CONTROL OF WATER-QUALITY IN THE CULTURE OF EARLY-STAGE PHYLLOSOMAS OFPANULIRUS-JAPONICUS

A method for culturing phyllosomas of spiny lobster is characterized b y use of the microalga Nannochloropsis oculata in the phyllosoma cultu re water. The method seems to be most effective during the microalgae growth phase due to the water purification activity of the microalgae. Ln contrast, accumulation of microalgae during the declining phase ma y cause a deterioration of water quality. The period necessary between changes of the culture medium was determined for early stage phylloso mas of Panulirus japonicus. The culture water was initially light gree n. The color gradually deepened and changed to yellow. The amount of c hlorophyll a was relatively stable. Carotenoids/Chlorophyll a ratio wa s initially 0.30 and increased to 0.50 over about 2 wks. Chemical oxyg en demand (COD) steadily increased to 1.2 - 1.5 ppm after 14 - 19 d. T he rate of COD increase was lower in cultures which had higher microal gae growth rates. The initial concentration of ammonia-N, about 0.4 pp m, at the addition of the microalgae, which was removed within a few d ays. The bacterial number ranged between 4 x 10(3) and 3 x 10(4), and no significant effect due to bacteria was observed. Survival rate of p hyllosomas was best when the culture water was changed every 13-14 d a t initial concentration of Nannochloropsis at one million cells ml(-1) and allowed to remain unchanged for 34 d.