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 afteralmost two decades of research. The production ofseabream (Sparus aurata), which reached over 750tons in 1995, is expected to reach an annualproduction ranging between 4000 - 12 700 metric tonsby year 2010. The anticipated introduction of newspecies and its expansion to the Mediterranean shoreline will help in leading the increased maricultureproduction. Two marine fish hatcheries that operatetoday in Israel produce 7 million fingerlings a year.Traditionally, aquaculture in Israel raises fish ininland freshwater ponds and irrigation reservoirs. Inaddition, Lake Kinneret, the only freshwater lake inIsrael, is stocked yearly with juvenile fish raised inlocal hatcheries (tilapia) or imported fromMediterranean countries (mugil). While culture offreshwater teleost species (carp) was introduced morethan fifty years ago, mariculture started on acommercial scale less than 5 years ago. The limitedsupply of freshwater will accelerate the futureculture of marine species.The bottleneck of almost all marine finfish productionlies in obtaining adequate numbers of fingerlings, dueto their high mortality at early life stages. Theproduction is hindered by inadequate supply of food toearly larval stages which require live food.Development of technologies in Israel for masscultivation of food chain organisms including algae,rotifers and brine shrimp followed their developmentin other parts of the world, most notably thoseachieved in Japan. The local commercial scaleproduction of rotifers relies on several batch orsemi-continuous cultures in conical or flatbottomrectangular containers that supply daily 0.6-4billion rotifers in each hatchery. Originally arelatively large local Brachionus plicatilisstrain was used, but later smaller B.rotundiformis strains were introduced, resulting ina mixture of undefined strains. The incorporation ofalgae (Nannochloropsis sp.) generated in highyield raceways contributes to the reliability ofrotifer cultures. Algae are supplied directly from theraceways or centrifuged and stored as a frozen pasteuntil required in the hatchery. The current dependablesupply of live cultures reduces the need for preservedstocks of rotifers, either as resting eggs or keptalive at low temperatures. To the fish grower,rotifers are live food capsules that deliver essentialnutrients (e.g. long chain unsaturated fatty acids)for growth and survival of fish larvae. Research aimedat replacing live food with chemically definedmicrodiets could reveal physiological principles inprey recognition and digestion of food by marine fishlarvae.