Toxicity and antibacterial activity of silver ions in the rearing water of Japanese eel eggs and larvae

Abstract

To apply the antibacterial activity of silver ions to the rearing of Japanese eel Anguilla japonica larvae, we tested the effects of exposure to silver ions on hatching, survival and growth in eel larvae. Hatching rate of eggs was significantly decreased at a silver nitrate concentration of higher than 0,1 mg/L in rearing water (p<0,01), whereas the survival rates of 0 or 5-day-old larvae were not influenced by exposure to the same condition for 120 hours. However, the survival rates of those larvae were decreased by exposure to 1 mg/L silver nitrate for more than 24 hours. During long-term rearing experiments, the number of bacteria on the wall of the rearing tank was significantly reduced by intermittently (four times a day) adding silver nitrate (max. 1 mg/L) to rearing water, and larval survival rate at the early stage (5 to 60-day-old) became significantly higher than that in the normal rearing method (p< 0.05). Growth was not influenced by adding silver nitrate, and six larvae in the silver-added tank finally metamorphosed into glass eels without any morphological anomalies. These results suggest that the use of silver ions in rearing eel larvae can facilitate the efficient production of artificial glass eels.