FISHES OF THE GULF OF MAINE 157 



edges of anals and ventrals are yellow. Sometimes there is a dark-edged, pale- 

 centered eyespot on the rear part of the dorsal fin. At spawning time the pig- 

 mentation of the male is generally intensified, the back and upper sides darkening 

 almost to black, while the yellow of the belly becomes more brilliant and the body 

 generally assumes steel-blue reflections. The females (much paler than the males) 

 are uniform olive to bottle green, darker above, lighter below, without definite 

 markings though their sides often show faint and indefinite crossbars of a deeper 

 tone of the same hue. Their fins are much paler than those of males. Very young 

 fry of both sexes show dark transverse bars on the sides but these are lost with 

 growth. 



Killifishes, as is well known, vary in shade from very pale to dark, according 

 to the color of their surroundings, and recent experiments *' have proved that 

 their ability to change from light to dark depends on the sense of sight. 



Size. — The maximum length is 5 to 6 inches, but adult mummichogs are seldom 

 more than 3 or 4 inches long in the Gulf of Maine. Several varieties of this species 

 have been described, but they are so closely allied that it is not necessary to discuss 

 them here. 



General range. — Coast of North America, from the Gulf of St. Lawrence to 

 Texas. 



Occxirrence in the Gulf of Maine. — The mummichog is very abundant in suitable 

 locations all around the shores of the Gulf of Maine. However, it seldom if ever 

 ventures into the open sea, for its home is along sheltered sandy beaches, especially 

 where the tide flows over beds of eelgrass or among beds of salt hay (Spartina), 

 among which shoals of "mummies" may often be seen moving in with the flood 

 tide. They also swarm in the tidal creeks that cut up the salt marshes, on the 

 shores of our harbors, and in the brackish water at the mouths of our streams and 

 estuaries, particularly in little muddy pools, creeks, and ditches. So closely, in- 

 deed, do they hug the shore that aline drawn 100 yards out from land would probably 

 inclose 90 per cent of all the mummichogs in the Gulf of Maine. Wliere the shore 

 is bold and rocky, as about the Bay of Fundy, the mummichog is practically re- 

 stricted to brackish water, and often goes up into fresh water. It is not likely that 

 it ever descends to a depth of more than 2 or 3 fathoms in its journeys in and out 

 of the creeks or up and down the shore. It is so resistant to a lack of oxygen, the 

 presence of carbondioxide, and unfavorable surroundings generally, that it can 

 survive in very foul water. 



Habits. — ^The mummichog winters in a more or less torpid or at least sluggish 

 state on the bottoms of the deep muddy holes or creeks. We have no evidence 

 that it goes to sea during the cold season any more than in summer, and in general 

 it is one of the most stationary of fishes. At ebb tide "mummies" are often trapped 

 in little pools where they remain until the next tide if the water holds, often huddled 

 together in swarms. Should the pool go dry, however, they work their way into 

 the mud for the time being, where we have often found them, and probably they can 

 flop overland for a few yards to some other drain as the striped mummichog does.^^ 



" Parker and Lanchner. American Journal of Physiology, Vol. LXI, 1922, p. 548. 



" This habit is described by Mast (Journal of Animal Behavior, vol. 5, No. S, 1915, p. 341-350). 



