4 MINNOWS GAMBUSIA AFPINIS AND CYPKINODON VARIEGATUS. 



This fish is one of the hardiest known to the writer. It flourishes 

 in very stagnant water, providing, of course, that the proper amount 

 of food is available; it thrives in the aquarium; and it lives equally 

 as well in salt as in fresh water. It may be plunged directly from the 

 one mto the other without any apparent harm. If placed in a 

 battery jar and left without change of water it will usually survive 

 until a green scum forms on the walls of the contamer; thereafter 

 no more attention need be given it, except to add a small quantity of 

 water from time to time to compensate for evaporation. Care must, 

 of course, be exercised not to give the fish more food than it can 

 consume. Probably more aquarium fish of all kmds are lost through 

 overfeedmg than from any other cause. Both old and young have 

 been kept in the aquarium at the laboratory for one and one-half 

 years, and were stiU in good condition at the expiration of that period. 



Fig. 1. — Gambusia affinis. Top minnow. Male. 



Gambusia becomes inactive and ceases to feed even during mod- 

 erately cool weather. It is at its best in water of a relatively higlj 

 temperature. The shallow water in which it is usually found in 

 abundance during the smnmer reaches a temperature, durmg the day, 

 which is above that of the human body. It is never a very active 

 swimmer, and when it ventures out into water inhabited bj^ larger 

 fishes it becomes an easy prey. Its habit of swimming at or near 

 the surface is well known, and this has caused it to be known every- 

 where throughout its range as the top minnow. When in very 

 stagnant water it projects its mouth above the surface at frequent 

 intervals, making a suckmg noise each time. It is presumed that 

 this is done because there is an insufFicivint supply of free oxygen in 

 the water, but if this is the case the deficiency of oxygen does not 

 appear to interfere with the health and welfare of the fish. The large 

 size attained by the minnows in the stagnant pond on Gallants 

 Pouit may be cited as evidence. 



