The oyster is one of the important commercial molluscs in Taiwan, and their production and value in 2008 were 34,514 metric tons and NT 3.6 billion dollars, respectively. In the past, the grow-out oyster industry faced the attack of typhoon during summer and fall and the elongation of cultivation duration. So, it is necessary to select the rapid growth oyster strain as the target to cultivate. The present study is focused on the comparison of growth and survival of cultchless oyster reared in the coast and pond to understand the situation of rapid growth oyster reared in the natural environment. Moreover, the oyster spat collection industry in Taiwan were often met with the inconsistent production of natural spat due to typhoon season and the confirmation of the timing of substrate setup. In order to understand the setting condition in the production of artificial oyster cultch, several studies including the effect of larval density on the amount of settled spat, the study of optimal setting period of eyed larvae of oyster, the light condition and the setup of production model were conducted.
The growth in weight of oyster reared in the coast and pond were not significantly different during the four months. But the growth in shell length of oyster reared in the coast were better than those reared in the pond. Because the smaller oysters were eaten by natural predators, such as crabs, the survival of oyster in the coast is lower (38%). This was why the shell height of oyster reared in the coast was higher than those in the pond. In general, oyster in the coast and pond had a tendency that the higher the suspended solids and chlorophyll a were, the less the SPGs were. The decrease of growth of oyster reared in the coast at the final month were related to the abrupt increase of suspended solids and decrease of POM/PIM ratios. The increase in the PIM fraction can dilute the useful POM fraction of suspended solids, thereby decreasing the rate of energy acquisition in bivalves.
The amount of spat on the shell were 0.02±0.005, 0.14±0.02, 0.21±0.04, 0.58±0.16 and 0.86±0.03 ind./cm2, respectively. The amount of spat increased significantly when the larval densities increased (P<0.001).The setting amount of spats on the shell were 0.48±0.17, 0.19±0.06, 0.87±0.20, 1.05±0.33, 1.01±0.20 and 1.00±0.01 ind./cm2, respectively. There were significant difference between six examination time points (P<0.05). Most of eyed larvae finished the settlement during 24 hrs. The amount of setting spat were not significantly different after 24 hrs. It meant it needed only one day to set for the eyed larvae collected by a No.80 mesh net. The higher the light intensity was, the higher the setting rate was in the present study. It is necessary to ascertain further whether the high intensity light enhanced the growth of algae and bacteria in the water. In the production of artificial oyster cultch, it is better and easier to operating outdoors than indoors because the growth of oyster spats is better and the control of algae concentration is easier. The setting number on the shell should be adequate to avoid the competition of barnacles.