their feeding preferences at all. I infer that they are plankton pickers. And they’re good at evading divers’ attempts to get close to them.

One thing that is clear: They’re found throughout the Caribbean. As for the Indo-Pacific basin, there are a gazillion species of gobies found there, but I haven’t found a reference to anything like my little Caribbean guys.

THE POINT

Does any of this matter? Well, we’re all God’s creatures, great and small. In my view, the smaller ones are often the most interesting.

PRINCIPAL SOURCES: Reef Fish Identification Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Peterson’s Field Guide to Atlantic Coast Fishes, C. Richard Robins, G. Carlton Ray, John Douglass;  Marine Life, Caribbean, Bahamas, Florida, Marty Snyderman & Clay Wiseman;  Coryphopterus personatus, Coryphopterus hyalinus,  Encyclopedia of Life; Coryphopterus personatus, Coryphopterus hyalinus, www.fishbase.in; www.coralreeffish.com.

 

Advertisements