Waste excretion characteristics of Manila clams (Tapes philippinarum) under different temperature conditions.
Water recirculating systems have been used in the shellfish industry for depuration and wet-storage. Knowledge of shellfish excretion characteristics is critical to recirculating system design. In this study, the excretion rate of total ammonia nitrogen (TAN), total Kjeldahl nitrogen (TKN), and 5-day biochemical oxygen demand (BOD5) from Manila clams (T. philippinarum) were investigated under laboratory and commercial conditions. The laboratory tests were conducted under temperatures ranging from 3 to 30°C. The experimental results showed that temperature was a key factor in determining the excretion rate of all the above parameters. The relationship between TAN excretion rate (RTAN) and temperature (T) can be represented by an exponential function (RTAN = 0.57×1.25T). For the temperature range between 3 and 20°, the daily mean excretion rates of TAN, TKN and BOD5 ranged between 1.5-46.1, 4.8-131.0 and 57.4-219.4 mg/kg of clams (wet weight with shell on), respectively. There were linear correlations between TAN, TKN and BOD5 production rates. The data presented can be used to estimate waste generation from a given shellfish processing operation and to size the waste treatment components for a recirculating depuration (or wet-storage) system.