Abstract

Supply of proper microalgae is very critical because it determines total production and cost of larval Ark shell, Scapharca broughtonii during larval development stages. Besides, nutrient requirements of microalgae should be carefully determined for successful larval Ark shell production. In order to improve utilization of microalgae being used for artificial Ark shell seed production and optimum larval growth of Ark shell, growth and survival (%) of larvae on development stage of Scapharca broughtonii fed on four different microalgal species (Isochrysis galbana, Pavlova lutheri and Chaetoceros simplex, Tetraselmis tetrathele) were investigated. In D shape stage the larvae fed on mixed diet with four microalgal species showed the highest growth in shell length ($129.6{\pm}5.7{\mu}m$) and survival ($84.2{\pm}5.8%$) (P < 0.05). The growth and survival (%) of the larvae fed on mixed diet with two microalgal species of P. lutheri + C. simplex were lower than mixed diet with four microalgal species and significantly higher than other mixed diet with two microalgal species (P < 0.05). Such change in the growth and survival of larvae fed on different microalgal species varies with larval development stages although a similar tendency on the growth, daily increment of shell length and survival in D shape, early umbone, umbone and late umbone stages were observed. In D shape stage the larvae fed on the feeding concentration ($2{\times}10^4cells/mL/day$) of mixed diet with four microalgal species showed the highest growth in shell length ($125.8{\pm}5.1{\mu}m$) and the feeding concentration ($1{\times}10^4cells/mL/day$) of mixed diet showed the highest survival ($88.3{\pm}4.9%$) (P < 0.05). The growth of larvae tended to be higher, the higher the feeding concentration of diet but the lower survival of larvae showed, the higher feeding concentration of diet. Such change in the growth and survival of larvae fed on concentrations of mixed diet with four microalgal species varies with larval development stages although a similar tendency on the growth, daily increment of shell length and survival in D shape, early umbone, umbone and late umbone stages were observed. Daily feeding concentrations of $1{\times}10^4-2{\times}10^4cells/mL$ of microalgae mixed two species including C. simplex were very effective.