Kelvin K P Lim and Jeffrey K Y Low
The frogfishes (family Antennariidae) go one step further. Not only does a frogfish resemble a piece of sponge, it also has a little bushy filament attached to the top of its snout. It waves this about to attract passing fish which may mistake it for some zooplanktonic titbit. When a fish lunges for the lure, it immediately disappears into the large gaping mouth of the patient predator.
Fishes which lack the appearance of their substrate may seek to hide behind some harmless-looking object to get closer to their prey, somewhat like a wolf in sheep's clothing. The flathead gudgeon (Butis butis) can sometimes be found lurking under drifting dead leaves in an upside-down position. From this hide-out, it is thus able to pounce on unsuspecting small fish or shrimps.
The archerfishes (Toxotes spp.) have their mouths adapted for shooting jets of water into the air rather like a water pistol. Using this device, coupled with its keen eyesight, an archerfish is able to knock down an insect on an overhanging twig with a jet of water from below. The insect is immediately pounced on when it falls into the water.
There are fishes which mimic poisonous creatures to avoid being eaten. The juvenile clown sweetlips (Plectorhinchus chaetodonoides) not only seems to attempt to look like some poisonous flatworm, but also tries to swim like one with undulating motions. The false scorpionfish (Centrogenys vaigiensis) strongly resembles members of the scorpionfish family, but lacks their venomous spines.
Chemical defence is used by some fishes to deter predators. The yellow soapfish (Diploprion bifasciatum) and the shortnose boxfish (Rhynchostracion nasus) secrete toxic mucus when severely harassed. In the open sea, this probably serves only to irritate, but in an enclosed space like a rock pool or an aquarium, it could kill all the inhabitants, including the soapfish and boxfish themselves. The peacock sole (Pardachirus pavoninus) produces a toxin which is known to repel sharks.
The porcupinefishes (family Diodontidae) have a formidable array of sharp spines (actually modified scales). Normally these lie flat against the body until the fish is harassed by a large fish or human diver. The porcupinefish then rapidly sucks in water to inflate its body into a ball. The spines are thus erected and these protect the fish from being swallowed or injured by its attacker.
The butterflyfishes Chelmon rostratus and Parachaetodon ocellatus have a large spot on the soft dorsal fin. These spots are said to resemble eyes while the real eyes are concealed by a stripe over the head. It seems that the so-called eye-spot serves to confuse predators by focusing their attention on the rear part of the body rather than on the head. Similarly, the eight-banded butterflyfish (Chaetodon octofasciatus) also confuses predators with its pattern of narrow dark bands. It can be difficult to tell head from tail at a distance.
The electric ray (e.g., Temera hardwickii) has two gelatinous electric organs at the base of its eyes. This normally inoffensive fish can generate enough electricity to jolt an adult human if it is touched. Otherwise the device appears to be used mainly for detecting and immobilising prey or for finding its way around.
Coastal Marine Habitats
Fishes and Man
About the guidebook
From A Guide to Common Marine Fishes of Singapore by Kelvin K P Lim and Jeffrey K Y Low
Published by the Singapore Science Centre and sponsored by BP
©Raffles Museum of Biodiversity Research and Singapore Science Centre