EFFECTS OF A DELAYED-ONSET OF PISCIVORY ON THE SIZE OF AGE-0 BLUEFISH

Variation in advection or other physical forces may accelerate or dela y arrival of young marine fishes into productive nearshore habitats, t hereby affecting the length of the available growing season. The bluef ish Pomatomus saltatrix is an oceanic spawner whose juvenile stages, u pon entry into estuarine waters, become piscivorous and thereby experi ence greatly increased growth. Size attained during the growing season may therefore be determined by time of arrival into estuarine habitat s. We exposed bluefish recently recruited to an estuary to three diet shift treatments in which test fish were fed adult brine shrimp Artemi a sp. for 0, 10, or 20 d before they were switched to piscine prey. Bl uefish that had a delayed onset of piscivory were smaller after 40 d o f growth, indicating that they did not fully compensate for prior peri ods of slow growth. These bluefish did exhibit immediate moderate grow th compensation (about 6% over 10 d) resulting from increased consumpt ion rates, but relatively low growth efficiencies prevented full recov ery of their growth losses. Low growth efficiencies may have resulted from an induced developmental handicap or an energetic penalty for pro longed feeding on an Anemia diet. The timing of age-0 bluefish recruit ment into estuarine environments can have a lasting influence on size attained during the first growing season.