Feeding, Reconditioning, and Rematuration Responses of Captive Atlantic Salmon (Salmo salar) Kelt

Wild Atlantic salmon (Salmo salar) kelt were reconditioned in the laboratory by initiating their feeding during the winter on freshly thawed Atlantic silverside (Menidia menidia) supplemented with vitamins and trace minerals. Some kelt improved in condition by April, and by June the majority were reconditioned. Some females skipped a year of reproductive activity with most rematuring a second time the following year. One group of females rematured and was spawned a third time without skipping another reproductive cycle. Plasma levels of vitellogenin, estradiol, and testosterone remained low in reproductively inactive female kelt; in contrast, these substances increased and peaked just prior to spawning in late October in maturing female kelt. In males, plasma levels of testosterone and 11-ketotestosterone rose in conjunction with testicular development, reaching peak hormone values during the period of spermiation. Although good-quality eggs were collected from reconditioned kelt according to high egg fertilization rates and high rates of egg survival through the eyed and hatching stages, most kelt yolksac larvae died just prior to swim-up. High mortality rates for kelt larvae suggest that either the silverside diet is nutritionally deficient or that the physiology of reconditioned kelt broodstock is inadequate for good-quality egg production.