Prateep Songkeao, Sommai Chiayvareesajja, and Saowapa Angsupanich

pp. 621 - 631

Abstract

This study examined the effect of using oysters (Crassostrea belcheri Sowerby) to treat effluent
resulting from the intensive culture of black tiger shrimps (Penaeus monodon Fabricius) at the Marine
Shrimp Research and Development Center, Songkhla Province. There were 8 treatments - 0 (control), 10,
20, 30, 40, 50, 60 and 70 g oysters/l, with 3 replicates. The oysters, weighing 25±5 g each with a mean shell
length of 5.2 cm, were placed in 30 × 60 × 30 cm-glass aquaria and placed outdoors with a static water system
(no water exchange, but aeration provided throughout the experiment). Water quality was monitored for
chlorophyll a, total ammonia nitrogen (TAN), nitrate, nitrite, phosphate, total suspended solids (TSS), BOD, salinity and temperature before adding the oysters and at 1, 2, 4, 6, 8, 10 and 16 days afterward.
It was found that the correlation coefficients between oyster density and concentrations of chlorophyll a,
TSS and BOD were negative, but positive for the correlation between oyster density and TAN. Thirty g
oyster/l at 4 days was the most efficient treatment based on the percentage decrease of chlorophyll a, TAN,
TSS and BOD (86.54%, 15.56%, 47.26% and 79.35%, respectively), all of which values are in acceptable
safety ranges for aquatic animals. With treatments longer than 4 days, or densities over 30 g oyster/l,
the TAN concentration increased with time and BOD exceeded the safety standard. At 70 g oyster/l, the
oyster mortality was greater than 10% after 16 days of the experiment, at which time the experiment was
terminated.