Use of Strontium Chloride in Otolith Marking of Japanese Flounder

Abstract:

In the management of stock enhanced Japanese flounder, it is often necessary to distinguish those that are hatchery-reared, from wild stocks. This study examines the feasibility of marking Japanese flounder by feeding them a diet enriched with strontium. To achieve nominally different concentrations of strontium in the fish food, 1, 8, and 64 g of strontium chloride crystals (SrCl2∙6H2O) were each dissolved in 1 L of distilled water and sprayed onto 1 kg of pelleted feed. The treatments groups of fish were fed the pellets for 10 d, then farmed for 30 days, and then sampled. Our data shows that both the 8 g SrCl2/kg feed and 64 g SrCl2/kg feed resulted in a mark on the otoliths of the Japanese flounder. The peak concentration of strontium (8 g SrCl2/kg), often resulted in otoliths with concentrations two orders of magnitude higher than those found in the control fish. The concentration of strontium in the 64 g SrCl2/ kg feed, resulted in a 6-fold or 18-fold increases in the otoliths. The strontium value increased with the increased concentration of strontium in the pellet feed. The results also showed that strontium was safe for the fish and did not negatively affect their mortality. The total body length of the treatment groups with 1 and 8 g SrCl2/kg, were (11.11±1.32) cm and (10.88±1.07) cm, respectively, in which the length growth rate was faster than that of the control group and the treatment group with 64 g SrCl2/kg feed (P≤0.05). With appropriate strontium concentrations, the growth of the Japanese flounder youth was enhanced. Our results suggest that feeding a diet enriched in strontium could be an effective means of marking hatchery-reared Japanese flounder for stock enhancement.