養殖砂蝦水質基準之研究

Abstract

近年來，河川重金屬及農藥污染、養殖環境惡化和疾病等問題，使野生及養殖砂蝦的產量下降。砂蝦肉質甜美且耐乾力强，為經濟蝦種及環境監測的敏感生物，因此探討砂蝦對溫度、鹽度、pH的耐受度，及重金屬鉛和4種農藥對砂蝦之毒性大小與急、慢性毒效應，並配合以往之文獻資料，求出砂蝦最適生長環境條件及生物安全濃度，以此做為了解汙染危害、建立砂蝦養殖水質基準之依據。急性試驗方面，於15、25、35 ℃下，設置不同鹽度、pH值、鉛、靈丹、甲基巴拉松、巴拉刈和丁基拉草濃度等處理，計算半致死濃度(LC50)；慢性試驗方面，於15、25 ℃下，比較不同處理間的砂蝦成長量。結果發現砂蝦最適生長環境：水溫23 ~ 30 ℃；鹽度15 ~ 25 ‰；pH 7.0 ~ 8.5。五種重金屬對砂蝦之生物安全濃度：汞0.007 mg/L、鉛0.025 mg/L、鎘0.05 mg/L、銅0.15 mg/L、鋅0.2 mg/L。農藥方面，96 hr LC50值為丁基拉草＞巴拉刈＞甲基巴拉松＞靈丹，隨暴露時間增加而降低，其安全濃度分別為0.03 mg/L、＜0.01 mg/L、0.001 mg/L、0.0004 mg/L；同處理的25 ℃之96 hr LC50皆比15 ℃、35 ℃高。氨氮與亞硝酸鹽則分別訂為0.02 mg/L、1.9 mg/L。這些因子如鹽度、pH、鉛、甲基巴拉松、靈丹、巴拉刈和丁基拉草都會抑制砂蝦成長，減少砂蝦攝食量，提高其死亡率；ㄧ般而言，農藥毒害比重金屬較大，且毒性因水溫而異；25 ℃時，砂蝦對農藥耐受度較高，因此在養殖或取用養殖用水時，應嚴格管制毒物及廢棄物排放，減低農藥及重金屬污染對砂蝦的危害，才能增加砂蝦養殖的安全性。

In recent years, due to water pollution, environmental deterioration and disease outbreak, the production of sand shrimp (Metapenaeus ensis) has decreased markedly. This shrimp is an economical and sensitive species for environmental monitoring, so we study the tolerance levels of sand shrimp with temperature, salinity, pH, heavy metal lead and four kinds of agriculture chemicals. The purpose of this study is to compare their toxicities by means of optimal growth condition and try to find out the biologically safe concentration for setting up its water quality criteria. Acute toxicity and chronic effects were carried out at 15 ℃ and 25 ℃. Results indicated that the optimal growth condition were in the ranges of water temperature 23 ~ 30 ℃, salinity 15 ~ 25 ‰, pH 7.0 ~ 8.5. The safe concentrations of five kinds of heavy metals for sand shrimp are 0.007 mg/L mercury, 0.025 mg/L lead, 0.05 mg/L cadmium, 0.15 mg/L copper, 0.2 mg/L zinc. For agriculture chemicals, the 96 hr LC50 differs significantly, with butachlor＞paraquat＞parathion-methyl＞lindane, and the safe concentrations are 0.03,＜0.01, 0.001 and 0.0004 (mg/L) respectively. Unionized ammonia is more toxic than nitrite, being with 96 hr LC50 of 0.02 and 1.9 (mg/L) separately. Low salinity, extreme pH and high concentrations of lead, lindane, paraquat, methyl-parathion and butachlor all can inhibit the growth, reduce food consumption and increase the mortality of sand shrimp. In general, the toxicity of agriculture chemicals varied with water temperature and is higher than that of heavy metals, when raised at 25 ℃. In shrimp aquaculture, water qualities have to be maintained at lower concentration of agriculture chemicals and heavy metals, therefore, it needs constantly monitor and controll according to water quality criteria for promoting the production of sand shrimp.