In this study we describe spawning induction, fecundity estimation, and the early life history of the rock scallop Spondylus calcifer under laboratory conditions. We collected adults of S. calcifer from a natural stock in the Gulf of California, Mexico (28°37′N, 112°15′W). We induced spawning by means of thermal shocks (10°C magnitude) and estimated species fecundity as a function of size. We evaluated the effects on growth rate and final survival of larvae reared with 3 dietary treatments: (1) 30 cells/µL, (2) 50 cells/µL, and (3) 75 cells/µL. We reared larvae in 15-L containers at a density of 3 larvae/mL at 30°C, and renewed 100% of the water culture every 48 h. The diet comprised a combination (1:1) of Isochrysis galbana (clone T-ISO) and Chaetoceros calcitrans (clone C-CAL). Both females and males responded positively to thermal shock induction. Mean size of oocytes was 56.0 ± 4.2 µm (standard deviation; n = 30). Mean number of oocytes spawned was 48.9 × 106 ± 13.2 × 106 with the smallest female (shell height, 110.5 mm) spawning 28.95 × 106 oocytes and the largest (shell height, 180 mm), 71.76 × 106 oocytes. We observed the first group of throchophore and D-larvae at 7 h and 17 h after fertilization, respectively. At the beginning of the experiment, the mean shell height of D-larvae was 79.8 ± 8.54 µm (n = 35). Two weeks after fertilization, larvae reached the pediveliger stage and we ended the experiment. We found that S. calcifer larval growth rates were significantly different between diet treatments (F2.2.703 = 24.65; P < 0.001), with larvae reared at 50 cells/µL exhibiting the highest growth rate (12.42 µm/day) of all treatments. At the end of the experiment, larvae fed at 50 cells/µL attained a larger size (mean height, 234.01 ± 28.03 µm; n =115) than larvae from the other 2 treatments (30 cells/µL: mean height, 210.48 ± 30.81 µm; n = 107; 70 cells/µL: mean height, 221.81 ± 29.81 µm; n = 104). We did not find significant differences in larval survival between diet treatments at the end of the experiment (F2.6 = 0.63; P = 0.56). Our findings suggest that the minimum period for larvae of S. calcifer to begin settlement is approximately 15 days after fertilization under the experimental conditions assessed. The first appearance and the extension of the planktonic stage represent the minimum extension that the larvae can be subject to dispersion by oceanographic currents. Whether S. calcifer can delay settlement if no suitable substrate is found was not addressed in this study. These results will be used as an input for the development of a coupled biological—oceanographic model that can assist in management of the rock scallop fishery in the Gulf of California by predicting species larval dispersion patterns from known reproductive sources.
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Vol. 29 • No. 1