砂蝦於魚蝦混養池的成長、不同蛋白質含量之商業飼料對其成長以及鹽度對其生理影響

Abstract

砂蝦（M. ensis）是臺灣西南部與虱目魚（C. chanos）混養的重要經濟蝦種。受到惡化的養殖環境和病原菌的肆虐，所以在收穫上呈現極大的不穩定。要提高砂蝦產量到符合經濟效益的養殖收成，了解其喜好之生長環境和適宜之飼料是必要的工作。本篇分三部分研究：（1）固定時間到台南縣調查虱目魚和砂蝦混養時的水質變化，並觀察砂蝦生長情形；（2）比較四種商業飼料（斑節蝦、草蝦、白蝦和虱目魚）對砂蝦成長的影響，找尋最適合砂蝦的飼料；（3）鹽度對砂蝦存活率、耗氧、排氨、體水分和滲透壓生理反應的影響。 由水質和砂蝦成長的調查結果得知，因天氣變化的影響，鹽度急速下降和水中氨濃度急速升高，加上有機物的累積、長期溶氧不足和pH值變化大，造成砂蝦緊迫而大量死亡，收成也因此相對地不穩定，但只要有良好之管理仍有不錯之收成。 在比較飼料適用試驗方面，可以得知海水蝦的商業飼料明顯較虱目魚飼料能滿足砂蝦所需的營養。可能是受到飼料成份的影響，斑節蝦飼料蛋白質含量最高，但成長效果卻比白蝦飼料差。另外亦發現餵食商業飼料砂蝦之成長速率遠比室外粗放式養殖低，除了是現行海水蝦商業飼料仍無法滿足砂蝦所需的營養外，在室外因仍有甚多之天然食物亦為主要之因素。 在探討鹽度對砂蝦生理的影響方面，當降鹽速率大於每日10ppt，並超過48小時以後，才會造成約50％的死亡率，這可能是砂蝦能夠生活在鹽度急遽變化的半淡鹹水河口或海邊原因。養殖在1∼30ppt以內之各鹽度下，存活率無明顯的差異，顯示砂蝦能適應到極低鹽度。耗氧率有隨著鹽度升高而增加的趨勢，顯示池中在鹽度提高時，需增加水中的溶氧量，以降低砂蝦受到緊迫的機率。在3∼33ppt之間的砂蝦排氨率無差異。另外，隨著生活鹽度的降低，會造成體水分升高和滲透壓降低，顯示為了適應在不同鹽度下，滲透壓的調節對砂蝦是必行的工作，因此飼養砂蝦幼蝦時可馴化至稍低鹽度（15∼20ppt），獲得較佳的成長效率。

The sand shrimp（M. ensis）is one of the most important and commercial shrimp cultured with milkfish（C. chanos）in south-west coastal zone of Taiwan. When the aquacultural environment is deteriorated and full of the pathogenic bacteria, the culture harvest is not stable. In order to promote and maintain the sand shrimp’s unit area production, we must understand the aquatic environment and the nutrient requirement of sand shrimp. Therefore, the purpose of this studies aimed at as（1）To investigate the water quality in milkfish-shrimp polyculture pond and the growth rate of sand shrimp in Tainan Prefecture.（2）To compare the growth promoting effect of four commercial feedstuffs on sand shrimp.（3）To elucidate the effect of salinity on the survival rate, oxygen consumption, ammonia excretion and osmoregulation of juvenile sand shrimp. Our results demonstrated that the harvest of sand shrimp in three different ponds was not consistant due to the bad weather and fluctuation of pond salinity, ammonia, organic accumulation, dissolved oxygen and great pH values. High mortality juvenile and subadult sand shrimp was also noticed under the the stresses of lower dissolved oxygen and great pH variation. However, experimental ponds can have a profitable harvest, if better pond managements were paid. For growth rate comparison, it is found that feedstuffs for seawater shrimp are better than that for milkfish to feed sand shrimp. Among four different feedstuffs, the ingredients of whiteshrimp feed were more suitable for sand shrimp. With its growth performance being the best. However, the growth rate of sand shrimp fed with four different feedsuffs is lower than those reared in polyculture system, indicating the composition of commercial shrimp feed maybe not sufficient for the requirement of sand shrimp. Lack of natural food could be another reason. Salinity can affect the physiology of sand shrimp. Since the shrimp are osmo-comformer, it can tolerant of salinitydrop up to 7ppt/day. Even in low salinity（1∼10ppt）, the mortality was always kept the same as these in high sality. In addition, the oxygen consumption rate is positively correlated with the increasing salinity. Furthermore, the ammonia excretion rate was also slightly correlated with the external salinity(3∼33ppt) therefore, more paddlewheels in the higher salinity pond is recommanded. In low-salinity adapted group, hempolymph osmolarity of shrimp is decreased, while the whole body water content is increased. It is concluded that for growth promotion and survival increase, culture of sand shrimp shall be kept in low salinity（15-25ppt）.