MARICULTURE IN ISRAEL - PAST ACHIEVEMENTS AND FUTURE-DIRECTIONS IN RAISING ROTIFERS AS FOOD FOR MARINE FISH LARVAE

Marine fish production is now being carried out after almost two decad es of research. The production of seabream (Sparus aurata), which reac hed over 750 tons in 1995, is expected to reach an annual production r anging between 4,000-12,700 metric tons by year 2010. The anticipated introduction of new species and its expansion to the Mediterranean sho re line will help in leading the increased mariculture production. Two marine fish hatcheries that operate today in Israel produce 7 million fingerlings a year. Traditionally, aquaculture in Israel raises fish in inland freshwater ponds and irrigation reservoirs. In addition, Lak e Kinneret, the only freshwater lake in Israel, is stocked yearly with juvenile fish raised in local hatcheries (tilapia) or imported from M editerranean countries (mugil). While culture of freshwater teleost sp ecies (carp) was introduced more than fifty years ago, mariculture sta rted on a commercial scale less than 5 years ago. The limited supply o f freshwater will accelerate the future culture of marine species. The bottleneck of almost all marine finfish production lies in obtaining adequate numbers of fingerlings, due to their high mortality at early life stages. The production is hindered by inadequate supply of food t o early larval stages which require live food. Development of technolo gies in Israel for mass cultivation of food chain organisms including algae, rotifers and brine shrimp followed their development in other p arts of the world, most notably those achieved in Japan. The local com mercial scale production of rotifers relies on several batch or semi-c ontinuous cultures in conical or flatbottom rectangular containers tha t supply daily 0.6-4 billion rotifers in each hatchery. Originally a r elatively large local Brachionus plicatilis strain was used, but later smaller B. rotundiformis strains were introduced, resulting in a mixt ure of undefined strains. The incorporation of algae (Nannochloropsis sp.) generated in high yield raceways contributes to the reliability o f rotifer cultures. Algae are supplied directly from the raceways or c entrifuged and stored as a frozen paste until required in the hatchery . The current dependable supply of live cultures reduces the need for preserved stocks of rotifers, either as resting eggs or kept alive at low temperatures. To the fish grower, rotifers are live food capsules that deliver essential nutrients (e.g. long chain unsaturated fatty ac ids) for growth and survival of fish larvae. Research aimed at replaci ng live food with chemically defined microdiets could reveal physiolog ical principles in prey recognition and digestion of food by marine fi sh larvae.