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In 2003 the Thailand authorities deliberately sank a Chinese fishing vessel
off Similan Island number five in order to create an artificial reef.
The wreck later became commonly known as the "tuna wreck".
Just a few months after the sinking,
the wreck had already become home to quite a variety of marine life.
In particular, shoals of tiny cardinalfish
were already swarming in and around the wheelhouse.
Cardinalfish also find shelter in this small wreck on Racha Yai's Home Run.
Many of the Andaman's natural reefs
are similarly cloaked in shoals of tiny fish.
These luminous cardinalfish shelter amongst black sun corals.
Here at Koh Bida Nai the whole reef appears to sway with life.
While a social aggregation of fishes is known as a "shoal",
when they are more tightly organized and swim with coordinated movements,
they are known as a "school".
The tendency of fishes to form schools is a natural defense mechanism.
Each fish instinctively follows its neighbours' movements very closely,
and the resulting congregation can be confusing for predators.
The sheer number of eyes in a large school
makes it easier for the fish to spot predators.
It's all about strength in numbers.
Schooling fishes tend to choose other fishes of similar size and appearance,
but not always the same species.
If a fish stands out, it is more likely to be targeted.
This African pompano at Shark Cave made some half-hearted attempts
at catching the schools of fusilier and young barracuda.
On this occasion it left empty-mouthed.
Striped eel catfish such as these at Lucy's Reef
are invariably found in schools.
They forage for food in the day,
but are seen here resting at night.
Bigeye snappers can be seen schooling at Hin Muang.
Enormous schools of these fish are a feature of many reefs.
Bluestripe snappers form slightly smaller schools,
as do their cousins, two-spot banded snappers.
Variable-lined fusiliers, a common sight in the Similans,
often gather in their thousands,
and more often than not they're all swimming in the same direction.
The Andaman Sea is home to several species of schooling barracuda.
Large schools of bigeye barracuda are common at more inshore sites
such as the Racha Islands.
At Black Rock the larger pickhandle barracuda,
with it's distinctive yellow tail, is a common sight.
At Koh Tachai and Richelieu Rock you are more likely to find blackfin barracuda.
In the Mergui Archipelago, the similar but smaller sawtooth barracuda is more common.
At Western Rocky Island the school sometimes forms a huge vortex.
Like barracuda, dogtooth tuna prefer to socialize and hunt in numbers.
Of the trevally family, it's most likely bigeye trevallies
that form large schools in their search for small reef fishes.
Again, isolated outcrops such as Richelieu Rock and Black Rock
provide the upwellings and currents that the trevally favor.
While forming schools can provide a degree of protection for some fishes,
others will take a more direct approach to survival.