Underwater Life: The last thing a glass fish sees

Shards of living glass

Dive any reef or wreck in Colombo and you will see them.


Small shoals of shining glass fish, shining that is when the light hits them. They blink in and out of existence as the light hits them for a kaleidoscopic experience that is sometimes unreal, especially when they congregate in a huge shoal that engulfs you and surrounds you in small shards of sunlight.

Glass fish on a reef

Glass fish and cardinal fish on the Cargo wreck

Usually the glass fish aren’t so spectacular, they hang around in a group of about a dozen close to any sort of crevasse on the reef or ‘caves’ formed on wrecks by the structure of the sunken ship. Presumably they do this for shelter with a place to retreat to if a predator attacks.

What they don’t seem to realize is that their shelter is most often where the attack is launched from. You don’t have to look too closely at the crevacess and cracks to see them. The groupers lie there innocuously, seemingly somnambulant. Blue line groupers are the most commonly seen though flower groupers and a few others are also relatively common, lounging about warily eyeing you as you pass over their heads. Occasionally one will lose its nerve when you come too close and flash into the depths of the reef, showing remarkable acceleration for what seemed like a sleepy fish.

Nonchalant blue line grouper

It is this acceleration that is the glass fishes’ undoing.

The grouper’s tried and tested fishing method is to lie motionless apparently completely ignorant of the flashing glass fish above its head until the small fish, lulled into a sense of complacency drop their guard.

A millisecond later and the shoal is one less.

Still nonchalant...sort of

If you are lucky and patient, you would have seen the grouper metamorphoses from a motionless fish to a blurry missile, mouth gaping as the ambush is sprung. A flurry of activity ensues as the glass fish swirl in confusion and the grouper returns to its post.

Eyeing a target

Peace returns to the reef as the as the glass fish, not blessed with a long memory, forget the ever present danger in the dark.

The last thing a glass fish sees

Hitting the Shoal

One of my favourite spectacles underwater are the ‘bait balls,’ conglomerations of small fish grouping together, tightly packed for protection from predators. These are especially common on the Cargo Wreck where thousands of fusiliers (Caesionidae) can be seen often in amorphous fluidity.

Not exactly a bait ball, but a shoal of fusiliers heading past.

Close up they are quite a beautiful fish

They are especially prolific when there’s a bit of a current and some plankton in the water and while fascinating to watch by themselves, the action really starts when a few Bonito show up. These medium size tuna hunt in small packs of five to eight fish and are capable of simply jaw-dropping bursts of speed.

There is nothing that can compare to the adrenaline rush you get watching these in action. I’d only seen these fish dead on a block of ice at a supermarket before I started diving so the speed and agility which these fish displayed was mind-blowing (I’m of course rapidly running out of superlatives to describe the action). You first notice them as a faint silver streak out of the deep blue. If they pass overhead you can see their slim silhouettes black against the backdrop of the sun glittering through 30 meters of water. You can see them flex their fins, moving them in and out as if warming them up for the rush into the shoal.

You have to keep a close eye on them at this time because even if you look away for a second, you can miss the lightning attack. From almost a standing start, they seem to pick a target and dart into the shoal of fusiliers, a blur as your eye struggles to follow. The bonito arrow is followed by the shoal of fusiliers splitting to avoid the attack, the fish moving as if with one mind. One bonito after another darts into the shoal, the fusiliers desperately trying to avoid the incoming fish. An underwater ballet unfolds that is beautiful to watch but deadly serious. Flashes of tuna and clouds of fusiliers playing a game of life and death, slowest one loses.

(Unfortunately my camera is too crap to capture these images but if you click here, you can see some baitball images that DJ has taken.)

This fusilier obviously caught the wrong end of someone's stick

Whenever I see shoals of fusiliers over the Cargo I always hang around in the water watching them while the uninitiated remain too busy looking at the ship to notice the hunters approaching. One of the seminal moments of the last season was when I was amidships close to one of the masts by myself as the hunters circled. A bonito came tearing into the fusiliers right at me, missed his kill and arched up past my bubbles back into the blue.

A grace under water that has truly to be seen to be believed.