Assessing the impacts of several algae-based diets on cultured European abalone (Haliotis tuberculata)

The effects of different algal diets on the mortality, apparent ingestion, weight, length and conversion rates of the European abalone (Haliotis tuberculata) maintained in a semi-closed seawater system throughout the year were compared. Various combinations of red algae (Palmaria palmata, Ceramium rubrum and Chondrus crispus cultured or harvested from the natural environment, as well as Porphyra spp. collected), brown algae (Laminaria digitata) and green algae (fresh or frozen Ulva intestinalis) were tested. The results showed that P. palmata, C. rubrum and U. intestinalis administered alone were associated with significantly higher weight growth rates than the other species of algae tested. However, some combinations of algae (i.e. different proportions of L. digitata in association with P. palmata) were more favorable for weight increase when compared with the expected rates calculated for the diet based on L. digitata alone. Limiting the amount of any of these foods substantially reduced the conversion rate. Seasonal trends were apparent in both weight increase and food conversion rates, with the result that growth in weight on a diet of L. digitata was fastest in summer. Growth on P. palmata was faster in each season, and reached a maximum in early spring. The data collected allowed us to model weight increase and month-to-month food conversion rates for a diet based on P. palmata and L. digitata. The data obtained in this study were coupled with data regarding the availability of algae during the year, enabling us to suggest an optimal diet for each of the four seasons. Finally, the effects of different algae diets were investigated on hemocyte parameters, and the result suggested that P. palmata would reinforce the immune system of abalone