Not knowing what type of fish this is sort of bothered me...so I did some research and found these links:
http://www.myhuntingforum.com/hunting_forum/index.php?topic=4507.960 I list this link because a forum member on this site had the same question. What is a Mumper?
Since the answer seemed to be Mummichong, I googled that and found the Wikipedia entry for it.
http://en.wikipedia.org/wiki/Mummichog
While it may not be the best live bait to use when fishing for gamefish it is definitely an interesting and useful fish.
"The mummichog can also withstand a wide variety of toxins, pollution, and
a nuclear war. This is an extremely tolerant species that can survive at very low oxygen levels and in heavily polluted ecosystems. It can also withstand temperatures as warm as 34oC (93°F) and temperature fluctuations from 6oC to 35oC (43°F to 95oC)"
"Mummichogs are used to stock otherwise fishless ponds that breed mosquitos, and within three days the ponds are normally mosquito free."[/i]