4) How do the deep water anglerfish locate their prey in darkness?
The anglerfish has a long fishing-rod-like adaptation protruding from its face, on the end of which is a bioluminescent piece of skin that wriggles like a worm which attracts preys in the dark. The anglerfish will wait for the prey to come near the light then gobble it up.
5) Why can’t a saltwater fish survive in freshwater aquarium? What are the differences in pH between seawater and freshwater ponds
Saltwater fish are adapted to living in salt water, dealing with water constantly rushing out of their bodies, and excreting concentrated amounts of salt. When placed in freshwater, the fish will continue to excrete as much salt as before, causing it to lose too much salt from their body and die.
Freshwater fish are adapted to absorbing more salt from their surroundings to replace the salt they excreted, so they will have too much salt in their body and die.
Only a few species of fish can live in both saltwater and freshwater, and one such example is the salmon
Sources: http://www.frogfish.ch/deepsea-anglerfish.html, http://en.wikipedia.org/wiki/Deep_sea_fish, http://en.allexperts.com/q/Biology-664/Fish.htm, http://wiki.answers.com/Q/Why_can%27t_salt_water_fish_live_in_fresh_water,