Long-term rearing of Japanese eel larvae using a liquid-type diet: food intake, survival and growth

The efficiency of a new liquid-type diet for long-term rearing of Japanese eel larvae until metamorphosis was examined, as was the effect of diet viscosity on diet intake and on the survival and growth of early larvae. The highest intake of the experimental diet by 6- and 9-day post-hatch (dph) larvae occurred at viscosities of 20–50 mPa·s, much lower than the viscosity of the currently used slurry-type diet (ca. 2900 mPa·s). Long-term feeding trials for 259 days ( n = 4) showed that overall survival rates of larvae (37–59%) fed a liquid-type diet with lower viscosity (40–680 mPa·s) were 2 to 3.4 times higher than the survival rates of larvae fed the slurry-type diet (11–25%). Because nutrients were diluted in the liquid-type diet, the growth of larvae fed this diet was slower after about 200 days and metamorphosis was delayed. However, the yield of glass eels was 1.1 to 3.2 times higher in larvae fed the liquid than the slurry diet. These findings suggest that feeding the liquid-type diet can result in the mass production of glass eels by ensuring high growth, survival and metamorphosis rates.