Influence of food supply on postmetamorphic growth and survival of hatchery-produced lion's paw scallop, nodipecten nodosus

Poor growth and low survival are often reported in hatchery-reared scallops early after settlement and metamorphosis. The effects of algal deprivation, substrate biofilm, and two algal cell concentrations (ca. 4.7 x 10 super(3) and 4 x 10 super(4) cells mL super(-1)) on growth and survival were investigated during 9 days after settlement in experiment 1, and the effects of the two algal concentrations were examined for 16 days post-set in experiment 2. In experiment 1, the presence of a biofilm on the collectors significantly enhanced postlarval settlement, but not growth. Five days after settlement, at a shell height of about 250 mu m, postlarvae fed a low algal concentration were significantly larger than postlarvae in the other treatments (unfed, biofilm-covered collectors and high algal concentration), which attained similar sizes. Nine days post-set, postlarvae fed at higher algal concentration were larger than postlarvae to which no suspended algae were supplied but were smaller than those cultured at low food concentration. Reserves accumulated during the larval stage were sufficient to sustain metamorphosis, limited shell growth, and high survival in the absence of exogenous food, giving no indications of food deprivation-induced mortality for at least 9 days post-set. In experiment 2, 10 days after settlement, postlarvae cultured at 4.7 x 10 super(3) cells mL super(-1) were larger than postlarvae cultured at 4 x 10 super(4) cells mL super(-1), but after 16 days post-set, postlarvae in both treatments attained similar shell height. Between 10 and 16 days after settlement (shell height ca. 300-400 mu m), feeding demand of postlarval Nodipecten nodosus significantly increased, as demonstrated by a sharp increase of gut pigment concentration, which was probably related to key events in the gill morphogenesis. Mortality, on the contrary, was higher at 4 x 10 super(4) cells mL super(-1) than at 4.7 x 10 super(3) cells mL super(-1). An alternative explanation to the high mortality of scallops often recorded early after metamorphosis in aquaculture settings, other than the depletion of endogenous reserves, is proposed. Food demand of postlarval N. nodosus is less than usually supplied in scallop hatcheries, and growth can be significantly increased early after settlement by adjusting the algal cell concentration.