There is an explanation about salmon fry which has them gradually going seaward in order to escape the brighter light in the shallow fresh waters; but is there anything in the constitution of an alewife that is not accustomed to sunlit waters? They do not escape them so much as seek them, because of their warmer temperature. Aside from that, I would think, from my own observation, and the comments of others, that they have no preference between the dark and light along their way--they run through both--but do not like a sudden change. For example, they waited all one morning before coming out of the shaded waters under Stony Brook Road to go into the brightness of the seining pool, only moving when a shadow fell across it that was cast by the old mill. If the adults swim toward the coast in the spring because of some change in their make-up consonant with changes in the waters where they swim, is there also some change in food and temperature which makes the young start to leave fresh water at a particular time? The little alewives are creatures of such sensitivity to their medium, to its changes, and to what they eat, that a factor in the timing of their migration might be some internal discomfort, or so it was suggested to me. To begin to find out, a scientist would have to follow all the stages of a little alewife’s birth and growth, tracing where it goes, what it eats, and what the temperature, depth, and density of the water is along the way. He would also have to do this for every age group that leaves the three ponds from July through October, analyzed pond by pond, since conditions differ in each one. During this period the little fish leave at all stages in the seasonal development of the ponds, while not all of one age group seem to go with the others. Many appear to stay in the ponds for several months. So attempting consistency with such findings might result in more indigestion for the investigator than the fish themselves. From the outward evidence all I can say is that these little ones do not start schooling to move out of the ponds until they are over an inch in length. I have seen them, still not much more than pin size, circling a few hundred yards above the outlet, but neither swimming with the flow nor letting themselves be drifted on. Logically then, the point at which they are stimulated to leave must coincide with growth, the rate of which depends on food and temperature in the ponds. Warm-water ponds are more favorable to growth than cold-water ponds. They turn out better fish, larger and healthier. By the same token a cold spring and summer will result in a poorer crop of alewives. They will probably be hatched later. The colder pond waters will bring down the “plankton bloom,” in other words less food for the fish. As a result, young alewives going to salt water that year will be smaller, weaker, more subject to disease, and less able to escape their enemies.