Notojima Station, National Center for Stock Enhancement, Fisheries Research Agency, Notojima, Ishikawa 926-0216, Japan
This study investigated the suitable temperature for mass culture of the rotifer, Brachionus plicatilis, in order to optimize the rearing of Japanese flounder, Paralichthys olivaceus, in terms of larval growth and vitality. Two-day batch cultures of rotifers were prepared daily at three graduated temperatures (18°C, 23°C, 28°C). Rotifers were harvested on day 2 from the start of cultivation, and then enriched at 18°C, the same temperature as larval rearing. Rotifers were supplied to the flounder larvae until 19 days post hatching (dph) at each temperature. Rotifers cultured at 23°C and 28°C had higher ratios of immature individuals, and their physiological state (e.g. egg ratio) after enrichment was poor. During 15-20 dph, larvae fed rotifers cultured at 18°C showed higher performance in growth and morphological development than those fed rotifers cultured at 23°C and at 28°C. All groups of larvae at 20 dph were evaluated according to starvation tolerance tests, when the larvae that had been fed 28°C rotifers had the lowest survival (P<0.05). The thermal difference between rotifer mass culture and larval rearing had a large influence on the rearing efficiency of Japanese flounder larvae.