Suspension culture of catarina scallop Argopecten ventricosus (=circularis) (Sowerby II, 1842), in Bahia Magdalena, Mexico, at different densities

Hatchery-reared spat (5 mm) of catarina scallop (Argopecten ventricosus (= circularis)) were cultured in plastic trays suspended from a long line at Rancho Bueno, Baja California Sur, Mexico. The mean surface temperature range was 20 to 29 degrees C and salinity remained steady at 37 ppt during the 320-day experiment. Every 1 or 2 months, the trays and the scallops were cleaned, the scallops measured, and survival recorded. Three densities were tested on each of the culture stages; called nursery (from day 1 to day 80), intermediate (80 to 136) and growout (136 to 320). Average densities were 1500, 2500, and 4000 scallops/m(2) for the nursery stage; 400, 700, and 1000 for the intermediate; and 150, 250, and 400 for the growout stages. At the end of nursery and intermediate stages, scallops of the modal size class were selected to begin the following stage using scallops of homogeneous size. In the nursery stage, growth rate was higher at low density. At the intermediate stage, growth rates were highest in low and medium densities (P < 0.05). Growth rates were the same at low and medium densities in the growout stage. Muscle weight was affected by density (P < 0.05) on scallops of similar size from different densities at the end of the experiment. Scallops cultured at low density have more muscle weight than those cultured at high density. Survival was > 91% at the end of the experiment and did not correlate with density. Mortality began to occur in animals older than 8 months, during the spawning season at the onset of summer. Two hypothetical growth curves were constructed from the data taking for each stage those densities producing the fastest and slowest growth. Results indicate maximum shell length could be attained in 273 (fastest) and 398 (slowest) days. A cost analysis indicates that, regardless of the longer time, culturing scallops at high density would be less expensive than at low density, taking into account the muscle-weight loss caused by crowding. (C) 1997 Elsevier Science B.V.