Effects of Seawater Elements on Growth, Survival Rate, and Whole-body Mineral Concentration of the Ocellate Puffer Takifugu rubripes Larvae and Juveniles

摘要

Fish, unlike mammals and birds, can absorb elements from food as well as the surrounding water. To determine the requirements of the ocellate puffer Takifugu rubripes with regard to elements derived from seawater, we reared the larvae and juveniles ofthis fish in seawater with various compositions. This included filtered natural seawater, complete artificial seawater, and complete artificial seawater in which certain elements (sodium, magnesium, potassium, calcium, boron, bromine, sulfur, strontium,and fluorine) were selectively omitted. Larvae were reared for 40 days in all treatment groups, after which survival rate, total length, and whole-body element concentration were measured. Larvae died after a few days in the seawater lacking sodium, calcium, and potassium; there were no significant differences in survival among other treatments. Total lengths in the element-deficient groups were similar to those in the natural seawater and complete artificial seawater groups at the end of experiment. However, the whole-body magnesium and strontium contents were significantly reduced in each of the corresponding element-deficient groups. Further, the whole-body sodium, calcium, and strontium concentration in the magnesium-deficient group was remarkablychanged. Hence, we concluded that sodium, potassium, and calcium are essential elements in seawater for ocellate puffer survival. Moreover, fish require magnesium and may need other elements in seawater depend on the dietary elements level.