Trends in nursery rearing of bivalve molluscs

Nursery rearing of bivalve molluscs, as the intermediate step between the controlled production of larvae in commercial hatcheries and the growout in the wild, is a practice which is receiving more and more attention in mollusc farming. The purpose of nursery rearing of bivalves is to culture cultchless spat of a few millimeters in size, up to 1-2 cm, in a minimum of time, in densities as high as possible, and at minimal costs and risks. In the last decade various technologies for nursery culturing, indoors as well as outdoors, have been developed at different places, ranging from suspended culture in the open sea to controlled onshore culture in upwelling cylinders. This paper reviews the different systems developed until now, with special emphasis on one of the key problems, namely the supply of the right amount of suitable food for the juvenile bivalves, in function of flow rates, stocking densities, and temperature. The growth and mortality rates of Ostrea edulis, Crassostrea gigas, Venerupis semidecussata, Mercenaria mercenaria, Argopecten irradians and Crassostrea virginica, under nursery conditions is discussed. A few considerations are made with regard to the economic aspects of nursery operations