Answer to Question 1True
Answer to Question 2Competitive pressure among the large number of fish species has given rise to a variety of
feeding and defense tactics. Sight is very important to most fishes, enabling them to see their
prey or avoid being eaten. Even some deepwater fishes that live below the photic zone have
excellent eyesight for seeing luminous cues from potential mates or meals. Hearing is also well developed, as is the ability to detect low-frequency vibrations. The bizarre flattened
crossbar of the hammerhead shark may provide a kind of stereo smell to sense differing
amounts of interesting substances in the water. Salmon smell their way to their home streams
after years at sea by detecting faint chemical traces characteristic of the water from the
stream in which they hatched. About a quarter of all bony fish species exhibit schooling
behavior at some time during their life cycle. A fish school is a massed group of individuals
of a single species and size class packed closely together and moving as a unit. Schools have
the added benefits of reducing chance detection by a predator, providing ready mates at the
appropriate time, and increasing feeding efficiency. Fishes living in the twilight world at the
bottom of the photic zone use bioluminescence in feeding, avoiding being eaten, and mate
attraction. Some members of this sparsely populated community have built-in luminescent
organs that cast dim blue light downward; this light masks their own shadows, so they have
less chance of being detected and eaten. Other deep-swimming organisms attract their
infrequent meals with a luminous lure. Some use flashes of light to dazzle or frighten
potential predators.
Spinnbarkeit is the ability of cervical mucus to stretch a distance before breaking.
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