Mariculture in Israel — past achievements and future directions in raising rotifers as food for marine fish larvae

Abstract

Marine fish production is now being carried out after almost two decades of research. The production of seabream (Sparus aurata), which reached over 750 tons in 1995, is expected to reach an annual production ranging between 4,000 – 12,700 metric tons by year 2010. The anticipated introduction of new species and its expansion to the Mediterranean shore 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, Lake Kinneret, the only freshwater lake in Israel, is stocked yearly with juvenile fish raised in local hatcheries (tilapia) or imported from Mediterranean countries (mugil). While culture of freshwater teleost species (carp) was introduced more than fifty years ago, mariculture started on a commercial scale less than 5 years ago. The limited supply of 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 to early larval stages which require live food. Development of technologies in Israel for mass cultivation of food chain organisms including algae, rotifers and brine shrimp followed their development in other parts of the world, most notably those achieved in Japan. The local commercial scale production of rotifers relies on several batch or semi-continuous cultures in conical or flatbottom rectangular containers that supply daily 0.6–4 billion rotifers in each hatchery. Originally a relatively large local Brachionus plicatilis strain was used, but later smaller B. rotundiformis strains were introduced, resulting in a mixture of undefined strains. The incorporation of algae (Nannochloropsis sp.) generated in high yield raceways contributes to the reliability of rotifer cultures. Algae are supplied directly from the raceways or centrifuged 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 acids) for growth and survival of fish larvae. Research aimed at replacing live food with chemically defined microdiets could reveal physiological principles in prey recognition and digestion of food by marine fish larvae.