DRIED-ALGAE DIETS AND INDOOR NURSERY CULTIVATION OF MANILA CLAM JUVENILES

Manila clam (Tapes philippinarum Adams and Reeve) juveniles were grown in experimental (50-litre) and commercial (1000-litre) scale recirculating seawater upwelling systems. Growth was better with a mixed diet of spray-dried Tetraselmis suecica (Kylin) Butch. and a live diatom, Skeletonema costatum (Grev.) Cleve, than with either component fed singly. Juveniles fed a mixture in the ratio (by dry weight) of 70% spray-dried T. suecica and 30% live S. costatum showed similar growth as animals fed the same proportions of an all-live algal diet. Using the spray-dried/live algal mixture, a ration of 0.4 g (dry weight of food) per g (initial live weight biomass of juveniles) per week gave slightly better growth, but was utilised much less efficiently, than a ration of 0.2 g g-1 week-1. For both food rations growth rates of clams decreased when live weight biomass of juveniles in the up-welling systems at the beginning of each week was increased from a stocking density of 0.04 g/l to 0.3 g/l.