Recent research has revealed that alewives may also be affecting gamefish in adverse ways. Alewives are known to feed aggressively on the fry on some native species, including lake trout and yellow perch. Alewives contain high concentrations of an enzyme that breaks down thiamine, which, when liberated during digestion in the gut of a predator, destroys thiamine from the meal before it can be absorbed. Adult fish move from deep water to shallow water areas near beaches in lakes or in ponds over sandy or gravelly bottoms. Eggs are scattered at random and then abandoned.
Young alewives eat zooplankton, adding insect larvae to their diets as they mature.
Alewife populations typically undergo extreme fluctuations in their numbers. During some years, Lake Ontario alewife populations have suffered large die-offs. Because of the problems associated with these population fluctuations, DEC and the Ontario Ministry of Natural Resources have adjusted stocking levels of trout and salmon to avoid an imbalance between the supply of alewives and their prey. The rainbow smelt is a slender, elongated, pale fish that averages seven to eight inches in length. A distant relative of trout, salmon and whitefish, it has a greenish back and silvery sides with a bright silver stripe and brown or black spots.