engleski

The use of the diatom Cylindrotheca closterium in the feeding of Ostrea edulis larvae

The cultivation of European flat oyster Ostrea edulis in Croatia is fully dependent on the collection of larvae from the natural environment. In recent years, the initial phase of production suffered a dramatic decrease in the number of larvae available from nature. Artificial spawning in hatcheries is the only alternative for the sustainability of the industry. Cultured unicellular algae have been used provide nutrition to all stages of bivalve species. Cylindrotheca closterium is an abundant diatom species in the natural environment during the spawning season of the flat oyster in the Adriatic area where the broodstock used in the experiment originated. The aim of this study was to test C. closterium as a feed source during larval development in the hatchery. This species showed good performance as a feed ingredient for the broodstock of oysters, clams and abalone. The development of embryos of the flat oyster, Ostrea edulis, from the early shell valve formation to the eyed pediveliger stage, was examined under two different diets by measuring larval growth and survival. Larvae were raised at the stocking density of 5 individuals per milliliter in a closed recirculation system under optimal water quality conditions and a constant temperature of 21±1ºC. For the initial four days of feeding, the diet was the same for two experimental groups, and consisted of the mixture of two flagellates, Isochrisys galbana and Tetraselmis suecica. The experiment was conducted in duplicate. After day four, 40% of the flagellates were replaced by diatoms: Chaetoceros muelleri for one group of larvae, and C. closterium for the second group. The density of microalgae in the culture tanks was maintained at 100 cells/µl of I. galbana equivalents. Larval growth and survival were observed from day four when the two different feeding regimes were applied. The diameter of larvae was measured every second day as well as the number of larvae per ml. From day 10 till the end of the experiment, the group fed with C. muelleri grew progressively better, but with no statistically significant difference, as is depicted in the Fig. 1. Significantly better survival of 41% for the group fed with C. muelleri, in comparison with 14% for the second group, was recorded at the end of the experiment. Results showed that C. closterium was not a good replacement for the commonly used diatom C.muelleri in the cultivation of oyster larvae, in spite of its successful use in broodstock conditioning of different shellfish species.

Cylindrotheca closterium; oyster larvae; Ostrea edulis; feeding

nije evidentirano